Section 1. Fundamentals

Chapter 6. Exercise and Fitness

Topics: Introduction | Benefits of Exercise | Starting an Exercise Program | Preventing Injury | Choosing the Right Exercise

Preventing Injury

More than 6 out of 10 people who start an exercise program drop out in the first 6 weeks, often because of an injury. Injuries can be prevented by scheduling workouts 48 hours apart, as described above. In addition, people should stop exercising immediately if they feel pain.

Two types of muscle discomfort may be felt after exercise. The desirable type, delayed-onset muscle soreness, does not start until several hours after exercising intensely. Usually it affects both sides of the body equally, goes away 48 hours later, and feels better after the warm-up for the next workout. The undesirable type, in which pain indicates injury, is usually felt soon after it occurs, is worse on one side of the body, does not disappear 48 hours later, and becomes much more severe if a person tries to exercise.

Injury is best prevented by warming up the muscles before exercising, followed by stretching and cooling down after exercising.

Warming Up: Starting exercise at lower intensity (for example, walking rather than running or using lighter weights) raises the temperature of muscles by increasing blood flow. Warm muscles are more pliable and less likely to tear than cold muscles, which contract sluggishly. Therefore, warming up helps prevent injuries.

Stretching: Stretching lengthens muscles and tendons, and thereby improves flexibility. Longer muscles can generate more force around joints, helping a person jump higher, lift heavier weights, run faster, and throw farther. However, stretching, unlike exercising against resistance (as in weight training), does not strengthen muscles. There is scant evidence that stretching prevents injuries or delayed-onset muscle soreness, which is caused by muscle fiber damage. A person should stretch only after warming up or exercising, when the muscles are warm and less likely to tear.

Cooling Down: Slowing down gradually (cooling down) at the end of exercise helps prevent dizziness. When the leg muscles relax, blood collects (pools) in the veins near them. To return the blood toward the heart, the leg muscles must contract. When exercise is suddenly stopped, blood pools in the legs and not enough blood goes to the brain, causing dizziness. By preventing blood from pooling, cooling down also helps the bloodstream to speed up its removal of lactic acid, a waste product that builds up in the muscles after exercise. Lactic acid does not cause delayed-onset muscle soreness, so cooling down does not prevent this soreness.