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Cycling

Cycling, also known as bicycling or biking, is the activity of riding a bicycle or other type of cycle. It encompasses the use of human-powered vehicles such as balance bikes, unicycles, tricycles, and quadricycles. Cycling is practised around the world for purposes including transport, recreation, exercise, and competitive sport.

History
Cycling became popularized in Europe and North America in the latter part and especially the last decade of the 19th century. Today, over 50 percent of the human population knows how to ride a bike.

War
The bicycle has been used as a method of reconnaissance as well as transporting soldiers and supplies to combat zones. In this it has taken over many of the functions of horses in warfare. In the Second Boer War, both sides used bicycles for scouting. In World War I, France, Germany, Australia and New Zealand used bicycles to move troops. In its 1937 invasion of China, Japan employed some 50,000 bicycle troops, and similar forces were instrumental in Japan's march or "roll" through Malaya in World War II. Germany used bicycles again in World War II, while the British employed airborne "Cycle-commandos" with folding bikes.

In the Vietnam War, communist forces used bicycles extensively as cargo carriers along the Ho Chi Minh Trail.

The last country known to maintain a regiment of bicycle troops was Switzerland, which disbanded its last unit in 2003.

Equipment

In many countries, the most commonly used vehicle for road transport is a utility bicycle. These have frames with relaxed geometry, protecting the rider from shocks of the road and easing steering at low speeds. Utility bicycles tend to be equipped with accessories such as mudguards, pannier racks and lights, which extends their usefulness on a daily basis. Since the bicycle is so effective as a means of transportation, various companies have developed methods of carrying anything from the weekly shop to children on bicycles. Certain countries rely heavily on bicycles and their culture has developed around the bicycle as a primary form of transport. In Europe, Denmark and the Netherlands have the most bicycles per capita and most often use bicycles for everyday transport.

Road bikes tend to have a more upright shape and a shorter wheelbase, which make the bike more mobile but harder to ride slowly. The design, coupled with low or dropped handlebars, requires the rider to bend forward more, making use of stronger muscles (particularly the gluteus maximus) and reducing air resistance at high speed.

Road bikes are designed for speed and efficiency on paved roads. They are characterized by their lightweight frames, skinny tires, drop handlebars, and narrow saddles. Road bikes are ideal for racing, long-distance riding, and fitness training.

Other common types of bikes include gravel bikes, designed for use on gravel roads or trails, but with the ability to ride well on pavement, mountain bikes which are designed for more rugged, undulating terrain, and e-bikes which provide some level of motorized assist for the rider. There are additional variations of bikes and types of biking as well.

The price of a new bicycle can range from US$50 to more than US$20,000 (the highest priced bike in the world is the custom Madone by Damien Hirst, sold at US$500,000 ), depending on quality, type and weight (the most exotic road bicycles can weigh as little as 3.2 kg (7 lb) ). However, UCI regulations stipulate a legal race bike cannot weigh less than 6.8 kg (14.99 lbs). Being measured for a bike and taking it for a test ride are recommended before buying.

The drivetrain components of the bike should also be considered. A middle grade dérailleur is sufficient for a beginner, although many utility bikes are equipped with hub gears. If the rider plans a significant amount of hillclimbing, a triple-chainrings crankset gear system may be preferred. Otherwise, the relatively lighter, simpler, and less expensive double chainring is preferred, even on high-end race bikes. Much simpler fixed wheel bikes are also available.

Many road bikes, along with mountain bikes, include clipless pedals to which special shoes attach, via a cleat, enabling the rider to pull on the pedals as well as push. Other possible accessories for the bicycle include front and rear lights, bells or horns, child carrying seats, cycling computers with GPS, locks, bar tape, fenders (mud-guards), baggage racks, baggage carriers and pannier bags, water bottles and bottle cages.

For basic maintenance and repairs cyclists can carry a pump (or a CO2 cartridge), a puncture repair kit, a spare inner tube, and tire levers and a set of allen keys. Cycling can be more efficient and comfortable with special shoes, gloves, and shorts. In wet weather, riding can be more tolerable with waterproof clothes, such as cape, jacket, trousers (pants) and overshoes and high-visibility clothing is advisable to reduce the risk from motor vehicle users.

Items legally required in some jurisdictions, or voluntarily adopted for safety reasons, include bicycle helmets, generator or battery operated lights, reflectors, and audible signalling devices such as a bell or horn. Extras include studded tires and a bicycle computer.

Bikes can also be heavily customized, with different seat designs and handle bars, for example. Bicycle Gears can also be customized to better suit the rider's strength in relation to the terrain.

Skills
Many schools and police departments run educational programs to instruct children in bicycle handling skills, especially to introduce them to the rules of the road as they apply to cyclists. In some countries these may be known as bicycle rodeos, or operated as schemes such as Bikeability in the UK. Education for adult cyclists is available from organizations such as the League of American Bicyclists.

Beyond simply riding, another skill is riding efficiently and safely in traffic. One popular approach to riding in motor vehicle traffic is vehicular cycling, occupying road space as car does. Alternately, in countries such as Denmark and the Netherlands, where cycling is popular, cyclists are often segregated into bike lanes at the side of, or more often separate from, main highways and roads. Many primary schools participate in the national road test in which children individually complete a circuit on roads near the school while being observed by testers.

Infrastructure

Cyclists, pedestrians and motorists make different demands on road design which may lead to conflicts. Some jurisdictions give priority to motorized traffic, for example setting up one-way street systems, free-right turns, high capacity roundabouts, and slip roads. Others share priority with cyclists so as to encourage more cycling by applying varying combinations of traffic calming measures to limit the impact of motorized transport, and by building bike lanes, bike paths and cycle tracks. The provision of cycling infrastructure varies widely between cities and countries, particularly since cycling for transportation almost entirely occurs in public streets. And, the development of computer vision and street view imagery has provided significant potential to assess infrastructure for cyclists.

In jurisdictions where motor vehicles were given priority, cycling has tended to decline while in jurisdictions where cycling infrastructure was built, cycling rates have remained steady or increased. Occasionally, extreme measures against cycling may occur. In Shanghai, where bicycles were once the dominant mode of transport, bicycle travel on a few city roads was banned temporarily in December 2003.

In areas in which cycling is popular and encouraged, cycle-parking facilities using bicycle stands, lockable mini-garages, and patrolled cycle parks are used to reduce theft. Local governments promote cycling by permitting bicycles to be carried on public transport or by providing external attachment devices on public transport vehicles. Conversely, an absence of secure cycle-parking is a recurring complaint by cyclists from cities with low modal share of cycling.

Extensive cycling infrastructure may be found in some cities. Such dedicated paths in some cities often have to be shared with in-line skaters, scooters, skateboarders, and pedestrians. Dedicated cycling infrastructure is treated differently in the law of every jurisdiction, including the question of liability of users in a collision. There is also some debate about the safety of the various types of separated facilities.

Bicycles are considered a sustainable mode of transport, especially suited for urban use and relatively shorter distances when used for transport (compared to recreation). Case studies and good practices (from European cities and some worldwide examples) that promote and stimulate this kind of functional cycling in cities can be found at Eltis, Europe's portal for local transport.

A number of cities, including Paris, London and Barcelona, now have successful bike hire schemes designed to help people cycle in the city. Typically these feature utilitarian city bikes which lock into docking stations, released on payment for set time periods. Costs vary from city to city. In London, initial hire access costs £2 per day. The first 30 minutes of each trip is free, with £2 for each additional 30 minutes until the bicycle is returned.

In the Netherlands, many roads have one or two separate cycleways alongside them, or cycle lanes marked on the road. On roads where adjacent bike paths or cycle tracks exist, the use of these facilities is compulsory, and cycling on the main carriageway is not permitted. Some 35,000 km of cycle-track has been physically segregated from motor traffic, equal to a quarter of the country's entire 140,000 km road network. A quarter of all trips in the country are made on bicycles, one quarter of them to work. Even the prime minister goes to work by bicycle, when weather permits. This saves the lives of 6,000 citizens per year, prolongs life expectancy by 6 months, saves the country 20 million dollars per year, and prevents 150 grams of from being emitted per kilometer of cycling.

Utility

Utility cycling refers both to cycling as a mode of daily commuting transport as well as the use of a bicycle in a commercial activity, mainly to transport goods, mostly accomplished in an urban environment.

