Do you think you would be able to run a marathon faster by running short distances very fast once or twice a week and doing fewer miles overall, or by running more than twice as many miles slowly?
Surprise. You'll do better if you train by running short distances very fast. Strengthening your leg muscles will help you to run longer, even in a marathon. The principle of specificity applies to strength training.
To become strong for running, you have to strengthen your leg muscles, using the same motion that you use while running. Therefore, the best strength training for running is to run short distances very fast once or twice a week. With faster running, you push against the ground with greater force and become stronger. However, every time that you run fast, your muscles are injured, so you should not try to run fast more often than every other day.
Lifting weights and pushing against strength training machines will also help you to run faster. A study in the Journal of Applied Physiology showed that strengthening the legs with weights does not increase a runner's ability to take in and use oxygen, but it does increase their time to exhaustion by 13 percent and help them to run faster in six-mile races. Having stronger muscles helps you to run faster over longer distances. If you are a competitive runner, try to run very fast one to three times a week, even if it reduces the number of miles that you can run. You may also benefit by strengthening your legs with weights.
Q: I've been a serious triathlete for six years, but lately I feel tired all the time and just can't get through my normal workouts. What can I do?
A: Competitive athletes frequently reach a point in their training when they feel tired and can't get through their workouts. There are lots of theories to explain this phenomenon, and most are wrong.
Athletes used to be told that tiredness was caused by low mineral levels and were advised to eat lots of fruit for potassium and nuts for magnesium and to take salt tablets for sodium.
However, researchers have repeatedly shown that healthy athletes rarely suffer from deficiencies of potassium, magnesium, sodium or calcium. Viruses and other infectious agents will certainly cause athletes to feel fatigued. However, most of the time, doctors can't find them.
The most common cause of chronic fatigue in competitive athletes is muscle damage. You train for competition by taking a very hard workout on one day, which tears your muscle fibers to shreds and makes your muscles feel sore on the next day. Then you're supposed to take easy workouts until the soreness disappears.
However, many athletes are so obsessed with training that they attempt another hard workout before their muscles have recovered. This prevents muscle fibers from adequately storing muscle sugar for fuel, so they contract with less force and tire earlier.
Then the athlete keeps on pushing and tears the muscle completely, so he has to take a rest.
If you find that you can't get through your workouts, the odds are overwhelming that you are training too much. Take a rest, and if you do not recover in a few days, ask a doctor to look for a hidden infection or other cause.
I've stopped eating butter, but I'm not sure which kind of margarine is best. What do you recommend?
Eating too much fat makes you fat and raises your cholesterol. Margarine is the leading source of fat in the American diet. Some people still think that eating extra margarine helps to prevent heart attacks. I think the best kind of margarine is no margarine at all.
Because eating large amounts of animal fats is associated with heart attacks and certain cancers, many Americans felt that they could prevent heart attacks by using bakery and snack products made with vegetable oil and substituting margarine for butter.
However, the unsaturated fats in vegetable oils have a relatively short shelf life, so manufacturers found that they could make the products last longer by converting the unsaturated fats in vegetable oils into partially hydrogenated trans fats.
The partially hydrogenated fats that were placed in foods to substitute for saturated animal fats now appear to cause heart attacks and cancers as much or more than saturated fats.
Drs. Walter Willett and Albert Ascherio of Harvard Medical School feel that at least 30,000 extra deaths due to heart attacks may come from eating these partially hydrogenated trans fats. Indeed, another study from Harvard shows that heart-attack sufferers take in significantly more margarine and other sources of trans fats.
Partially hydrogenated fats raise blood levels of the bad LDL cholesterol and lower levels of the good HDL cholesterol. The Harvard doctors recommend a phaseout or strict limitation of partially hydrogenated fats in Americans' diets.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.