2000 Volume 45 Issue 6 Pages 695-706
In previous studies, many parameters to evaluate static muscle endurane have been proposed, but their properties and relationships have not been sufficiently examined. In sustained maximal static exertion, muscle exertion can be classified as a remarkable phase and a nearly steady state phase of strength decrease. Both phases could relate to different physiological factors of muscle endurance, but little is known about evaluation parameters for either phase. This study aimed to examine the properties and relationships of various evaluation parameters, including the transition time when the decrease in speed shows a distinct change, by analyzing the force-time curve of sustained static hand gripping(SSHG), and to propose effective parameters. Thirty healthy university students were selected as subjects. SSHG work demanded an exertion of maximal muscle strength(MAX) for 12 minutes. Evalution parameters were calculated for 6 and 12 minutes. The time(t5), when the determination coefficients of two regressions based on a remarkable phase and a steady state phase of strength decrease became maximal, was considered effective to statistically evaluate a change point of decreasing rate. It was also suggested that the time(t1), when the exertion value is furthest from the linear line between MAX and the last exertion value, and the time(t4) of the intersection of the regression(y_1=a_1X+b_1) based on exertion values until t1 and the regression(y_3=a_3X+b_3, a_3=0) based on exertion at a steady state, were effective because the change with different measurements of 6- and 12-minites was less. Moreover, muscle oxygenation during SSHG decreased from the beginning of SSHG to 40-60 seconds. It was considered that obstruction of the blood flow caused an insufficient oxygen supply. This time period was almost consistent with change times(t1, t4, t5) of exertion value. It was suggested that parameters such as the regression coefficient(a1), the persisting times of 80%, 70%, and 60% of MAX and the sum of the decrement of exertion for the first 1 min can evaluate a remarkable phase of strength decrease. Total integrated area, the last strength exertion value and decreasing rate are appropriate for a nearly state phase. Further, it was considered that all parameters except the transition time(t1-t4) and regression coefficient(a2) can be evaluated almost equally at 6 minutes instead of 12 minutes.