The postal services of many countries have long relied on bicycles. The British Royal Mail first started using bicycles in 1880; now bicycle delivery fleets include 37,000 in the UK, 25,700 in Germany, 10,500 in Hungary and 7000 in Sweden. In Australia, Australia Post has also reintroduced bicycle postal deliveries on some routes due to an inability to recruit sufficient licensed riders willing to use their uncomfortable motorbikes. The London Ambulance Service has recently introduced bicycling paramedics, who can often get to the scene of an incident in Central London more quickly than a motorized ambulance.

The use of bicycles by police has been increasing, since they provide greater accessibility to bicycle and pedestrian zones and allow access when roads are congested. In some cases, bicycle officers have been used as a supplement or a replacement for horseback officers.

Bicycles enjoy substantial use as general delivery vehicles in many countries. In the UK and North America, as their first jobs, generations of teenagers have worked at delivering newspapers by bicycle. London has many delivery companies that use bicycles with trailers. Most cities in the West, and many outside it, support a sizeable and visible industry of cycle couriers who deliver documents and small packages. In India, many of Mumbai's Dabbawalas use bicycles to deliver home cooked lunches to the city's workers. In Bogotá, Colombia the city's largest bakery recently replaced most of its delivery trucks with bicycles. Even the car industry uses bicycles. At the huge Mercedes-Benz factory in Sindelfingen, Germany workers use bicycles, color-coded by department, to move around the factory.

Bicycle touring

Bicycles are used for recreation at all ages. Bicycle touring, also known as cyclotourism, involves touring and exploration or sightseeing by bicycle for leisure. Bicycle tourism has been one of the most popular sports for recreational benefit. A brevet or randonnée is an organized long-distance ride.

One popular Dutch pleasure is the enjoyment of relaxed cycling in the countryside of the Netherlands. The land is very flat and full of public bicycle trails and cycle tracks where cyclists are not bothered by cars and other traffic, which makes it ideal for cycling recreation. Many Dutch people subscribe every year to an event called fietsvierdaagse — four days of organised cycling through the local environment. Paris–Brest–Paris (PBP), which began in 1891, is the oldest bicycling event still run on a regular basis on the open road, covers over 1200 km and imposes a 90-hour time limit. Similar if smaller institutions exist in many countries.

A study conducted in Taiwan improved the environmental quality for bicyclist tourists which demonstrated greater health benefits in tourists and even in natives. The number of bicyclists in Taiwan increased from 700,000 in 2008 to 5.1 million in 2017. Thus, this resulted in more and safer bicycle routes to be established. When cycling, cyclists take into account the safety on the road, bicycle lanes, smooth roads, diverse scenery, and ride length. Thus, the environment plays a huge role in people's decision factor to use bicycle touring more. This study used many questionnaires and conducted statistical analysis to come up with the conclusion of cyclists' top 5 factors that they consider before making a decision to bike are: safety, lighting facility, design of lanes, the surrounding landscape, and how clean the environment is. Thus, after improving these 5 factors, they found much more recreational benefits to bicycle tourism.

Organized rides
Many cycling clubs hold organized rides in which bicyclists of all levels participate. The typical organized ride starts with a large group of riders, called the mass, bunch or even peloton. This will thin out over the course of the ride. Many riders choose to ride together in groups of the same skill level to take advantage of drafting.

Most organized rides, for example cyclosportives (or gran fondos), Challenge Rides or reliability trials, and hill climbs include registration requirements and will provide information either through the mail or online concerning start times and other requirements. Rides usually consist of several different routes, sorted by mileage, and with a certain number of rest stops that usually include refreshments, first aid and maintenance tools. Routes can vary by as much as 100 mi.

Some organized rides are entirely social events. One example is the monthly San Jose Bike Party which can reach attendance of one to two thousand riders in Summer months.

Mountain
Mountain biking began in the 1970s, originally as a downhill sport, practised on customized cruiser bicycles around Mount Tamalpais. Most mountain biking takes place on dirt roads, trails and in purpose-built parks. Downhill mountain biking has just evolved in the recent years and is performed at places such as Whistler Mountain Bike Park. Slopestyle, a form of downhill, is when riders do tricks such as tailwhips, 360s, backflips and front flips. There are several disciplines of mountain biking besides downhill, including: cross country (often referred to as XC), all mountain, trail, free ride, and newly popular enduro.

In 2020, due to COVID-19, mountain bikes saw a surge in popularity in the US, with some vendors reporting that they were sold out of bikes under US$1000.

Other
The Marching and Cycling Band HHK from Haarlem (the Netherlands) is one of the few marching bands around the world which also performs on bicycles.

Racing

Shortly after the introduction of bicycles, competitions developed independently in many parts of the world. Early races involving boneshaker style bicycles were predictably fraught with injuries. Large races became popular during the 1890s "Golden Age of Cycling", with events across Europe, and in the U.S. and Japan as well. At one point, almost every major city in the US had a velodrome or two for track racing events, however since the middle of the 20th century cycling has become a minority sport in the US whilst in Continental Europe it continues to be a major sport, particularly in the United Kingdom, France, Belgium, Italy and Spain. The most famous of all bicycle races is the Tour de France. This began in 1903, and continues to capture the attention of the sporting world.

In 1899, Charles Minthorn Murphy became the first man to ride his bicycle a mile in under a minute (hence his nickname, Mile-a-Minute Murphy), which he did by drafting a locomotive at New York's Long Island.

As the bicycle evolved its various forms, different racing formats developed. Road races may involve both team and individual competition, and are contested in various ways. They range from the one-day road race, criterium, and time trial to multi-stage events like the Tour de France and its sister events which make up cycling's Grand Tours. Recumbent bicycles were banned from bike races in 1934 after Marcel Berthet set a new hour record in his Velodyne streamliner (49.992 km on 18 November 1933). Track bicycles are used for track cycling in Velodromes, while cyclo-cross races are held on outdoor terrain, including pavement, grass, and mud. Cyclocross races feature human-made features such as small barriers which riders either bunny hop over or dismount and walk over. Time trial races, another form of road racing require a rider to ride against the clock. Time trials can be performed as a team or as a single rider. Bikes are changed for time trial races, using aero bars. In the past decade, mountain bike racing has also reached international popularity and is even an Olympic sport.

Professional racing organizations place limitations on the bicycles that can be used in the races that they sanction. For example, the Union Cycliste Internationale, the governing body of international cycle sport (which sanctions races such as the Tour de France), decided in the late 1990s to create additional rules which prohibit racing bicycles weighing less than 6.8 kilograms (14.96 pounds). The UCI rules also effectively ban some bicycle frame innovations (such as the recumbent bicycle) by requiring a double triangle structure.

Activism
Many broad and correlated themes run in bicycle activism: one is about advocating the bicycle as an alternative mode of transport, and another is about the creation of conditions to permit and/or encourage bicycle use, both for utility and recreational cycling. Although the first emphasizes the potential for energy and resource conservation and health benefits gained from cycling versus automobile use, is relatively undisputed, the second is the subject of much debate.

It is generally agreed that improved local and inter-city rail services and other methods of mass transportation (including greater provision for cycle carriage on such services) create conditions to encourage bicycle use. However, there are different opinions on the role of various types of cycling infrastructure in building bicycle-friendly cities and roads.

Some bicycle activists (including some traffic management advisers) seek the construction of bike paths, cycle tracks and bike lanes for journeys of all lengths and point to their success in promoting safety and encouraging more people to cycle. Some activists, especially those from the vehicular cycling tradition, view the safety, practicality, and intent of such facilities with suspicion. They favor a more holistic approach based on the 4 'E's: education (of everyone involved), encouragement (to apply the education), enforcement (to protect the rights of others), and engineering (to facilitate travel while respecting every person's equal right to do so). Some groups offer training courses to help cyclists integrate themselves with other traffic.

Critical Mass is an event typically held on the last Friday of every month in cities around the world where bicyclists take to the streets en masse. While the ride was founded with the idea of drawing attention to how unfriendly the city was to bicyclists, the leaderless structure of Critical Mass makes it impossible to assign it any one specific goal. In fact, the purpose of Critical Mass is not formalized beyond the direct action of meeting at a set location and time and traveling as a group through city streets.

There is a long-running cycle helmet debate among activists. The most heated controversy surrounds the topic of compulsory helmet use.

It is paradoxical that in many developing countries cycling is in decline as bicycles are replaced by motorbikes and cars, while in many developed countries cycling is on the rise.

