What's Going On in There?

Continued...

In trained athletes, the cardiac output can increase up to eight times the resting output. This is brought about not only by an increase in heart rate, but also by a training-induced increase in the stroke volume - the amount of blood ejected with each heartbeat.

Also, in trained athletes the stroke volume can increase up to 50 to 60 percent during exercise. This is due to an increased force of contraction and a greater emptying of the heart chamber. At rest, the aerobically trained woman will have a slower heart rate and increased stroke volume.

In addition, the heart of an aerobically trained person often increases moderately in size, primarily by an enlargement of one of its four chambers, the left ventricle, which pumps blood away from the heart to the working muscles.

If you train primarily by weight lifting or strength training, your heart adapts in a different way. Your heart must generate more force with each beat to eject blood against the increased pressure in the blood vessels caused by isometric or static muscle contraction. As the heart works under increased pressure from nearby blood vessels, it responds to this pressure by increasing the thickness of its left ventricular wall.

The heart muscle thickens without enlargement of the internal chambers. The thicker muscle generates more force with each beat to eject blood against resistance. This adaptation allows weight lifters to meet the demands of their training. if you train both aerobically and with weight lifting, your heart will adapt in proportion to each type of training.

Changes in the heart muscle occur gradually over the first four to eight weeks of consistent training. Whether you train aerobically or lift weights, your workout will get easier. Aerobic exercisers also will notice a decrease in resting heart rate.

There are also adaptations to the circulatory system, including one that make may you appear anemic when you are not.

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Foreword: Billie Jean King

Comments by Barb Harris
Editor in Chief,
Shape Magazine

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