When a pregnant woman asks for advice about exercise, she may not be satisfied with a reply of "go easy." Although much remains to be learned about the effects of exercise during pregnancy, enough information is available to offer some safety guidelines as follows:

• Reduce weight bearing exercises (e.g. running) in favor of non-weight bearing exercises (e.g. swimming, bicycling). This is tolerated more easily, especially as maternal weight increases. Also, in view of the joint relaxation that occurs during pregnancy, dislocations are less likely with non-weight bearing exercise.
• Avoid impact exercise. Stresses inherent in running, jumping, and intense stretching can lead to disclocation more readily in a pregnant woman. Stresses to the lower back should also be avoided.
• Exercise for shorter periods and rest frequently. A woman can minimize the problem of fetal hyperthermia by allowing adequate time for heat dissipation. One sensible approach is to alternate 15-minute exercise intervals with rest periods lasting 3 to 5 minutes.
• Limit exercise intensity to levels no greater than pre-pregnancy levels.
• Avoid anaerobic exercise. Avoiding maximal exercise will prevent the build up of lactate and the acidosis that accompanies exhaustive exercise. A rule of thumb for reasonable levels of aerobic exercise is that a person should be able to carry on a conversation while exercising.
• Avoid heart rates above 140 beats per minute. Exception: If the patient was already exercising at training levels (70 percent of age predicted maximum heart rate) before her pregnancy, it may be safe for her to continue, even if this involves a heart rate higher than 140. In these instances, however, adequate rest every 15 minutes is mandatory.
• Discontinue exercise if vaginal bleeding or abdominal pain occurs. A woman should see her provider if these symptoms develop.
• Maintain a regular program of prenatal care. Patients should keep their provider informed about the type and amount of exercise performed. Fetal well-being, adequate maternal weight gain, and maternal well-being should be documented.
• Walking and swimming are the best exercises during pregnancy. Women generally feel better if they remain active as long as their pregnancy allows.