The Effect of Physical Conditioning on Cardiac Response to Acute Exertion

Abstract

The effect of chronic exercise (training) and acute exertion on myocardial water and electrolyte metabolism, Na–K-ATPase activity, and morphology was studied in the male rat. Training increased the potassium content in myocardial cells, the effect depending on the duration of the training period. Potassium accumulation in the heart cells was not associated with the cardiac hypertrophy that developed relatively quickly and depended primarily on the intensity of work, rather than on the duration of the training period. The most regular effect of acute exertion on myocardial electrolyte content was potassium uptake by the heart. Chronic physical overload, depending on its severity, reduced or abolished the heart's ability to accumulate potassium during physical exertion. An attempt was made to evaluate the possible role of Na–K-ATPase in the mechanism of depression of potassium transport against its electrochemical gradient after chronic physical overload. In comparison with normal response of the heart, both morphological and biochemical changes were diminished in both the trained and, to a smaller extent, the overtrained heart during acute extreme exertion. It is concluded that potassium accumulation in myocardial cells is an essential adaptive reaction to physical exertion and the extent of potassium uptake depends on the functional state of the heart.