Question: When I exercise in the morning, my legs sometimes feel really tired after about 15 to 20 minutes. What causes this and do you have any suggestions to avoid it? I have occasional asthma, but usually not when this happens.

Dr. Hibberd's Answer:

There are too few details to be specific with a more targeted answer, but I'll give you a few pointers:

1) Adequate hydration with water or various commercial replacement solutions (no real advantage except they are expensive and look good!) is very important for all athletes, both before, during, and after exercise.

2) Avoid eating within two hours of exercise.

3) Cramps, discomfort, or fatigue that are recurring and are induced by exercise should be evaluated by a physician. Cramps that relate to exercise and are relieved rapidly by rest may reflect inadequate blood supply, and you may benefit from an arterial insufficiency evaluation.

4) Never attempt exercise when your asthma is not well controlled. Bronchial airways are often blocked by approximately 70 percent or more before audible wheezing is evident, and you may not have sufficient reserve to safely exercise. Many asthmatics take pre-exercise medications to protect them from exercise-induced flares of their asthma. DO NOT EXERCISE WHEN WHEEZING.

5) Avoid exercising in heated areas or in temperatures over 100 degrees without periodic fluid breaks and perhaps some gear that will protect you from overexposure and heat exhaustion. We now have heat alert monitors available for inclusion in sporting equipment to alert you to heat exhaustion, especially if you are exercising outside in the direct sun or the heat of summer.

6) Oxygen supplementation is not advised to increase endurance. Just as other ways of boosting endurance are discouraged in amateur and professional athletics, these supplemental treatments may even permanently disqualify you from competition.