Equality
Within western societies the demographic of those who cycle is often not representative of broader society. Research by TfL in London, UK, suggests that cyclists in London are typically 'white, under 40, male, with medium to high household income.' Studies from large-scale representative data from Germany show that people with higher levels of education cycle substantially more often than those with lower levels of education. Even for trips of the same distance and among people from the same city with the same income level, those with higher education cycle more. As a result, there are various forms of activism focused on diversifying the cycling community. Inspired by the Black Lives Matter movement are organizations such as Street Riders NYC that seek to protest while on bicycles about systemic racism and police brutality. An incidental experience for Street Riders NYC protest participants is the inequity in where safe bicycling infrastructure exists by neighbourhood, which is interpreted as a form of classism within cycling and urbanism. The bicycle has acted as a means for women's liberation and thus has links to feminism.

Associations
Cyclists form associations, both for specific interests (trails development, road maintenance, bike maintenance, urban design, racing clubs, touring clubs, etc.) and for more global goals (energy conservation, pollution reduction, promotion of fitness). Some bicycle clubs and national associations became prominent advocates for improvements to roads and highways. In the United States, the League of American Wheelmen lobbied for the improvement of roads in the last part of the 19th century, founding and leading the national Good Roads Movement. Their model for political organization, as well as the paved roads for which they argued, facilitated the growth of the automobile.

In Europe, the European Cyclists' Federation represents around 70 local, regional and national civil society organisations across more than 40 countries that work to promote cycling as a mode of transport and leisure.

As a sport, cycling is governed internationally by the Union Cycliste Internationale in Switzerland, USA Cycling (merged with the United States Cycling Federation in 1995) in the United States, (for upright bicycles) and by the International Human Powered Vehicle Association (for other HPVs, or human-powered vehicles). Cycling for transport and touring is promoted on a European level by the European Cyclists' Federation, with associated members from Great Britain, Japan and elsewhere. Regular conferences on cycling as transport are held under the auspices of Velo City; global conferences are coordinated by Velo Mondial.

Cycling as a means of transportation
Cycling is widely regarded as an effective and efficient mode of transportation optimal for short to moderate distances.

Bicycles provide numerous possible benefits in comparison with motor vehicles, including the sustained physical exercise involved in cycling, easier parking, increased maneuverability, and access to roads, bike paths and rural trails. Cycling also offers a reduced consumption of fossil fuels, less air and noise pollution, reduced greenhouse gas emissions, and greatly reduced traffic congestion. These have a lower financial cost for users as well as for society at large (negligible damage to roads, less road area required). By fitting bicycle racks on the front of buses, transit agencies can significantly increase the areas they can serve.

Among the disadvantages of cycling are the requirement of bicycles (excepting tricycles or quadricycles) for the rider to have certain level of basic skill to remain upright, the reduced protection in crashes in comparison to motor vehicles, often longer travel time (except in densely populated areas), vulnerability to weather conditions, difficulty in transporting passengers, and the fact that a basic level of fitness is required for cycling moderate to long distances.

Health effects
Cycling provides a variety of health benefits and reduces the risk of cancers, heart disease, and diabetes that are prevalent in sedentary lifestyles. Cycling on stationary bikes have also been used as part of rehabilitation for lower limb injuries, particularly after hip surgery. Individuals who cycle regularly have also reported mental health improvements, including less perceived stress and better vitality.

The health benefits of cycling outweigh the risks, when cycling is compared to a sedentary lifestyle. A Dutch study found that cycling can extend lifespans by up to 14 months, but the risks equated to a reduced lifespan of 40 days or less. Mortality rate reduction was found to be directly correlated to the average time spent cycling, totaling to approximately 6500 deaths prevented by cycling. Cycling in the Netherlands is often safer than in other parts of the world, so the risk-benefit ratio will be different in other regions. Overall, benefits of cycling or walking have been shown to exceed risks by ratios of 9:1 to 96:1 when compared with no exercise at all, including a wide variety of physical and mental outcomes.

Exercise
The physical exercise gained from cycling is generally linked with increased health and well-being. According to the World Health Organization (WHO), physical inactivity is second only to tobacco smoking as a health risk in developed countries, and is associated with 20-30% increased risk of various cancers, heart disease, and diabetes and tens of billions of dollars of healthcare costs. The WHO's 2009 report suggests that increasing physical activity is a public health "best buy", and that cycling is a "highly suitable activity" for this purpose. The charity Sustrans reports that investment in cycling provision can give a 20:1 return from health and other benefits. It has been estimated that, on average, approximately 20 life-years are gained from the health benefits of road bicycling for every life-year lost through injury.

Bicycles are often used by people seeking to improve their fitness and cardiovascular health. Recent studies on the use of cycling for commutes have shown that it reduces the risk of cardiovascular outcomes by 11%, with slightly more risk reduction in women than in men. In addition, cycling is especially helpful for those with arthritis of the lower limbs who are unable to pursue sports that cause impact to the knees and other joints. Since cycling can be used for the practical purpose of transportation, there can be less need for self-discipline to exercise.

Cycling while seated is a relatively non-weight bearing exercise that, like swimming, does little to promote bone density. Cycling up and out of the saddle, on the other hand, does a better job by transferring more of the rider's body weight to the legs. However, excessive cycling while standing can cause knee damage It used to be thought that cycling while standing was less energy efficient, but recent research has proven this not to be true. Other than air resistance, there is no wasted energy from cycling while standing, if it is done correctly.

Cycling on a stationary cycle is frequently advocated as a suitable exercise for rehabilitation, particularly for lower limb injury, owing to the low impact which it has on the joints. In particular, cycling is commonly used within knee rehabilitation programs, to strengthen the quadriceps muscles with minimal stress on the knee ligaments. Further stress of the knee can be relieved by changing seat heights and pedal position to improve the rehabilitation. Cycling is also used for rehabilitation after hip surgery to manage soft-tissue healing, control swelling and pain, and allow a larger range of motion to the nearby muscles earlier during recovery. As a result, many institutions have established a rehabilitation protocol that involves stationary cycling as part of the recovery process. One such protocol offered by Mayo Clinic recommends 2–4 weeks of cycling on an upright stationary bike following hip arthroscopy, starting from 5 minutes per session and slowly increasing to 30 minutes per session. The goal of these sessions are to reduce joint inflammation and maintain the widest range of motion possible with limited pain.

As a response to the increased global sedentary lifestyles and consequent overweight and obesity, one response that has been adopted by many organizations concerned with health and environment is the promotion of Active travel, which seeks to promote walking and cycling as safe and attractive alternatives to motorized transport. Given that many journeys are for relatively short distances, there is considerable scope to replace car use with walking or cycling, though in many settings this may require some infrastructure modification, particularly to attract the less experienced and confident.

An Italian study assessed the impact of cycling for commute on major non-communicable diseases and public healthcare costs. Using a health economic assessment model, the study found a lower incidence of type 2 diabetes, acute myocardial infarction, and stroke in individuals that cycled compared to those that did not actively commute. This model estimated that public healthcare costs would reduce by 5% over a 10-year period.

Illinois designated cycling as its official state exercise in 2007.

Mental health
The effects of cycling on overall mental health have often been studied. A European study surveying participants from seven cities about self-perceived health based on primary modes of transportation reported favorable results in the bicycle use population. The bicycle use group reported predominantly good self-perceived health, less perceived stress, better mental health, better vitality, and less loneliness. The study attributed these results to possible economic benefits and senses of both independence and identity as a member of a cyclist community. An English study recruiting non-cyclist older adults aged 50 to 83 to participate as either conventional pedal bike cyclists, electrically assisted e-bike cyclists, or a non-cyclist control group in outdoor trails measured cognitive function through executive function, spatial reasoning, and memory tests and well-being through questionnaires. The study did not find significant differences in spatial reasoning or memory tests. It did, however, find that both cyclists groups had improved executive function and well-being, both with greater improvement in the e-bike group. This suggested that non-physical factors of cycling such as independence, engagement with the outdoor environment, and mobility play a greater role in improving mental health.

A 15-month randomized controlled trial in the U.S. examined the impact of self-paced cycling on cognitive function in institutionalized older adults without cognitive impairment. Researchers used three cognitive assessments: Mini-Mental State Examination (MMSE), Fuld object memory evaluation, and symbol digit modality test. The study found that long-term cycling for at least 15 minutes per day in older adults without cognitive impairment had a protective effect on cognition and attention.

Cycling has also been shown to be effective adjunct therapy in certain mental health conditions.

Bicycle safety
Cycling suffers from a perception that it is unsafe. This perception is not always backed by hard numbers, because of under reporting of crashes and lack of bicycle use data (amount of cycling, kilometers cycled) which make it hard to assess the risk and monitor changes in risks. In the UK, fatality rates per mile or kilometre are slightly less than those for walking. In the US, bicycling fatality rates are less than 2/3 of those walking the same distance. However, in the UK for example the fatality and serious injury rates per hour of travel are just over double for cycling than those for walking.

