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Benefits
The physical exercise gained from cycling is generally linked with increased health and well-being. According to the World Health Organization, physical inactivity is second only to tobacco smoking as a health risk in developed countries, and this is associated with many tens of billions of dollars of healthcare costs. The WHO's 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. In this regard, 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.
Interestingly, it has been found that despite toning the leg muscles, cycling actually causes buttocks to lose tone and muscle.
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 due to the low impact that it has on the joints. In particular cycling is commonly used within knee rehabilitation programs.
Injuries
Cycling is seen by some to be an inherently high-risk, dangerous activity although use of appropriate safety equipment can reduce risk of serious injury. In the UK, fatality rates per mile or kilometer are slightly less than those for walking. In the US, bicycling fatality rates are less than 2/3 of those walking the same distance. For a child cyclist the rate per mile or kilometer travelled is around 55 times that for a child occupant of a car, while the fatality and serious injury rates per hour of travel are just over double for cycling than for walking (due to the reduced travel time), in the UK. It should be noted that calculated fatality rates based on distance for bicycling (as well as for walking) can have an exceptionally large margin of error, since there are generally no annual registrations or odometers required for bicycles (as there are with motor vehicles), and this means the distance traveled must be estimated.
Most cycle deaths result from a collision with a car or heavy goods vehicle. However, a very high proportion of non-fatal injuries to cyclists do not involve any other person or vehicle.
A Danish study in 2000 concluded that "bicycling to work decreased risk of mortality in approximately 40% after multivariate adjustment, including leisure time physical activity". This conclusion is open to various interpretations.
Injuries (to cyclists, from cycling) can be divided into two types:
• Physical trauma (extrinsic)
• Overuse (intrinsic).
Acute physical trauma includes injuries to the head and extremities resulting from falls and collisions. Since a large percentage of the collisions between motor and pedal vehicles occur at night, bicycle lighting is required for safety when bicycling at night.
The most common cycling overuse injury occurs in 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 your muscles are well able to handle a higher gear.
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.
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. Muscular pain is a normal by-product of the training process, but joint pain and numbness are early signs of overuse injury.
Cycling has been linked to sexual impotence due to pressure on the perineum from the seat, but fitting a proper sized seat prevents 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. NIOSH is investigating whether saddles developed without protruding noses (which remove the pressure from the urogenital area) will alleviate any potential health problems.
Despite rumors to the contrary, there is no scientific evidence linking cycling with testicular cancer in men.
Andy Pruitt, director of the Boulder Center for Sports Medicine, wrote a book about diagnosing, treating, and preventing cycling-related injuries. Andy Pruitt's Complete Medical Guide for Cyclists
Air pollution
One concern often expressed (both by non-cyclists and some cyclists) is the thought that riding in traffic exposes the cyclist to higher levels of air pollution, especially if he travels on or along busy roads. This has been shown to be untrue, as 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).
