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Heart Rhythm Strips Broken Heart
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Figure 84-8

Effects of muscle exercise on blood flow in the calf of a leg during strong rhythmical contraction. The blood flow was much less during contraction than between contractions. (Redrawn from Barcroft H, Dornhors AC: Blood flow through human calf during rhythmic exercise. J Physiol 109:402, 1949.)

and other nutrients to the exercising muscles. For this purpose, the muscle blood flow increases drastically during exercise. Figure 84-8 shows a recording of muscle blood flow in the calf of a person for a period of 6 minutes during moderately strong intermittent contractions. Note not only the great increase in flow— about 13-fold—but also the flow decrease during each muscle contraction. Two points can be made from this study: (1) The actual contractile process itself temporarily decreases muscle blood flow because the contracting skeletal muscle compresses the intramuscular blood vessels; therefore, strong tonic muscle contractions can cause rapid muscle fatigue because of lack of delivery of enough oxygen and other nutrients during the continuous contraction. (2) The blood flow to muscles during exercise increases markedly. The following comparison shows the maximal increase in blood flow that can occur in a well-trained athlete.

Resting blood flow

Blood flow during maximal exercise ml/100 g Muscle/min

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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