Competitive running or high-impact aerobics pose a high risk for a number of injuries in the bones and muscle. The effect of high-impact exercise on the back is not entirely clear. Some research suggests that over time, it may increase the risk for degenerative disk disease. A survey of people who played tennis, however, found no increased risk for low back pain or sciatica.

High-impact exercise can also cause dizziness, ringing in the ear, motion sickness, or loss of high-frequency hearing.

Some research further suggests that in people unused to exercise, intense activity increases production of harmful particles in the body called free radicals. These unstable oxygen particles injure muscle tissue. Muscle pain in this case does not occur until 24 to 48 hours after exercise.

Some people have a higher than average risk for injury:

About half of people at any age who participate in competitive running or high-impact aerobics experience minor injuries at least once a year. Young, intensely competitive athletes may be at risk for permanent injury. Studies are mixed over whether intensive high-impact sports in younger people cause long-term degenerative joint disease.
As more older people start exercising, there has also been a risk for injuries. Between 1990 and 1996, injuries from active sports increased by 54% in people age 65 and older.
Women are far more likely than men to suffer knee injuries.
Urinary incontinence affects many female athletes who engage in high-impact exercise.
Tennis players are at high risk for injuries from repetitive force on the shoulder joint.

Preventing High-Impact Injuries. The following may be helpful for preventing injury:

Wear shock-absorbing footwear with weight-dampening inserts.
Combine weight lifting with jumping exercises. This may prevent injury by strengthening hamstrings and improving coordination.
Vary training and alternate easy and harder workouts.
Be careful to warm up, cool down, and stretch. Flexibility is the key to preventing many muscle strains.
Take days off now and then. The risk of injury increases when athletes train more than five times a week.

Because of the association between high-impact exercises and oxidation, some experts suggest that eating foods rich in antioxidants, such as vitamins A, C, and E. Such foods include many fresh fruits and vegetables.

Treating Minor Injuries. Most mild or moderate injuries respond well to a simple, four-step treatment: rest, ice, compression, and elevation (RICE). This regimen works well for both spot injuries and chronic problems. Ice packs, which reduce inflammation and pain, can help acute injuries and can be useful for the first few hours after a chronically injured area is exercised. How much or how long to compress the injury is unclear. Evidence suggests that early movement is helpful, although taping or bracing in people with a recurrent ankle sprain is known to be protective. It may not be helpful in those without a previous ankle injury.

Minor injuries like sprains may be treated at home if broken bones are not suspected. The acronym RICE can help you remember how to treat minor injuries: "R" stands for rest, "I" is for ice, "C" is for compression, and "E" is for elevation. Pain and swelling should decrease within 48 hours. Gentle movement may help, but pressure should not be put on a sprained joint until pain is completely gone. This can take up to a few weeks.

Heat, ultrasound, whirlpool, and massage may speed healing if applied a day or two after the initial injury or for warm-up before another workout session.

Female Athlete Triad

Some young female athletes who exercise very intensely and are subject to intense pressure to remain thin are at risk for the so-called female athlete triad. This triad of symptoms includes menstrual dysfunction, eating disorders, and osteoporosis. Eating disorders among young female athletes is estimated at 15 - 62%. Women at higher risk include ballet dangers, gymnasts, and divers. Continued intense exercise causes a stress response in which estrogen (the primary female hormone) declines. Estrogen loss then can lead to infertility and osteoporosis. Iron depletion and anemia may also be a problem in women who exercise frequently, even at moderate intensity. A doctor should be consulted for any of these concerns.

Improper Mechanics and Its Effect on the Back and Shoulders

Incorrect movements can literally cause mechanical problems in the muscles. They are usually the result of improper exercise instruction and inattention. A single jerky golf swing or incorrect use of exercise equipment (especially free weights, nautilus, and rowing machines) can cause serious back injuries.

Between 30 - 70% of cyclists experience low back pain. Pain may be improved by adjusting the angle of the bicycle seat.

Dehydration

Everyone should drink lots of fluid during intense exercise. Thirst is often a poor indicator of dehydration in people who exercise, particularly older people. During a tough workout in a hot environment, the body can lose two liters of fluid per hour through sweat. Anyone who exercises intensively should take the following precautions:

Drink 6 to 8 ounces of fluid about 15 minutes before a workout, and then pause regularly during exercise for more.
Water is the best choice for replenishing body fluids. Glucose-sodium-potassium solutions, the so-called "sports drinks," that promise instant energy are apparently no better than water at improving endurance during prolonged intense running.
Caffeinated beverages like coffee and soft drinks give short bursts of energy but can actually reduce fluid. Caffeine before a workout has been shown to temporarily raises blood pressure and reduces blood flow to inactive limbs.

Contrary to popular belief, drinking fluids will not cause cramps. Adequate hydration, in fact, helps prevent the painful involuntary muscle spasms that sometimes occur during exercise.

Hyperthermia (Overheating)

Overheating, or hyperthermia, can be a problem with strenuous exercise or when working out in hot weather. Overheating can cause mild to life-threatening conditions. Heat exhaustion, a moderate form of hyperthermia, is characterized by the following symptoms:

Lightheadedness, nausea, headache, hyperventilation, fatigue, and loss of concentration.
A high temperature (above 103° F), possibly accompanied by complaints of chills and clammy skin.

Individuals should rest in a cool, dry place, drink plenty of fluids, and bring down their body temperature with ice packs pressed against the skin.

Heatstroke. Heatstroke is the most dangerous complication of hyperthermia. The victim may suddenly cease sweating, after which symptoms such as altered consciousness, seizures, and even coma, may quickly follow. Heat stroke is a medical emergency and requires immediate cooling of the victim in an ice-water bath or with ice packs. One study suggests that risk for serious complications from exercising in high temperatures may persist as late as the following day, even if the weather has cooled down.

Click the icon to see an image of the dangers of heatstroke.

Frostbite and Hypothermia

Precautions also need to be taken in cold weather. When exercising in winter, dress in layers, including gloves and socks, which create insulated air pockets that trap heat. In cold weather, wear shoes with less ventilation than those worn in the summer. Fingers, toes, ears, and nose are most susceptible to frostbite. From stinging or aching, frostbite progresses to numbness. Fingers and toes may become white. Soaking the extremities in warm water can help, but only once there is no risk of refreezing, since a second bout of frostbite after thawing can accelerate tissue damage. Hypothermia can be life threatening and can occur even after prolonged exposure to temperatures that are above freezing. The condition is characterized by extreme fatigue, mental confusion, apathy, and a lack of coordination. The victim should be warmed as soon as possible with blankets, body heat, and warm fluids.

Review Date: 3/6/2006
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital