People who participate in sports are more likely than others of the same age to have muscle and tendon injuries and bone fractures. This certainly doesn't mean you should avoid sports - the health benefits far outweigh the cost in terms of sports injuries.
Sports injuries are most commonly caused by poor training methods, structural abnormalities, weakness in muscles, tendons, ligaments, and unsafe exercising environments. The most common cause of injury is poor training. For example, muscles need 48 hours to recover after a workout. Increasing exercise intensity too quickly and not stopping when pain develops while exercising also causes injury.
Everyone's bone architecture is a little different, and almost all of us have one or two weak points where the arrangement of bone and muscle leaves us prone to injury. In injuries to the ankles, legs, knees and hips, for instance, common predisposing factors are:
uneven leg length
excessive pronation (flat feet)
cavus foot (over-high arches)
bowlegged or knock-knee alignment
Uneven leg length may lead to awkward running and increases the chance of injury, but many people with equal-length legs suffer the same effects by running on tilted running tracks or along the side of a road that is higher in the center. The hip of the leg that strikes the higher surface will suffer more strain.
Pronation is the inward rolling of the foot after the heel strikes the ground, before the weight is shifted forward to the ball of the foot. By rolling inwards, the foot spreads the shock of impact with the ground. If it rolls too easily, however, it can place uneven stress on muscles and ligaments higher in the leg.
While an overly flexible ankle and foot can cause excessive pronation, a too-rigid ankle will cause the effects of cavus foot. Although the arch of the foot itself may be normal, it appears very high because the foot doesn't flatten inwards when weight is placed on it. Such feet are poor shock absorbers and increase the risk of fractures higher in the legs.
Bowlegs or knock knees add extra stress through knees and ankles over time, and may make ankle sprains more likely.
Other structural conditions that make sports injuries more common include:
lumbar lordosis - forward curve in the lower spine
forward tilted pelvis
patella alta - a kneecap that's higher than usual
high Q angle - kneecap displaced to one side, as with knock knees
Having some muscles that are very strong and others that are weak can lead to injury. If your quadriceps (front thigh muscles) are very strong, it can increase the risk of a stretched or torn hamstring (rear thigh muscle). Tight iliotibial bands may be the cause of knee pain for many athletes in running sports.
Overuse injuries are caused by repeated, microscopic injuries to a part of the body. Many long distance runners experience overuse injuries even after years of running. For road runners, the surface is hard and sometimes uneven, and the running movements are repetitive. In addition, there are usually both up- and downhill elements, and these increase the stress on tendons and muscles in the lower leg. You will more likely develop running injuries if you wear the wrong shoes or sneakers. You should use footwear that doesn't allow side-to-side movement of the heel, and that adequately cushions the foot.
People who play racket sports tend to injure their upper body. The need to firmly grasp the racket and the shock of impact with the ball can cause various injuries to the tendons of the wrist and elbow, such as "tennis elbow," which may extend into the muscles of the forearm. In addition, the human arm really isn't designed to handle strenuous activity above the head. Tennis is a leading cause of rotator cuff (shoulder joint) tendinitis. This is potentially one of the most difficult sports injuries. If you continue to play tennis when you have a sore shoulder, the rotator cuff tendons can fray or tear and may require surgery.