Your center of gravity is the spot in your body with equal weight in front and in back. Every motion you make is aimed at keeping your body balanced around your center of gravity. When you run and move one part of your body forward, you must move another backward to keep you from falling on your face. When you move your left leg forward, you must also move your right arm forward and your left arm backward.
People with poor running form often look funny because when they move their right leg forward, they don't move their left arm forward fast enough. It is usually of little value for a coach to tell an awkward student to change his form. The person should first be evaluated by a physician for conditions that affect nerves and muscles. If none is found, the coach should have the student repeat the motion over and over until the brain can coordinate the body's motions about his center of gravity. With repetition and increased speed, the body will move more smoothly. If you want to improve your running form, run every day and when you are in good shape, run short interval sprints as fast as you can. A typical twice-a-week workout would be to run 15 100-yard sprints with a short rest between each.
Q: What's the current advice on exercise during pregnancy?
A study from the Columbia University School of Public Health found that women who exercised regularly had larger babies (Journal of Obstetrics and Gynecology, Sept. 1993). This is an exciting finding because larger babies tend to be healthier. We used to think that heavy exercise would decrease blood flow to the unborn baby and interfere with its growth. Another concern was that high body temperature during the first month of pregnancy could cause brain and spinal cord damage, but the belief was based on pregnant women whose high fevers were caused by infections. A woman's body temperature can rise above 101 degrees after 10 minutes of fast running on a warm day. It takes at least 12 minutes for body temperature to rise above 101 degrees in a hot tub. A study from the University of Vermont showed that pregnancy, by itself, helps to keep a woman's body temperature from rising too high. At the same level of intensity, a woman's body temperature was significantly lower during pregnancy than before pregnancy.
Pregnant women should check with their doctors, but the vast majority can exercise. The only concern is that a forward-leaning pregnant uterus can cause back pain if you run during the last three months of pregnancy. Extreme sports that may involve banging the belly, such as sky diving or kick boxing, should certainly be avoided.
Q: I know I'm supposed to exercise while I'm trying to lose weight, but it doesn't seem to help much. What am I doing wrong?
A: To use exercise to help you lose a lot of weight, you have to exercise intensely. The amount of fat in your body correlates more with how hard you exercise than with how much you exercise. When you lie down in bed at night, you burn around 60 calories an hour. On the night after you exercise vigorously, you burn around 70 calories per hour. When you exercise vigorously, your body temperature rises, and it can remain elevated for up to 18 hours. When you exercise at a leisurely pace that does not raise your temperature, your metabolism does not increase.
For exercise to help you lose weight and keep it off, start an exercise program in which you move continuously, such as dancing, cycling, skating, walking or jogging. Start at a leisurely pace and stop immediately when your muscles feel heavy or hurt. Gradually, you should be able to work up to the point where you can exercise continuously for 10 to 30 minutes a day. Then you can start working more intensely. On one day, start slowly and gradually increase the pace until your muscles start to feel heavy or hurt, and then slow down. When you recover, pick up the pace again. Do this until your muscles stop recovering. If your legs feel heavy on the next day, don't exercise. If they feel fresh, exercise at a very leisurely pace. Alternate these workouts and you will lose more weight because you will burn more calories while you sleep.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.