THE SCALING OF EFFORT PRODUCED BY STRENOUS ISOMETRIC MUSCLE CONTRACTIONS.

Thirty-five Ss were required to maintain manual loads equal to 30, 40, 50, 60, 70, and 80 of their maximum strength as long as possible and to report the intensity of the effort required by the task on a five-point scale. With each increase in load, endurance was reduced and effort developed at an increased rate, showing that effort rating was sensitive to variations in contraction strength. External occlusion of the blood supply to the contracting muscles, especially at the lighter loads, also produced briefer maximum contraction times and accelerated the reports of the various levels of effort. The contraction strength at which the internal pressure in the muscle effectively occluded the blood supply was found to be between 60 and 70 of maximum strength. The data were transformed to eliminate differences in endurance produced by the various experimental conditions by expressing the time of appearance of each level of effort as a percentage of the time at which maximum effort was reported for that condition. When this was done, it was found that effort was a linear function of the percentage maximum contraction time. Author