Running faster means changing muscle fibers


November 17, 1992|By Dr. Gabe Mirkin HTC | Dr. Gabe Mirkin HTC,Contributing Writer

World records in running are improving at a fantastic rate, and recent studies indicate those records are getting faster because runners are running much faster while they train.

Thirty years ago, top marathon runners trained by using an interval workout of 40 quarter-mile runs averaging about 67 seconds each. Today, no knowledgeable marathon runner would run that many quarter-mile repetitions at such a slow pace. A more respectable workout would be to run only 12 quarters, but to make each run much faster, averaging less than 60 seconds each.

Research led by Dr. Ben Londeree of the University of Missouri explains why running fewer intervals at a faster pace helps runners to travel faster when they race.

Muscles are made up of two types of fibers: white strength-and-speed fibers and red endurance fibers. The strength-and-speed fibers are further classified into slow-twitch type A fibers, which use oxygen efficiently, and fast-twitch type B fibers, which do not use oxygen efficiently.

During very fast endurance running, most of the lactic acid (the substance that causes muscle fatigue) that builds up in the muscles is produced by the fast-twitch type B fibers. That means fatigue during a race comes primarily from a lack of oxygen in those fibers.

Running so fast that you develop a severe oxygen debt converts fast-twitch type B fibers into the slow-twitch type A fibers, which do not put out as much lactic acid.

To run faster in races, you should train by running progressively faster in practice once or twice a week. That will improve the ratio of slow-twitch type A fibers in your muscles so that you can run faster in races without feeling tired.


Q: I've tried every diet scheme in the world, and I always gain back every pound I lose. What can I do to lose weight and keep it off?

A: More than 85 percent of women and 50 percent of men think they are too fat. Shrewd entrepreneurs take great advantage of that fact by creating a host of plans and products that are supposed to help us lose weight. But there is no substitute for a program of proper diet and regular exercise to achieve and maintain a healthy weight.

It is far safer to remain obese than to repeatedly lose weight and gain it back again.

Simply restricting calories will not help you lose weight permanently. Most people refuse to eat so little that they have to go to bed hungry. And packaged diet foods aren't any bargain. You might limit your diet to low-calorie drinks or low-calorie pre-packaged meals for a short time, but you won't be able to limit your food intake to these meals forever.

Pills to suppress your appetite won't work either. They become ineffective as you continue to take them. Most will raise your blood pressure and make you feel jumpy.

To lose weight permanently, you have to adapt to a lifestyle you can follow forever. You need to severely reduce your intake of fat, and you need to start an exercise program.

Q: I'm intrigued by TV ads for juice machines. Are juices really that healthy?

A: You cannot improve the quality of a food product just by extracting something from that food. Protein supplement pills, for example, are no more healthful than the milk or tuna used to make them. The same applies to juices.

Juices may actually be less healthful than the fruits and vegetables used to make them. Juicing removes most of the fiber from the fruit or vegetable. Orange juice, for example, contains only 1 percent as much fiber as an orange does. You need fiber to help lower cholesterol, reduce weight, and to prevent constipation, gall bladder disease and colon cancer.

Besides, you can't live on juice alone. You need protein, and fruits and vegetables contain very little of that nutrient.

Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.

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