Cardiovascular responses to static exercise. (Isometrics, anyone?).

ANYONE with a stethoscope, a sphyg-momanometer, and an open mind can readily satisfy himself that static effort or "isometrics" may raise the blood pressure to high levels. Yet, isometrics, as a form of exercise intended as a means of attaining physical fitness, has been urged on the population at large. A recognition of the fact that the obese, the infirm, and the aged are unlikely to commence jogging around the neighborhood before breakfast, apparently has recently led some advocates of isometrics (including physicians) to write in the open press urging the waddlers to turn instead to press-ups (push-ups) and pull-ups. Judging by current advertisements, the sale of a variety of devices for isometric exercises may have become brisk. In view of these trends, it is worth while to reiterate certain reported data concerning the physiologic responses to isometric exercise and to examine the case for and against this type of activity. There are many kinds and degrees of static effort. Common examples are lifting, holding or carrying objects of all kinds, pushing furniture, and opening doors or windows that are difficult to move. Everyone is familiar with the tiring effects of holding or carrying large, awkwardly shaped objects. Working with the arms overhead is another common example since a good deal of static effort is needed to hold the arms in position, even before muscular activity or the weight of tools has been added. Isometric training has been shown to improve the strength of a muscle group. To attain this improvement, the training stints must be undertaken at tensions of 50% or more of the muscle's maximal capacity. While the increase in efficiency of any physiologic function is a worthwhile goal, the only known improvement as a result of such training is in isometric strength. With isometric training there is strikingly little associated increase in aerobic capacity or cardiovascular efficiency and little contribution to fitness for sustained dynamic exercise.' There is clear evidence that any muscle group can maintain tensions of up to 10% or 15% of the maximal capacity (MVC) for a long time. At these low tensions, the heart rate and blood pressure increase by a few beats per minute and by some 5 to 15 mm Hg, respectively, to reach a steady state which continues for as long as the tension is maintained. The muscle blood flow also increases to a steady state, which clearly sets the …