What's Going On in There?

Continued...

Muscular Adaptions

Training also causes major changes in your muscles. During exercise, muscle oxygen consumption increases up to 70 times above resting values. More than 4,000 capillaries may be delivering blood to each square millimeter of muscle cross-section.

As you exercise, capillary density increases up to 40 percent, enabling more oxygen, nutrients and hormones to be delivered to the muscles, and stimulating better removal of heat. Aerobic training also increases the muscles' ability to use oxygen to produce work and improves their ability to store glycogen, combined glucose molecules that provide energy.

Strength training increases muscle size and strength. Both types of exercise develop more mitochondria, the subcellular powerhouses that use oxygen to convert glycogen to usable energy known as ATP (adenosine triphosphate). With more mitrochondria, you can produce more energy.

The kind of training you do affects the changes in your muscle fibers. Muscle fibers come in two types: fast-twitch for sprint-type activity and slow-twitch for endurance activity. Each of us is genetically endowed with our own particular proportion of these, though most people have about 50/50.

Training does not significantly increase or change the fiber type, but it does maximize the abilities of the particular fiber type. Training for speed and power develops the fast-twitch fibers, while training for endurance develops the slow-twitch fibers.

Resistance training induces the muscle to develop greater contraction force and can increase individual muscle-fiber size by 45 to 50 percent. It also increases the amount and strength of connective tissue around the muscle cells, improving the functional support and strength of adjacent tendons and ligaments. In turn, this provides some protection from joint and muscle injury.

Most of the increase in muscle size from training is the result of an increase in the size of the muscle fibers, not an increase in their number. Men develop bigger muscles than women because they have more testosterone, the hormone that affects the development of muscle size.

The amount of muscle enlargement you naturally develop with training is in part determined by your testosterone level, and by the amount and type of muscular work you do. The visibility of your muscles is affected by their size and the amount of overlying fat. If you're leaner, your muscles will be more visible.

When you design your training program to achieve the results you desire, be sure to consider both your genetic endowment and your training techniques. And be patient with your body. Everybody responds at a different rate and according to her potential.

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About the authors: Carol L. Otis, M.D., is Chief Medical Advisor to the Sanex WTA and UCLA student health physician. Roger Goldingay is a former professional soccer player. They are married and the co-authors of The Athletic Woman's Survival Guide.

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Table of Contents

Foreword: Billie Jean King

Comments by Barb Harris
Editor in Chief,
Shape Magazine

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