The influence of body fat on isometric exercise performance

Abstract

The effect of body fat on the ability to sustain a fatiguing isometric contraction and on the recovery of strength and endurance following these contractions was examined here. Five overweight (average body fat = 28.6%) and five normal weight (average body fat= 11.4%) subjects were asked to perform pairs of isometric contractions of their handgrip muscles sustained to fatigue at tensions of 25,40,70 and 90% of their maximum strength (MVC). The interval between the contractions was set at 3,7,12,20 and 60 min. In an additional series of experiments, these same subjects were asked to exert an MVC at 3,7,12, and 20 min following an isometric contraction at either 25, 40, 70 or 90% MVC. It was found that although the overweight group had more strength than the normal weight group, their endurance was less for sustained isometric contractions at any tension examined here. In contrast, endurance initially recovered more rapidly in the overweight than the normal weight group but the time required for both strength and endurance to recover fully was the same in both groups.

Perceived force in fatiguing isometric contractions

“…This meter served as a monitor for the subject in maintaining reference forces. In previous studies, it has been shown that there is an inverse relation between the force of muscular contraction and isometric endurance (Devries, 1968;Petrofsky & Phillips, 1981) and between strength and endurance (Petrofsky, Burse, & Lind, 1975). Our results confirm these findings.…”

“…It has been shown that there is a variable rate of recovery in the ability of muscles to sustain exertions following constant force contractions maintained until exhaustion. The recovery is fastest at higher forces and slowest at lower forces (Funderburk et al, 1974;Petrofsky & Phillips, 1981), and is assumed to depend on the rate of removal of waste products, some of which accumulate in higher concentrations during low force (30% MVC) contractions (Karlsson, Funderburk, Essen, & Lind, 1975).…”

Muscle recovery from a short fatigue test and consequence on the reliability of EMG indices of fatigue

“…Studies in which repeated back muscle fatiguing contractions were performed and where a complete recovery between the tests was assumed used varying rest intervals ranging between 10 and 15 min without justification (Kondraske et al 1987;Roy et al 1989). These rest intervals appear to be in agreement with previous results obtained with handgrip fatiguing contractions (Funderburk et al 1974;Petrofsky 1981;Petrofsky and Phillips 1981). However, the effect of rest intervals has never been tested on back muscles.…”

“…In fact, the restitution of mechanical variables (force, endurance time) necessitates a longer rest bout (Funderburk et al 1974;Kroon and Naeije 1991;Petrofsky 1981) than MF. Results on handgrip contractions (60-70% MVC until exhaustion) reveal a complete recovery of strength after 10-12 min (Funderburk et al 1974;Petrofsky 1981;Petrofsky and Phillips 1981). Moreover, there is a corresponding recovery of endurance levels of 80-90% after 10-12 min rest Fig.…”

“…In fact, considering that the Rohmert's prediction equation was developed for limb muscles, 10 min recovery appears a conservative estimate because back muscles are generally less fatigable than limb muscles (Jorgensen 1970;Jorgensen et al 1993). However, the Rohmert equation is based on the recovery of muscle force rather than recovery of muscle endurance, which takes longer to recover (Funderburk et al 1974;Petrofsky and Phillips 1981). This latter element necessitates a closer look at the results.…”