Despite the risk factors associated with bicycling, cyclists have a lower overall mortality rate when compared to other groups. A Danish study in 2000 found that even after adjustment for other risk factors, including leisure time physical activity, those who did not cycle to work experienced a 39% higher mortality rate than those who did.

Injuries (to cyclists, from cycling) can be divided into two types:
 * Physical trauma (extrinsic)
 * Overuse (intrinsic)

Physical trauma
Acute physical trauma includes injuries to the head and extremities resulting from falls and collisions. Most cycle deaths result from a collision with a car or heavy goods vehicle. Drivers are at fault in the majority of these crashes. Segregated cycling infrastructure reduces the rate of crashes between bicycles and motor vehicles.

Although a majority of bicycle collisions occur during the day, bicycle lighting is recommended for safety when bicycling at night to increase visibility.

Overuse injuries
Of a study of 518 cyclists, a large majority reported at least one overuse injury, with over one third requiring medical treatment. The most common injury sites were the neck (48.8%) and the knees (41.7%), as well as the groin/buttocks (36.1%), hands (31.1%), and back (30.3%). Women were more likely to suffer from neck and shoulder pain than men.

Many cyclists suffer from overuse injuries to the knees, affecting cyclists at all levels. These are caused by many factors:
 * Incorrect bicycle fit or adjustment, particularly the saddle.
 * Incorrect adjustment of clipless pedals.
 * Too many hills, or too many miles, too early in the training season.
 * Poor training preparation for long touring rides.
 * Selecting too high a gear. A lower gear for uphill climb protects the knees, even though muscles may be well able to handle a higher gear.

Overuse injuries, including chronic nerve damage at weight bearing locations, can occur as a result of repeatedly riding a bicycle for extended periods of time. Damage to the ulnar nerve in the palm, carpal tunnel in the wrist, the genitourinary tract or bicycle seat neuropathy may result from overuse. Recumbent bicycles are designed on different ergonomic principles and eliminate pressure from the saddle and handlebars, due to the relaxed riding position.

Note that overuse is a relative term, and capacity varies greatly between individuals. Someone starting out in cycling must be careful to increase length and frequency of cycling sessions slowly, starting for example at an hour or two per day, or a hundred miles or kilometers per week. Bilateral muscular pain is a normal by-product of the training process, whereas unilateral pain may reveal "exercise-induced arterial endofibrosis". Joint pain and numbness are also early signs of overuse injury.

A Spanish study of top triathletes found those who cover more than 186 miles (300 km) a week on their bikes have less than 4% normal looking sperm, where normal adult males would be expected to have from 15% to 20%.

Saddle related
Much work has been done to investigate optimal bicycle saddle shape, size and position, and negative effects of extended use of less than optimal seats or configurations.

Excessive saddle height can cause posterior knee pain, while setting the saddle too low can cause pain in the anterior of the knee. An incorrectly fitted saddle may eventually lead to muscle imbalance. A 25 to 35-degree knee angle is recommended to avoid an overuse injury.

Although cycling is beneficial to health, men can be negatively affected by cycling more than three hours a week due to the significant weight on their perineum, an area located between the scrotum and the anus which hold some of the nerves and arteries that pass to the penis. This weight for continuous hours a week can cause men to experience numbness or tingling which can lead to them losing the ability to achieve an erection due to reduced blood flow; which 13% of males did experience in a study by Norwegian researchers who gathered data from 160 men participating in a long-distance bike tour. Fitting a proper sized seat can prevent this effect. In extreme cases, pudendal nerve entrapment can be a source of intractable perineal pain. Some cyclists with induced pudendal nerve pressure neuropathy gained relief from improvements in saddle position and riding techniques.

The National Institute for Occupational Safety and Health (NIOSH) has investigated the potential health effects of prolonged bicycling in police bicycle patrol units, including the possibility that some bicycle saddles exert excessive pressure on the urogenital area of cyclists, restricting blood flow to the genitals. Their study found that using bicycle seats without protruding noses reduced pressure on the groin by at least 65% and significantly reduced the number of cases of urogenital paresthesia. A follow-up found that 90% of bicycle officers who tried the no-nose seat were using it six months later. NIOSH recommends that riders use a no-nose bicycle seat for workplace bicycling.

Despite rumors to the contrary, there is no scientific evidence linking cycling with testicular cancer.

Exposure to air pollution
One concern is that riding in traffic may expose the cyclist to higher levels of air pollution, especially cyclists regularly traveling on or along busy roads. Some authors have claimed this to be untrue, showing that the pollutant and irritant count within cars is consistently higher, presumably because of limited circulation of air within the car and due to the air intake being directly in the stream of other traffic. Other authors have found small or inconsistent differences in concentrations but claim that exposure of cyclists is higher due to increased minute ventilation and is associated with minor biological changes. A 2010 study estimated that the gained life expectancy from the health benefits of cycling (approximately 3–14 months gained) greatly exceeded the lost life expectancy from air pollution (approximately 0.8–40 days lost). However, a systematic review comparing the effects of air pollution exposure on the health of cyclists was conducted, but the authors concluded that the differing methodologies and measuring parameters of each study made it difficult to compare results and suggested a more holistic approach was needed to accomplish this. The significance of the associated health effect, if any, is unclear but probably much smaller than the health impacts associated with accidents and the health benefits derived from additional physical activity.

title: Cycling


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Carbohydrate

A carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula C_{m}(H2O)_{n} (where m may or may not be different from n), which does not mean the H has covalent bonds with O (for example with CH2O, H has a covalent bond with C but not with O). However, not all carbohydrates conform to this precise stoichiometric definition (e.g., uronic acids, deoxy-sugars such as fucose), nor are all chemicals that do conform to this definition automatically classified as carbohydrates (e.g. formaldehyde and acetic acid).

The term is most common in biochemistry, where it is a synonym of saccharide, a group that includes sugars, starch, and cellulose. The saccharides are divided into four chemical groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides and disaccharides, the smallest (lower molecular weight) carbohydrates, are commonly referred to as sugars. While the scientific nomenclature of carbohydrates is complex, the names of the monosaccharides and disaccharides very often end in the suffix -ose, which was originally taken from the word glucose, and is used for almost all sugars, e.g. fructose (fruit sugar), sucrose (cane or beet sugar), ribose, lactose (milk sugar), etc.

Carbohydrates perform numerous roles in living organisms. Polysaccharides serve as an energy store (e.g. starch and glycogen) and as structural components (e.g. cellulose in plants and chitin in arthropods). The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g. ATP, FAD and NAD) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development.

Carbohydrates are central to nutrition and are found in a wide variety of natural and processed foods. Starch is a polysaccharide and is abundant in cereals (wheat, maize, rice), potatoes, and processed food based on cereal flour, such as bread, pizza or pasta. Sugars appear in human diet mainly as table sugar (sucrose, extracted from sugarcane or sugar beets), lactose (abundant in milk), glucose and fructose, both of which occur naturally in honey, many fruits, and some vegetables. Table sugar, milk, or honey are often added to drinks and many prepared foods such as jam, biscuits and cakes.

Cellulose, a polysaccharide found in the cell walls of all plants, is one of the main components of insoluble dietary fiber. Although it is not digestible by humans, cellulose and insoluble dietary fiber generally help maintain a healthy digestive system by facilitating bowel movements. Other polysaccharides contained in dietary fiber include resistant starch and inulin, which feed some bacteria in the microbiota of the large intestine, and are metabolized by these bacteria to yield short-chain fatty acids.

Terminology
In scientific literature, the term "carbohydrate" has many synonyms, like "sugar" (in the broad sense), "saccharide", "ose", "glucide", "hydrate of carbon" or "polyhydroxy compounds with aldehyde or ketone". Some of these terms, especially "carbohydrate" and "sugar", are also used with other meanings.

In food science and in many informal contexts, the term "carbohydrate" often means any food that is particularly rich in the complex carbohydrate starch (such as cereals, bread and pasta) or simple carbohydrates, such as sugar (found in candy, jams, and desserts). This informality is sometimes confusing since it confounds chemical structure and digestibility in humans.

Often in lists of nutritional information, such as the USDA National Nutrient Database, the term "carbohydrate" (or "carbohydrate by difference") is used for everything other than water, protein, fat, ash, and ethanol. This includes chemical compounds such as acetic or lactic acid, which are not normally considered carbohydrates. It also includes dietary fiber which is a carbohydrate but which does not contribute food energy in humans, even though it is often included in the calculation of total food energy just as though it did (i.e., as if it were a digestible and absorbable carbohydrate such as a sugar). In the strict sense, "sugar" is applied for sweet, soluble carbohydrates, many of which are used in human food.

