Sustainability and perceptual responses during handgrip holds to failure at two fatigue thresholds

Purpose: Critical force (CF) provides an estimate of the asymptote of the force-duration curve and the physical working capacity at the rating of perceived exertion (PWC_RPE) estimates the highest force that can be sustained without an increase in perceived exertion. Handgrip-related musculoskeletal disorders and injuries derived from sustained or repetitive motion-induced muscle fatigue are prevalent in the industrial workforce. Thus, it is important to understand the physiological mechanisms underlying performance during handgrip specific tasks to describe individual work capacities. This study examined prolonged, isometric, handgrip exercises by comparing the relative force levels, sustainability, and perceptual responses at two fatigue thresholds, CF and PWC_RPE. Methods: Ten women (26.5 ± 3.5 years) performed submaximal, isometric handgrip holds to failure (HTF) with the dominant hand at four, randomly ordered percentages (30, 40, 50, and 60%) of maximal voluntary isometric contraction (MVIC) force to determine CF and PWC_RPE. Isometric handgrip HTF were performed at CF and PWC_RPE. Time to task failure and RPE responses were recorded. Results: There were no differences in the relative forces (p = 0.381) or sustainability (p = 0.390) between CF (18.9 ± 2.5% MVIC; 10.1 ± 2.7 min) and PWC_RPE (19.5 ± 7.9% MVIC; 11.6 ± 8.4 min), and the RPE increased throughout both holds at CF and PWC_RPE. Conclusion: It is possible that complex physio–psychological factors may have contributed to the fatigue-induced task failure. CF and PWC_RPE may overestimate the highest force output that can be maintained for an extended period of time without fatigue or perceptions of fatigue for isometric handgrip holds.