Contralateral Thermal Pain and Naturally Occurring Muscle Pain Have Different Effects on Force Production During a Fixed Perceived Effort Handgrip Task

Abstract

Background In the presence of pain, performance during imposed workload motor tasks may be maintained at the cost of a higher perceived effort. This study investigated how experimentally induced contralateral thermal pain and naturally occurring muscle pain influence force production during a fixed perceived effort task. Methods Forty young adults performed intermittent isometric handgrip contractions at light (13/100) or hard (50/100) perceived effort intensities across two visits. Each visit included an experimental condition, featuring contralateral thermal pain in Block 1, and a control condition, with non-painful warm stimulation in Block 2. Participants completed 10 blocks (five repetitions of Block 1 and Block 2), with force production and electromyography continuously recorded. Participants rated thermal and muscle pain after each block. Results Force production was higher during thermal pain compared to control, with no interaction with perceived effort intensity. Regression analysis showed that each one-unit increase in muscle pain (0–100 scale) corresponded to a reduction in peak force (0.45 N), mean force (0.32 N) and force integral (1.02 N·s). Conclusions During a fixed perceived effort task, contralateral thermal pain increases force production. In contrast, muscle pain is associated with reduced force production. This study suggests that the type of pain has a varied effect on force production during voluntary motor tasks. This study questions the well-accepted inhibitory effect of pain on force production and encourages future research to use fixed perceived effort tasks to fully appraise the effects of different pain types on force production. Significance Statement This study shows that pain-related changes in force production during self-regulated exercise are pain-type dependent. Using a novel fixed perceived-effort paradigm, we found that contralateral thermal pain increased force production, whereas naturally occurring muscle pain reduced force output. These findings extend knowledge derived from fixed-workload tasks and suggest that distinguishing pain types may improve understanding of motor regulation in exercise, rehabilitation, and clinical contexts.