History
The history of the discovery regarding carbohydrates dates back around 10,000 years ago in Papua New Guinea during the cultivation of Sugarcane during the Neolithic agricultural revolution. The term "carbohydrate" was first proposed by German chemist Carl Schmidt (chemist) in 1844. In 1856, glycogen, a form of carbohydrate storage in animal livers, was discovered by French physiologist Claude Bernard.

Structure
Formerly the name "carbohydrate" was used in chemistry for any compound with the formula Cm (H2O)n. Following this definition, some chemists considered formaldehyde (CH2O) to be the simplest carbohydrate, while others claimed that title for glycolaldehyde. Today, the term is generally understood in the biochemistry sense, which excludes compounds with only one or two carbons and includes many biological carbohydrates which deviate from this formula. For example, while the above representative formulas would seem to capture the commonly known carbohydrates, ubiquitous and abundant carbohydrates often deviate from this. For example, carbohydrates often display chemical groups such as: N-acetyl (e.g. chitin), sulfate (e.g. glycosaminoglycans), carboxylic acid and deoxy modifications (e.g. fucose and sialic acid).

Natural saccharides are generally built of simple carbohydrates called monosaccharides with general formula (CH2O)n where n is three or more. A typical monosaccharide has the structure H–(CHOH)x(C=O)–(CHOH)y–H, that is, an aldehyde or ketone with many hydroxyl groups added, usually one on each carbon atom that is not part of the aldehyde or ketone functional group. Examples of monosaccharides are glucose, fructose, and glyceraldehydes. However, some biological substances commonly called "monosaccharides" do not conform to this formula (e.g. uronic acids and deoxy-sugars such as fucose) and there are many chemicals that do conform to this formula but are not considered to be monosaccharides (e.g. formaldehyde CH2O and inositol (CH2O)6).

The open-chain form of a monosaccharide often coexists with a closed ring form where the aldehyde/ketone carbonyl group carbon (C=O) and hydroxyl group (–OH) react forming a hemiacetal with a new C–O–C bridge.

Monosaccharides can be linked together into what are called polysaccharides (or oligosaccharides) in a large variety of ways. Many carbohydrates contain one or more modified monosaccharide units that have had one or more groups replaced or removed. For example, deoxyribose, a component of DNA, is a modified version of ribose; chitin is composed of repeating units of N-acetyl glucosamine, a nitrogen-containing form of glucose.

Division
Carbohydrates are polyhydroxy aldehydes, ketones, alcohols, acids, their simple derivatives and their polymers having linkages of the acetal type. They may be classified according to their degree of polymerization, and may be divided initially into three principal groups, namely sugars, oligosaccharides and polysaccharides.

Monosaccharides
Monosaccharides are the simplest carbohydrates in that they cannot be hydrolyzed to smaller carbohydrates. They are aldehydes or ketones with two or more hydroxyl groups. The general chemical formula of an unmodified monosaccharide is (C•H2O)n, literally a "carbon hydrate". Monosaccharides are important fuel molecules as well as building blocks for nucleic acids. The smallest monosaccharides, for which n=3, are dihydroxyacetone and D- and L-glyceraldehydes.

Classification of monosaccharides
The α and β anomers of glucose. Note the position of the hydroxyl group (red or green) on the anomeric carbon relative to the CH2OH group bound to carbon 5: they either have identical absolute configurations (R,R or S,S) (α), or opposite absolute configurations (R,S or S,R) (β).

Monosaccharides are classified according to three different characteristics: the placement of its carbonyl group, the number of carbon atoms it contains, and its chiral handedness. If the carbonyl group is an aldehyde, the monosaccharide is an aldose; if the carbonyl group is a ketone, the monosaccharide is a ketose. Monosaccharides with three carbon atoms are called trioses, those with four are called tetroses, five are called pentoses, six are hexoses, and so on. These two systems of classification are often combined. For example, glucose is an aldohexose (a six-carbon aldehyde), ribose is an aldopentose (a five-carbon aldehyde), and fructose is a ketohexose (a six-carbon ketone).

Each carbon atom bearing a hydroxyl group (-OH), with the exception of the first and last carbons, are asymmetric, making them stereo centers with two possible configurations each (R or S). Because of this asymmetry, a number of isomers may exist for any given monosaccharide formula. Using Le Bel-van't Hoff rule, the aldohexose D-glucose, for example, has the formula (C·H2O)6, of which four of its six carbons atoms are stereogenic, making D-glucose one of 24=16 possible stereoisomers. In the case of glyceraldehydes, an aldotriose, there is one pair of possible stereoisomers, which are enantiomers and epimers. 1, 3-dihydroxyacetone, the ketose corresponding to the aldose glyceraldehydes, is a symmetric molecule with no stereo centers. The assignment of D or L is made according to the orientation of the asymmetric carbon furthest from the carbonyl group: in a standard Fischer projection if the hydroxyl group is on the right the molecule is a D sugar, otherwise it is an L sugar. The "D-" and "L-" prefixes should not be confused with "d-" or "l-", which indicate the direction that the sugar rotates plane polarized light. This usage of "d-" and "l-" is no longer followed in carbohydrate chemistry.

Ring-straight chain isomerism
The aldehyde or ketone group of a straight-chain monosaccharide will react reversibly with a hydroxyl group on a different carbon atom to form a hemiacetal or hemiketal, forming a heterocyclic ring with an oxygen bridge between two carbon atoms. Rings with five and six atoms are called furanose and pyranose forms, respectively, and exist in equilibrium with the straight-chain form.

During the conversion from straight-chain form to the cyclic form, the carbon atom containing the carbonyl oxygen, called the anomeric carbon, becomes a stereogenic center with two possible configurations: The oxygen atom may take a position either above or below the plane of the ring. The resulting possible pair of stereoisomers is called anomers. In the α anomer, the -OH substituent on the anomeric carbon rests on the opposite side (trans) of the ring from the CH2OH side branch. The alternative form, in which the CH2OH substituent and the anomeric hydroxyl are on the same side (cis) of the plane of the ring, is called the β anomer.

Use in living organisms
Monosaccharides are the major fuel source for metabolism, being used both as an energy source (glucose being the most important in nature as it is the product of photosynthesis in plants) and in biosynthesis. When monosaccharides are not immediately needed, they are often converted to more space-efficient (i.e., less water-soluble) forms, often polysaccharides. In many animals, including humans, this storage form is glycogen, especially in liver and muscle cells. In plants, starch is used for the same purpose. The most abundant carbohydrate, cellulose, is a structural component of the cell wall of plants and many forms of algae. Ribose is a component of RNA. Deoxyribose is a component of DNA. Lyxose is a component of lyxoflavin found in the human heart. Ribulose and xylulose occur in the pentose phosphate pathway. Galactose, a component of milk sugar lactose, is found in galactolipids in plant cell membranes and in glycoproteins in many tissues. Mannose occurs in human metabolism, especially in the glycosylation of certain proteins. Fructose, or fruit sugar, is found in many plants and humans, it is metabolized in the liver, absorbed directly into the intestines during digestion, and found in semen. Trehalose, a major sugar of insects, is rapidly hydrolyzed into two glucose molecules to support continuous flight.

Disaccharides

Two joined monosaccharides are called a disaccharide, the simplest kind of polysaccharide. Examples include sucrose and lactose. They are composed of two monosaccharide units bound together by a covalent bond known as a glycosidic linkage formed via a dehydration reaction, resulting in the loss of a hydrogen atom from one monosaccharide and a hydroxyl group from the other. The formula of unmodified disaccharides is C12H22O11. Although there are numerous kinds of disaccharides, a handful of disaccharides are particularly notable.

Sucrose, pictured to the right, is the most abundant disaccharide, and the main form in which carbohydrates are transported in plants. It is composed of one D-glucose molecule and one D-fructose molecule. The systematic name for sucrose, O-α-D-glucopyranosyl-(1→2)-D-fructofuranoside, indicates four things:
 * Its monosaccharides: glucose and fructose
 * Their ring types: glucose is a pyranose and fructose is a furanose
 * How they are linked together: the oxygen on carbon number 1 (C1) of α-D-glucose is linked to the C2 of D-fructose.
 * The -oside suffix indicates that the anomeric carbon of both monosaccharides participates in the glycosidic bond.

