Experimental thermal pain and naturally occurring muscle pain have different effects on force production during a fixed perceived effort handgrip task

In the presence of pain, performance during imposed workload motor tasks may be maintained at the cost of a higher perceived effort (PE). This study investigated how experimentally induced thermal pain and naturally occurring muscle pain influence force production during a fixed PE task. Forty young adults performed intermittent isometric handgrip contractions at light (13/100) or hard (50/100) PE intensities across two visits. Each visit included an experimental condition, featuring 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 muscle electromyography continuously recorded. Participants rated thermal and muscle pain after each block. Force production was higher during thermal pain compared to control, with no interaction with PE intensity. Regression analysis showed that each one-unit increase in muscle pain (0–100 scale) corresponded to a reduction in peak force (0.37N), mean force (0.25N), and force integral (0.80N·s). During a fixed perceived effort task, thermal pain prompts an increase in force production, possibly reflecting attentional mechanisms related to exercise-induced hypoalgesia. In contrast, muscle pain is associated with reduced force output, likely because more force would perpetuate more muscle pain. Therefore, 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 PE tasks to fully appraise the effects of different type of pain on force production.