How running helps your muscles, which helps your running

By Trevor Smith
AmericanRunning.org
8/20/2003

An amazing feature of your muscles is how much you can change them by training. When you begin an aerobic training program, the capillary blood vessels in the muscles you use begin to increase. You can end up with almost another 50%, added to the capillary network you had before you began training.

Your muscles need enzymes to tell the power houses (called mitochondria) in their cells how to carry out the biochemical reactions that turn carbohydrate and fat into energy. The enzyme activity can more than double with consistent training.

Part of the fuel your muscles use is right there in the muscle fibers. This is a complex carbohydrate called glycogen. As you train, your muscles' capacity for glycogen increases, so you can boost your stored glycogen by eating more carbohydrates.

If you carbo-load by increasing your carbohydrate calories to at least 70% of your total calories for at least three days, you may be able to increase your muscles' glycogen store by more than 50%.

If you practice speedwork, or any high-intensity efforts that put you into oxygen debt, your muscles produce more lactate as a byproduct. This causes blood lactate to rise. The increase is gentle at first, and then rises more sharply. This steeper increase in blood lactate is called the lactate threshold.

Regular speedwork in your sport will raise your lactate threshold. This means that your muscles can work harder to produce only the same amount of lactate. This allows you to run (or ride, or ski, or row ...) faster.

One of the most dramatic changes in sedentary people as they grow older is their muscles grow smaller, accumulate more fat, and become weaker. You can avoid the major part of these changes by resistance training. Build up to eight to 12 repetitions of the heaviest load you can handle, for each of your major muscle groups.

Two or three sessions a week are enough; you even gain some benefits by working out only once a week, according to Michael Pollock, Ph.D., and colleagues at the University of Florida in Gainesville.

Working out against high resistance (or lifting heavy weights) causes microscopic damage in muscle fibers. During the recovery period before the next workout, the fibers grow bigger and stronger.

And it's never too late to benefit. Even frail folks in their 90s increased muscle size by up to 10%, and strength as much as doubled, according to Maria Fiatarone, M.D., and colleagues at Tufts University in Boston.

Regular aerobic training and strength workouts, proper diet and plenty of fluids will keep your athlete's muscles young, no matter what the calendar says about your age.

Copyright, The American Running Association.