Lactose, a disaccharide composed of one D-galactose molecule and one D-glucose molecule, occurs naturally in mammalian milk. The systematic name for lactose is O-β-D-galactopyranosyl-(1→4)-D-glucopyranose. Other notable disaccharides include maltose (two D-glucoses linked α-1,4) and cellobiose (two D-glucoses linked β-1,4). Disaccharides can be classified into two types: reducing and non-reducing disaccharides. If the functional group is present in bonding with another sugar unit, it is called a reducing disaccharide or biose.

Nutrition

Carbohydrate consumed in food yields 3.87 kilocalories of energy per gram for simple sugars, and 3.57 to 4.12 kilocalories per gram for complex carbohydrate in most other foods. Relatively high levels of carbohydrate are associated with processed foods or refined foods made from plants, including sweets, cookies and candy, table sugar, honey, soft drinks, breads and crackers, jams and fruit products, pastas and breakfast cereals. Lower amounts of digestible carbohydrate are usually associated with unrefined foods as these foods have more fiber, including beans, tubers, rice, and unrefined fruit. Animal-based foods generally have the lowest carbohydrate levels, although milk does contain a high proportion of lactose.

Organisms typically cannot metabolize all types of carbohydrate to yield energy. Glucose is a nearly universal and accessible source of energy. Many organisms also have the ability to metabolize other monosaccharides and disaccharides but glucose is often metabolized first. In Escherichia coli, for example, the lac operon will express enzymes for the digestion of lactose when it is present, but if both lactose and glucose are present the lac operon is repressed, resulting in the glucose being used first (see: Diauxie). Polysaccharides are also common sources of energy. Many organisms can easily break down starches into glucose; most organisms, however, cannot metabolize cellulose or other polysaccharides like chitin and arabinoxylans. These carbohydrate types can be metabolized by some bacteria and protists. Ruminants and termites, for example, use microorganisms to process cellulose. Even though these complex carbohydrates are not very digestible, they represent an important dietary element for humans, called dietary fiber. Fiber enhances digestion, among other benefits.

The Institute of Medicine recommends that American and Canadian adults get between 45 and 65% of dietary energy from whole-grain carbohydrates. The Food and Agriculture Organization and World Health Organization jointly recommend that national dietary guidelines set a goal of 55–75% of total energy from carbohydrates, but only 10% directly from sugars (their term for simple carbohydrates). A 2017 Cochrane Systematic Review concluded that there was insufficient evidence to support the claim that whole grain diets can affect cardiovascular disease.

Classification
Nutritionists often refer to carbohydrates as either simple or complex. However, the exact distinction between these groups can be ambiguous. The term complex carbohydrate was first used in the U.S. Senate Select Committee on Nutrition and Human Needs publication Dietary Goals for the United States (1977) where it was intended to distinguish sugars from other carbohydrates (which were perceived to be nutritionally superior). However, the report put "fruit, vegetables and whole-grains" in the complex carbohydrate column, despite the fact that these may contain sugars as well as polysaccharides. This confusion persists as today some nutritionists use the term complex carbohydrate to refer to any sort of digestible saccharide present in a whole food, where fiber, vitamins and minerals are also found (as opposed to processed carbohydrates, which provide energy but few other nutrients). The standard usage, however, is to classify carbohydrates chemically: simple if they are sugars (monosaccharides and disaccharides) and complex if they are polysaccharides (or oligosaccharides).

In any case, the simple vs. complex chemical distinction has little value for determining the nutritional quality of carbohydrates. Some simple carbohydrates (e.g. fructose) raise blood glucose rapidly, while some complex carbohydrates (starches), raise blood sugar slowly. The speed of digestion is determined by a variety of factors including which other nutrients are consumed with the carbohydrate, how the food is prepared, individual differences in metabolism, and the chemistry of the carbohydrate. Carbohydrates are sometimes divided into "available carbohydrates", which are absorbed in the small intestine and "unavailable carbohydrates", which pass to the large intestine, where they are subject to fermentation by the gastrointestinal microbiota.

The USDA's Dietary Guidelines for Americans 2010 call for moderate- to high-carbohydrate consumption from a balanced diet that includes six one-ounce servings of grain foods each day, at least half from whole grain sources and the rest are from enriched.

The glycemic index (GI) and glycemic load concepts have been developed to characterize food behavior during human digestion. They rank carbohydrate-rich foods based on the rapidity and magnitude of their effect on blood glucose levels. Glycemic index is a measure of how quickly food glucose is absorbed, while glycemic load is a measure of the total absorbable glucose in foods. The insulin index is a similar, more recent classification method that ranks foods based on their effects on blood insulin levels, which are caused by glucose (or starch) and some amino acids in food.

Health effects of dietary carbohydrate restriction
Low-carbohydrate diets may miss the health advantages – such as increased intake of dietary fiber – afforded by high-quality carbohydrates found in legumes and pulses, whole grains, fruits, and vegetables. A "meta-analysis, of moderate quality," included as adverse effects of the diet halitosis, headache and constipation.

Carbohydrate-restricted diets can be as effective as low-fat diets in helping achieve weight loss over the short term when overall calorie intake is reduced. An Endocrine Society scientific statement said that "when calorie intake is held constant [...] body-fat accumulation does not appear to be affected by even very pronounced changes in the amount of fat vs carbohydrate in the diet." In the long term, effective weight loss or maintenance depends on calorie restriction, not the ratio of macronutrients in a diet. The reasoning of diet advocates that carbohydrates cause undue fat accumulation by increasing blood insulin levels, and that low-carbohydrate diets have a "metabolic advantage", is not supported by clinical evidence. Further, it is not clear how low-carbohydrate dieting affects cardiovascular health, although two reviews showed that carbohydrate restriction may improve lipid markers of cardiovascular disease risk.

Carbohydrate-restricted diets are no more effective than a conventional healthy diet in preventing the onset of type 2 diabetes, but for people with type 2 diabetes, they are a viable option for losing weight or helping with glycemic control. There is limited evidence to support routine use of low-carbohydrate dieting in managing type 1 diabetes. The American Diabetes Association recommends that people with diabetes should adopt a generally healthy diet, rather than a diet focused on carbohydrate or other macronutrients.

An extreme form of low-carbohydrate diet – the ketogenic diet – is established as a medical diet for treating epilepsy. Through celebrity endorsement during the early 21st century, it became a fad diet as a means of weight loss, but with risks of undesirable side effects, such as low energy levels and increased hunger, insomnia, nausea, and gastrointestinal discomfort. The British Dietetic Association named it one of the "top 5 worst celeb diets to avoid in 2018".

Metabolism
Carbohydrate metabolism is the series of biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms.

The most important carbohydrate is glucose, a simple sugar (monosaccharide) that is metabolized by nearly all known organisms. Glucose and other carbohydrates are part of a wide variety of metabolic pathways across species: plants synthesize carbohydrates from carbon dioxide and water by photosynthesis storing the absorbed energy internally, often in the form of starch or lipids. Plant components are consumed by animals and fungi, and used as fuel for cellular respiration. Oxidation of one gram of carbohydrate yields approximately 16 kJ (4 kcal) of energy, while the oxidation of one gram of lipids yields about 38 kJ (9 kcal). The human body stores between 300 and 500 g of carbohydrates depending on body weight, with the skeletal muscle contributing to a large portion of the storage. Energy obtained from metabolism (e.g., oxidation of glucose) is usually stored temporarily within cells in the form of ATP. Organisms capable of anaerobic and aerobic respiration metabolize glucose and oxygen (aerobic) to release energy, with carbon dioxide and water as byproducts.

Catabolism
Catabolism is the metabolic reaction which cells undergo to break down larger molecules, extracting energy. There are two major metabolic pathways of monosaccharide catabolism: glycolysis and the citric acid cycle.

In glycolysis, oligo- and polysaccharides are cleaved first to smaller monosaccharides by enzymes called glycoside hydrolases. The monosaccharide units can then enter into monosaccharide catabolism. A 2 ATP investment is required in the early steps of glycolysis to phosphorylate Glucose to Glucose 6-Phosphate (G6P) and Fructose 6-Phosphate (F6P) to Fructose 1,6-biphosphate (FBP), thereby pushing the reaction forward irreversibly. In some cases, as with humans, not all carbohydrate types are usable as the digestive and metabolic enzymes necessary are not present.

Carbohydrate chemistry
Carbohydrate chemistry is a large and economically important branch of organic chemistry. Some of the main organic reactions that involve carbohydrates are:
 * Amadori rearrangement
 * Carbohydrate acetalisation
 * Carbohydrate digestion
 * Cyanohydrin reaction
 * Koenigs–Knorr reaction
 * Lobry de Bruyn–Van Ekenstein transformation
 * Nef reaction
 * Wohl degradation

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title: Carbohydrate


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CSS Virginia

CSS Virginia was the first steam-powered ironclad warship built by the Confederate States Navy during the first year of the American Civil War; she was constructed as a casemate ironclad using the razéed (cut down) original lower hull and engines of the scuttled steam frigate USS Merrimack (1855). Virginia was one of the participants in the Battle of Hampton Roads, opposing the Union's USS Monitor in March 1862. The battle is chiefly significant in naval history as the first battle between ironclads.

