Isometric strength, endurance, and the blood pressure and heart rate responses during isometric exercise in healthy men and women, with special reference to age and body fat content.

The relationship of sex, age, and body fat content were assessed on the maximal voluntary strength (MVC), the endurance of a sustained contraction held at 40% of the subject's maximal strength, and the associated changes in blood pressure and heart rate. Isometric hand-grip strength was, as expected, greater in men than in women; however, in both sexes, age was inversely related to isometric strength, particularly in women. Body fat content, however, was directly related to strength. In contrast, in both male and female subjects aging was directly related to isometric endurance while body fat content was now inversely related to isometric endurance. The increase in heart rate throughout a fatiguing contraction at 40% MVC was strikingly similar in men and women. Heart rate, which always increased during exercise, attained its highest magnitude during exercise in the subjects who had the highest resting heart rates. However, older subjects displayed a smaller increase in exercising heart rates than younger subjects. The blood pressure at the end of the 40% MVC was directly related to the resting blood pressure. However, aging and body fat content both increased the resting systolic blood pressure in men and women; this aging effect was further exaggerated during the exercise.