Background & Aims

Generally, pain invokes net inhibitive effects on motor command transmission (Chowdhury et al., 2022) and increases resource demand (Vogel et al., 2020). Thus, pain is expected to increase the perception of effort at a set task intensity (Norbury et al., 2022a) or reduce the perceived value to invest effort for continued task engagement (Richter et al., 2016). This relationship is evident during motor tasks where pain can originate naturally from the working musculature or externally via experimental pain methods like thermal stimulations. However, the potential differences or interactive effects between pain types on perceived effort and motor task behaviour is relatively unknown. Therefore, this study investigated the changes in motor output (force) during a fixed perceived effort task with concurrent acute muscle pain onset and external thermal pain application. We hypothesised that both sources of pain would lead to a reduction in force during fixed perceived effort tasks.

Methods

Forty healthy participants (50% female) aged 18–40 years were recruited. Across three visits, participants completed a familiarisation, then either a light (13/100) or hard (50/100) fixed perceived effort, intermittent isometric handgrip contraction task (3s ON-3s OFF). The task involved two blocks of ten trials with each trial involving five contractions. Trials and blocks were separated by 15s and 2-min respectively. Blocks were performed in the presence of warm (non-painful/control) or hot (pain) thermal stimuli applied to the contralateral forearm. Orders of perceived effort intensity and blocks were randomised. After each trial participants reported acute muscle pain intensity in the exercising forearm and external thermal pain on the contralateral arm. During, force (N), time-force integral (N/s), muscle activation, and cardiorespiratory variables were measured. Repeated measures ANOVAs assessed differences between conditions and trials at each fixed perceived effort intensity.

Results

Intensity × trial interactions showed greater acute muscle pain (F (4.19,159.39) = 12.48, p < .001), a higher peak force (F (1,36) = 213.39, p < .001), and higher time-force integral (F (1,36) = 200.07, p < .001) during the hard versus light fixed perceived effort task. A larger reduction in force (F (4.47,160.73) = 7.99, p = .001) was evident in the hard compared to light fixed perceived effort trials. In the thermal pain (hot) condition, participants produced higher peak force (F (1,38) = 4.84, p = .034) and higher time-force integral (F (1,38) = 6.28, p = .017) compared to the control (warm) condition. While the intensity of the thermal pain stimulation was calibrated to elicit a “strong” pain (50/100) at resting baseline, participants rated a lower thermal pain intensity during the exercise (F (1,38) = 52.53, p < .001), suggesting an exercise-induced hypoalgesia effect.

Conclusions

Preliminary analysis indicates differing effects of natural, acute muscle pain versus external thermal pain on motor behaviour at a fixed perceived effort. Acute muscle pain originating from repeated muscular contractions produced an expected decrease in force production. Naturally, any increases in force would further augment acute muscle pain (Cook et al., 1997). In contrast, thermal pain is associated with increased force production contrary to our hypothesis. It may be that individuals increase force to minimise thermal pain due to a prioritising of effort over pain during a self-regulated task (Vogel et al., 2020). Or it might be that individuals are conscious that thermal pain will remain constant therefore exerting additional force can help distract from the external pain (Torta et al., 2017). A further exploration on the electromyographic and cardiorespiratory changes will yield interesting insights to the varying effects of pain types on perceived effort and motor behaviour.

References

Chowdhury, N., Chang, W., Millard, S., Skippen, P., Bilska, K., Seminowicz, D., & Schabrun, S. (2022). The effect of acute and sustained pain on corticomotor excitability: A systematic review and meta-analysis of group and individual level data. The Journal of Pain, 23(10), 1680-1696. https://www.doi.org/10.1016/j.jpain.2022.04.012
Cook, D. B., O’Connor, P. J., Eubanks, S. A., Smith, J. C., & Lee, M. (1997). Naturally occurring muscle pain during exercise: assessment and experimental evidence. Medicine and Science in Sports and Exercise, 29(8), 999–1012.
Koltyn, K. F. (2002). Exercise-induced hypoalgesia and intensity of exercise. Sports Medicine, 32(8), 477-487. https:/doi.org/10.2165/00007256-200232080-00001
Norbury, R., Smith, S. A., Burnley, M., Judge, M., & Mauger, A. R. (2022a). The effect of elevated muscle pain on neuromuscular fatigue during exercise. European Journal of Applied Physiology, 122(1), 113-126. https://doi.org/10.1007/s00421-021-04814-1
Richter, M., Gendolla, G. H. E., & Wright, R. A. (2016). Three decades of research on Motivational Intensity Theory: What we have learned about effort and what we still don’t know. Advances in Motivation Science, 3, 149-186. https://doi.org/10.1016/bs.adms.2016.02.001
Torta, D. M., Legrain, V., Mouraux, A., & Valentini, E. (2017). Attention to pain! A neurocognitive perspective on attentional modulation of pain in neuroimaging studies. Cortex, 89, 120?134. https://doi.org/10.1016/j.cortex.2017.01.010
Vogel, T. A., Savelson, Z. M., Otto, A. R., & Roy, M. (2020). Forced choices reveal a trade-off between cognitive effort and physical pain. eLife, 9, e59410. https://doi.org/10.7554/eLife.59410

Presenting Author

Callum A. O'Malley

Poster Authors

Callum O'Malley

PhD

University of Exeter

Lead Author

E-mail

M. Bergevin

Université de Montréal, Montreal, Qc, Canada

Lead Author

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Thomas Mangin

Université de Montréal

Lead Author

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Judith Debray

Université de Montréal

Lead Author

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Ilaria Monti

Université de Montréal

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Christopher Fullerton

University of Stirling

Lead Author

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Alexis Mauger

University of Kent

Lead Author

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Pierre Rainville

Université de Montréal

Lead Author

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B. Pageaux

Université de Montréal, Montreal, Qc, Canada

Lead Author

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Topics

  • Models: Acute Pain