Comparison Of Force Responses During Continuous Handgrip Holds Anchored To Low And High Perceptual Intensities

The rating of perceived exertion (RPE)-Clamp Model has been used to examine the interaction between fatigue-induced changes in force when exercise is anchored to a fixed RPE. Critical force (CF) reflects the highest force that can be maintained for a very long time without fatigue. PURPOSE: This study investigated the time course of changes in force, relative to CF, during sustained, isometric, handgrip holds to failure (HTF) anchored at a low and a high perceptual intensity. METHODS: Twelve men (28.2 ± 3.8 yr) performed handgrip HTF at 4 different submaximal intensities (% maximum voluntary isometric contraction [MVIC]) to determine CF, followed by HTF anchored to RPE 3 and 7 on the 10-point omnibus resistance scale. CF was the slope coefficient of the total work for the 4 holds plotted as a function of time to task failure (TTF). A 2(RPE: 3 vs 7) x 21 (time: 0%-100% TTF) repeated measures ANOVA with appropriate follow-up and post-hoc analyses were used to compare forces each time point (5% to 100% TTF), relative to 0% TTF, and between RPE 3 and 7 at each timepoint. RESULTS: A paired samples t-test indicated there was no difference (p = 0.73) in TTF between RPE 3 (479 ± 197 s) and 7 (496 ± 174 s). Overall, there were decreases in force, relative to 0% TTF (RPE 3: 21 ± 4% MVIC; RPE 7: 37 ± 5%MVIC), from 20% to 100% TTF for RPE 3, and from 10% to 100% TTF for RPE 7 (p < 0.01). The patterns of force responses were described by an early, mid, and end phase. In the early phase, the forces for RPE 7 were greater than RPE 3 and there were significant decreases in forces below CF (19 ± 4% MVIC) across time for both RPE holds. The times to CF at RPE 3 and 7 were 19 s and 65 s, respectively. In the mid- phase, the forces reached a relative plateau around 7-10% MVIC, and the forces at RPE 3 and 7 intermittently converged (not significantly different). In the end phase, the forces at both RPEs converged and finally reached task failure (0 N). CONCLUSIONS: The CF did not demarcate a fatiguing from non-fatiguing force as force continued to decrease beyond CF. The subjects’ initial force selection may be explained by a feedforward mechanism, while a combination of corollary discharges and afferent feedback (i.e., sensory tolerance limit) may explain the continuous decreases in force, and ultimately task failure by reducing the central motor drive to maintain the prescribed RPEs.