USS Merrimack becomes CSS Virginia
When the Commonwealth of Virginia seceded from the Union in 1861, one of the important US military bases threatened was Gosport Navy Yard (now Norfolk Naval Shipyard) in Portsmouth, Virginia. Accordingly, orders were sent to destroy the base rather than allow it to fall into Confederate hands. On the afternoon of 17 April, the day Virginia seceded, Engineer in Chief B. F. Isherwood managed to get the frigate's engines lit. However, the previous night secessionists had sunk light boats between Craney Island and Sewell's Point, blocking the channel. On 20 April, before evacuating the Navy Yard, the U. S. Navy burned Merrimack to the waterline and sank her to preclude capture. When the Confederate government took possession of the fully provisioned yard, the base's new commander, Flag Officer French Forrest, contracted on May 18 to salvage the wreck of the frigate. This was completed by May 30, and she was towed into the shipyard's only dry dock (today known as Drydock Number One), where the burned structures were removed.

The wreck was surveyed and her lower hull and machinery were discovered to be undamaged. Stephen Mallory, Secretary of the Navy decided to convert Merrimack into an ironclad, since she was the only large ship with intact engines available in the Chesapeake Bay area. Preliminary sketch designs were submitted by Lieutenants John Mercer Brooke and John L. Porter, each of whom envisaged the ship as a casemate ironclad. Brooke's general design showed the bow and stern portions submerged, and his design was the one finally selected. The detailed design work would be completed by Porter, who was a trained naval constructor. Porter had overall responsibility for the conversion, but Brooke was responsible for her iron plate and heavy ordnance, while William P. Williamson, Chief Engineer of the Navy, was responsible for the ship's machinery.

Reconstruction as an ironclad
The hull's burned timbers were cut down past the vessel's original waterline, leaving just enough clearance to accommodate her large, twin-bladed screw propeller. A new fantail and armored casemate were built atop a new main deck, and a v-shaped (bulwark) was added to her bow, which attached to the armored casemate. This forward and aft main deck and fantail were designed to stay submerged and were covered in 4 in iron plate, built up in two layers. The casemate was built of 24 in of oak and pine in several layers, topped with two 2 in layers of iron plating oriented perpendicular to each other, and angled at 36 degrees from horizontal to deflect fired enemy shells.

From reports in Northern newspapers, Virginia's designers were aware of the Union plans to build an ironclad and assumed their similar ordnance would be unable to do much serious damage to such a ship. It was decided to equip their ironclad with a ram, an anachronism on a 19th-century warship. Merrimack's steam engines, now part of Virginia, were in poor working order; they had been slated for replacement when the decision was made to abandon the Norfolk naval yard. The salty Elizabeth River water and the addition of tons of iron armor and pig iron ballast, added to the hull's unused spaces for needed stability after her initial refloat, and to submerge her unarmored lower levels, only added to her engines' propulsion issues. As completed, Virginia had a turning radius of about 1 mi and required 45 minutes to complete a full circle, which would later prove to be a major handicap in battle with the far more nimble Monitor.

The ironclad's casemate had 14 gun ports, three each in the bow and stern, one firing directly along the ship's centerline, the two others angled at 45° from the center line; these six bow and stern gun ports had exterior iron shutters installed to protect their cannon. There were four gun ports on each broadside; their protective iron shutters remained uninstalled during both days of the Battle of Hampton Roads. Virginia's battery consisted of four muzzle-loading single-banded Brooke rifles and six smoothbore 9 in Dahlgren guns salvaged from the old Merrimack. Two of the rifles, the bow and stern pivot guns, were 7 in caliber and weighed 14500 lb each. They fired a 104 lb shell. The other two were 6.4 in cannon of about 9100 lb, one on each broadside. The 9-inch Dahlgrens were mounted three to a side; each weighed approximately 9200 lb and could fire a 72.5 lb shell up to a range of 3357 yd (or 1.9 miles) at an elevation of 15°. Both amidship Dahlgrens nearest the boiler furnaces were fitted-out to fire heated shot. On her upper casemate deck were positioned two anti-boarding/personnel 12-pounder Howitzers.

Virginia's commanding officer, Flag Officer Franklin Buchanan, arrived to take command only a few days before her first sortie; the ironclad was placed in commission and equipped by her executive officer, Lieutenant Catesby ap Roger Jones.

Battle of Hampton Roads

The Battle of Hampton Roads began on March 8, 1862, when Virginia engaged the blockading Union fleet. Despite an all-out effort to complete her, the new ironclad still had workmen on board when she sailed into Hampton Roads with her flotilla of five CSN support ships: CSS Raleigh (serving as Virginia's tender) and CSS Beaufort, CSS Patrick Henry, CSS Jamestown, and CSS Teaser.

The first Union ship to be engaged by Virginia was the all-wood, sail-powered USS Cumberland (1842), which was first crippled during a furious cannon exchange, and then rammed in her forward starboard bow by Virginia. As Cumberland began to sink, the port side half of Virginia's iron ram was broken off, causing a bow leak in the ironclad. Seeing what had happened to Cumberland, the captain of USS Congress (1841) ordered his frigate into shallower water, where she soon grounded. Congress and Virginia traded cannon fire for an hour, after which the badly-damaged Congress finally surrendered. While the surviving crewmen of Congress were being ferried off the ship, a Union battery on the north shore opened fire on Virginia. Outraged at such a breach of war protocol, in retaliation Virginias now angry captain, Commodore Franklin Buchanan, gave the order to open fire with hot-shot on the surrendered Congress as he rushed to Virginias exposed upper casemate deck, where he was injured by enemy rifle fire. Congress, now set ablaze by the retaliatory shelling, burned for many hours into the night, a symbol of Confederate naval power and a costly wake-up call for the all-wood Union blockading squadron.

Virginia did not emerge from the battle unscathed, however. Her hanging port side anchor was lost after ramming Cumberland; the bow was leaking from the loss of the ram's port side half; shot from Cumberland, Congress, and the shore-based Union batteries had riddled her smokestack, reducing her boilers' draft and already slow speed; two of her broadside cannon (without shutters) were put out of commission by shell hits; a number of her armor plates had been loosened; both of Virginia's 22 ft cutters had been shot away, as had both 12-pounder anti-boarding/anti-personnel howitzers, most of the deck stanchions, railings, and both flagstaffs. Even so, the now-injured Buchanan ordered an attack on USS Minnesota (1855), which had run aground on a sandbar trying to escape Virginia. However, because of the ironclad's 22 ft draft (fully loaded), she was unable to get close enough to do any significant damage. It being late in the day, Virginia retired from the conflict with the expectation of returning the next day and completing the destruction of the remaining Union blockaders.

Later that night, USS Monitor arrived at Union-held Fort Monroe. She had been rushed to Hampton Roads, still not quite complete, all the way from the Brooklyn Navy Yard, in hopes of defending the force of wooden ships and preventing "the rebel monster" from further threatening the Union's blockading fleet and nearby cities, like Washington, D.C. While under tow, she nearly foundered twice during heavy storms on her voyage south, arriving in Hampton Roads by the bright firelight from the still-burning triumph of Virginia's first day of handiwork.

The next day, on March 9, 1862, the world's first battle between ironclads took place. The smaller, nimbler, and faster Monitor was able to outmaneuver the larger, slower Virginia, but neither ship proved able to do any severe damage to the other, despite numerous shell hits by both combatants, many fired at virtually point-blank range. Monitor had a much lower freeboard and only its single, rotating, two-cannon gun turret and forward pilothouse sitting above her deck, and thus was much harder to hit with Virginia's heavy cannon. After hours of shell exchanges, Monitor finally retreated into shallower water after a direct shell hit to her armored pilothouse forced her away from the conflict to assess the damage. The captain of the Monitor, Lieutenant John L. Worden, had taken a direct gunpowder explosion to his face and eyes, blinding him, while looking through the pilothouse's narrow, horizontal viewing slits. Monitor remained in the shallows, but as it was late in the day, Virginia steamed for her home port, the battle ending without a clear victor. The captain of Virginia that day, Lieutenant Catesby ap Roger Jones, received advice from his pilots to depart over the sandbar toward Norfolk until the next day. Lieutenant Jones wanted to continue the fight, but the pilots emphasized that the Virginia had "nearly three miles to run to the bar" and that she could not remain and "take the ground on a falling tide." To prevent running aground, Lieutenant Jones reluctantly moved the ironclad back toward port. Virginia retired to the Gosport Naval Yard at Portsmouth, Virginia, and remained in drydock for repairs until April 4, 1862.

