Time to fatigue during isometric exercise using different muscle masses.

The purpose of this study was to test the hypothesis that differences in the pressor response to static exercise using varying muscle masses are due to differences in endurance time. i.e., time to fatigue. Ten healthy, male subjects (mean age 24 +/- 3 years) participated in the study. With no knowledge of the purpose of the study, the subjects were instructed to maintain static contractions for as long as possible during 30% maximal voluntary contraction (MVC) in handgrip (HG), two-leg extension (LE), and dead lifting (DL). Inability to sustain a contraction within 10% of the designated force (30% MVC) marked the endurance time end point. During sustained contractions, heart rate, blood pressure, and time to fatigue were measured. Times to fatigue were 3.39 +/- 0.92, 3.61 +/- 1.67, and 3.68 +/- 1.34 min for HG, LE, and DL, respectively. These differences were not significant (p greater than 0.05). Heart rate and blood pressure increased progressively with sustained contractions, DL greater than LE greater than HG. LE and DL responses were consistently and significantly (P less than 0.05) higher than HG responses reflecting the magnitude of absolute force of contractions. The magnitude of the pressor response to the three sustained static contraction maneuvers was not related to the time to fatigue. The data affirm the view that the pressor response is a function of muscle mass activated and the absolute force developed during static exercise.