In a sport that requires the participant to maneuver relatively fragile, lightweight machines at high speeds, the injuries sustained by cyclists range from those caused by overexertion, to those incurred in dramatic, high-speed collisions, sustaining traumas that severely impair the cyclist's health.
All forms of bicycle racing carry the risk of an injury caused by the forces generated through the mechanics of pedaling a bicycle. Each of the three varieties of cycling racing creates a risk of injury specific to the event. Cycling racing may be one of road racing, which is conducted as either a single-day competition on a road course circuit, or as a multi-day stage race, such as the Tour de France. Road racing in either format places a premium on the athlete's endurance, generating significant stresses on the cardiovascular and respiratory systems, as the races may last from four to six hours in length per day. The races are often conducted in very warm or humid conditions. Road racing also requires an ability to generate shorter, very powerful bursts of energy to sprint for position or to climb hills. Road racers do not alter their posture on the bicycle from a seated position, except to stretch or, depending upon the technique employed, to sprint or to climb hills. Racers commonly find themselves in a group of riders, universally known as a peloton, which in an elite road race may be moving at speeds in excess of 25 mph (40 km/h). A single jostling between two riders in these circumstances can lead to a multiple bicycle/racer collision. The riders may also be in close quarters as they descend hills sufficiently steep that the cyclists often achieve speeds of 60 mph (100 km/hour) or more.
Mountain bike races typically take place on rugged outdoor trails and involve significant changes in elevation. High-speed collisions between the competitor and trees, rocks, and other natural obstructions are common: as an outdoor event contested in summer climates, heat, rain, and wind are all potential injury factors. Unlike the relatively smooth ride of a road-racing bicycle, the ride of a mountain bike generates significant forces upon the body of the racer. The rider is required to change position frequently, to both absorb the shocks of the ride and to achieve optimum aerodynamic effect when available.
In terms of environmental impact upon the athlete, track racing is the most sterile form of cycling. Conducted in facilities known as velodromes, which are most often a covered or enclosed oval racing facility, the speed of the racers and the banked nature of the tracks create a physical risk for the athlete.
The cycling injuries that arise in all three types of competition are those that involve the skin, the legs, and the head.
"Road rash" is the universal euphemism for the abrasion damage done to cyclists' skin when they slide or are dragged along the riding surface on a fall. A common mechanism for this injury is a missed turn, causing the bicycle wheels to lose contact with the surface. The damage caused by road rash is often magnified due to foreign particles being forced into the surface of the skin, including road tar and oils, which can lead to infection.
Leg injuries can occur to any of the muscles, tendons, or ligaments that are involved in the production of power or the resistance applied by the stroke of the pedal. Common leg injuries are muscle strains, particularly in the gastrocnemius (calf muscle) or the quadriceps (thigh muscle). Knee strains are often caused by either the repetitive nature of pedaling, or by tightness in the illiol band, which runs from the knee joint to the hip, due to muscle imbalances in the thigh. Tendonitis in both the patellar (knee cap) tendon and the Achilles tendon similarly result.
Head injuries in cycling occur in two circumstances. Notwithstanding the speeds that cyclists achieve in competition, both through the application of their own muscle power and as a result of the effect of gravity in the descents on steep hills, many cyclists do not wear adequate helmet protection. The human head striking pavement or a fixed object such as a tree branch creates a serious risk of permanent injury or death for the rider. Similarly, the speed generated places the cyclist at risk of being struck in the face by flying insects that can cause damage to the skin or eyes. Given the amount of time spent outdoors, cycling also presents a greater than usual risk of overexposure to the sun.
Road racers are particularly vulnerable to heat-induced injuries, due to both the existing environmental factors, as well as their exposure to the reflective heat from paved road surfaces. Dehydration and a resultant loss of electrolytes essential to proper bodily functions is a risk in this aspect of the sport, which commonly lead to potential heat exhaustion or heat stroke. When the rider is consuming fluids, but is not attentive to sodium levels, the debilitating condition known as hyponatremia may occur.
Mountain bikers are exposed to a considerably greater degree of force to be absorbed by their bodies through the contact between the bicycle and the terrain of the race course. Much of this force is absorbed in the hands, through the vibration of the handle bars, which can lead to a variety of strain injuries to the muscles ranging from those in the wrist to those in the shoulder. Mountain biking also presents a risk of contact with outdoor allergens such as poison ivy and poison oak.
Successful track racing places a greater emphasis upon explosive leg action than either road or mountain bike racing. Injuries that often result from a single movement, such as Achilles tendon ruptures and hamstring tears, are more prevalent in track cycling.