In the following month, the crew of Virginia were unsuccessful in their attempts to break the Union blockade. The blockade had been bolstered by the hastily ram-fitted paddle steamer USS Vanderbilt (1862), and SS Illinois as well as the SS Arago (1855) and USS Minnesota (1855), which had been repaired. Virginia made several sorties back over to Hampton Roads hoping to draw Monitor into battle. Monitor, however, was under strict orders not to re-engage; the two combatants would never battle again.

On April 11, the Confederate Navy sent Lieutenant Joseph Nicholson Barney, in command of the paddle side-wheeler CSS Jamestown, along with Virginia and five other ships in full view of the Union squadron, enticing them to fight. When it became clear that Union Navy ships were unwilling to fight, the CS Navy squadron moved in and captured three merchant ships, the brigs Marcus and Sabout and the schooner Catherine T. Dix. Their ensigns were then hoisted "Union-side down" to further taunt the Union Navy into a fight, as they were towed back to Norfolk, with the help of CSS Raleigh.

By late April, the new Union ironclads USRC E. A. Stevens and USS Galena (1862) had also joined the blockade. On May 8, 1862, Virginia and the James River Squadron ventured out when the Union ships began shelling the Confederate fortifications near Norfolk, but the Union ships retired under the shore batteries on the north side of the James River and on Rip Raps island.

Destruction

On May 10, 1862, advancing Union troops occupied Norfolk. Since Virginia was now a steam-powered heavy battery and no longer an ocean-going cruiser, her pilots judged her not seaworthy enough to enter the Atlantic, even if she were able to pass the Union blockade. Virginia was also unable to retreat further up the James River due to her deep 22 ft draft (fully loaded). In an attempt to reduce it, supplies and coal were dumped overboard, even though this exposed the ironclad's unarmored lower hull, this was still not enough to make a difference. Without a home port and no place to go, Virginia's new captain, flag officer Josiah Tattnall III, reluctantly ordered her destruction in order to keep the ironclad from being captured. The ship was destroyed by Catesby Jones and John Taylor Wood, who set fire to scattered gunpowder and cotton strewn across the ship's deck. Early on the morning of May 11, 1862, off Craney Island, the fire reached the ironclad's magazine, leading to a massive explosion that obliterated the ship. What remained of the Virginia then sank to the harbor floor.

After the war, the government determined that the wreck of the Virginia needed to be removed from the channel. In 1867, Captain D. A. Underdown salvaged 290,000 pounds of iron from the site, much of which was taken from the ship's ram and cannons. The following year, Underdown detonated explosives under the Virginia 's hulk to fully clear the river, but the attempt did not totally remove the wreck. In 1871, E.J. Griffith recovered an additional 102,883 pounds of iron from the seabed, and in 1876, the "remaining timbers" of the ship were raised. In 1982, the National Underwater and Marine Agency explored the area around Craney Island and found that "there are no large areas of either concentrated or scattered debris associated with the Virginia lying on the river bottom within the survey area."

Most of the recovered iron was melted down and sold for scrap (notably, some of the ship's iron was used to craft Pokahuntas Bell in 1907.) Other pieces of the ship have been preserved in museums: The ship's brass bell is held at the Hampton Roads Naval Museum, and one of the Virginia 's anchors now rests in front of the American Civil War Museum in Richmond. Numerous souvenirs, ostensibly made from salvaged iron and wood raised from Virginia's sunken hulk, have found a ready and willing market among Civil War enthusiasts and eastern seaboard residents. However, the provenance of many of these artifacts is impossible to prove, which has given rise to the humorous adage that "if you took all the iron and all the wood supposedly collected from the [wreck of the CSS Virginia], you'd have enough to outfit a fleet of ironclads."

Historical names
Although the Confederacy renamed the ship, she is still frequently referred to by her Union name. When she was first commissioned into the United States Navy in 1856, her name was Merrimack, with the K; the name was derived from the Merrimack River near where she was built. She was the second ship of the U. S. Navy to be named for the Merrimack River, which is formed by the confluence of the Pemigewasset and Winnipesaukee rivers at Franklin, New Hampshire. The Merrimack flows south across New Hampshire, then eastward across northeastern Massachusetts before finally emptying in the Atlantic at Newburyport, Massachusetts.

After raising, restoring, and outfitting as an ironclad warship, the Confederacy bestowed on her the name Virginia. Nonetheless, the Union continued to refer to the Confederate ironclad by either its original name, Merrimack, or by the nickname "The Rebel Monster". In the aftermath of the Battle of Hampton Roads, the names Virginia and Merrimack were used interchangeably by both sides, as attested to by various newspapers and correspondence of the day. Navy reports and pre-1900 historians frequently misspelled the name as "Merrimac", which was actually an unrelated ship, hence "the Battle of the Monitor and the Merrimac". Both spellings are still in use in the Hampton Roads area.

Memorial, heritage

 * A large exhibit at the Jamestown Exposition held in 1907 at Sewell's Point was the "Battle of the Merrimac and Monitor," a large diorama that was housed in a special building.
 * A small community in Montgomery County, Virginia, near where the coal burned by the Confederate ironclad was mined, is now known as Merrimac.

 * The name of the Monitor-Merrimac Memorial Bridge-Tunnel, built in Hampton Roads in the general vicinity of the famous engagement, with both Virginia and federal funds.

title: CSS Virginia


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Canon

Canon or Canons may refer to:

Arts and entertainment

 * Canon (fiction), the material accepted as officially written by an author or an ascribed author
 * Literary canon, an accepted body of works considered as high culture
 * Western canon, the body of high culture literature, music, philosophy, and works of art that is highly valued in the West
 * Canon of proportions, a formally codified set of criteria deemed mandatory for a particular artistic style of figurative art
 * Canon (music), a type of composition
 * Canon (hymnography), a type of hymn used in Eastern Orthodox Christianity.
 * Canon (album), a 2007 album by Ani DiFranco
 * Canon (film), a 1964 Canadian animated short
 * Canon (game), an online browser-based strategy war game
 * Canon (manga), by Nikki
 * Canonical plays of William Shakespeare
 * The Canon (Natalie Angier book), a 2007 science book by Natalie Angier
 * The Canon (podcast), concerning film
 * The Cannons, an indie band

Brands and enterprises

 * Canon Inc., a Japanese imaging and optical products corporation
 * Château Canon (disambiguation), a number of wineries
 * UBM Canon, a media company headquartered in Los Angeles

People

 * Canon (rapper) (born Aaron McCain, 1989)
 * Fernando Canon (1860–1938), Filipino revolutionary general, poet, inventor, engineer, musician and chess player
 * Lou Canon, stage name of Leanne Greyerbiehl, a Canadian indie pop singer-songwriter

Places

 * Canon, Georgia, United States
 * Canons Park, London, United Kingdom
 * Canon Row, a street in Westminster, London
 * Cañon City, Colorado, United States
 * Cañon Fiord, on Ellesmere Island in Nunavut, Canada
 * Canon Rock, an island in Northern Ireland

Religion

 * : some religious texts are accepted or categorized as canonical, some non-canonical, and others extracanonical, semi-canonical, deutero-canonical, pre-canonical or post-canonical
 * Biblical canon, a set of texts regarded by a Christian or Jewish community as part of the Bible
 * Canon law, the whole judicial system in Christian churches
 * Canon (canon law), a law or ordinance promulgated by a synod, ecumenical council, or individual bishop (within the canon law system of that Church).
 * Canon (clergy), a title of certain Christian priests
 * Canon regular, a priest who lives in community under a rule
 * Canon (hymnography), a kind of hymn in Eastern Orthodox Christianity
 * Pāli Canon, scriptures of Theravāda Buddhism (these include the Sutta Pitaka, the Vinaya Pitaka and the Abhidhamma Pitaka)

Other uses

 * Canon (basic principle), an accepted body of rules
 * Canon, in bellfounding, one or more hanging loops cast integrally with the crown
 * The Canon of Medicine, a 1025 CE medical encyclopedia by Ibn Sīnā (Avicenna)
 * Canon Yaoundé, a Cameroonian association football club based in the capital city of Yaoundé
 * Canons High School, Edgware, Greater London

title: Canon