Background & Aims
Exercise-induced hypoalgesia (EIH) refers to an acute experimental pain reduction following a single bout of exercise [1]. The mechanisms underlying EIH are still elusive [1,2] and there is inconsistency in the literature as to 1) whether EIH differentially impacts the perception of different types of nociceptive stimuli (e.g. pressure vs. thermal stimuli) [3,4] and 2) whether exercise selectively modulates pain at exercising body parts, or also involves non-exercising body parts [5,6]. In this study, we aimed to characterize the effects of a single session of aerobic exercise on the sensitivity to stimuli activating skin vs. muscle nociceptors, within or outside exercising body parts. This characterization is a crucial first step to clarify the mechanism(s) that drive EIH. Indeed, some of the mechanisms proposed to explain EIH can be expected to modulate nociception regardless of modality and location, whereas other mechanisms predict local changes restricted to the exercising muscle.
Methods
We recruited 40 healthy males (18-30 years) who underwent sensory assessments before and after a cycling exercise (25 min at 75% of the Heart Rate Reserve) or a control condition (25 min of minimal-effort cycling) in two counterbalanced sessions. Stimuli recruiting deep-tissue nociceptors (pressure pain threshold, PPT [7]), nociceptive and non-nociceptive thermo-sensitive cutaneous afferents (contact heat pain threshold [HPT], cold detection threshold [CDT] [8]), skin mechanosensitive nociceptors (mechanical pinprick pain rating, PP [9]) were delivered over the dominant rectus femoris muscle (exercising site) and over the flexor muscles of the non-dominant forearm (non-exercising site). The sensitivity to non-somatosensory stimulation (auditory detection threshold, ADT) was also determined. The impact of exercise on the values of each sensory test at each site was quantified as [(post-pre) exercise – (post – pre) control].
Results
We analyzed data from 38 participants (23.8 ± 3.7 years). Using a linear mixed model, we found a statistically significant interaction between the test modality PPT and the site Quadriceps (estimate = 6.217 N/cm2; p <0.05). No impact of exercise was found on ADT, CDT, HPT, PP at neither the quadriceps nor the forearm.
Conclusions
We found that, in healthy young adult males, a cycling aerobic exercise reduces pain induced by blunt pressure solely at the exercising body part. No impact of exercise, regardless of the testing site, was found on the sensitivity to stimuli recruiting nociceptive and non-nociceptive thermal and mechanical cutaneous afferents or auditory stimuli. These findings suggest a contribution of local changes in muscle nociceptor sensitivity to EIH, narrowing down its potential mechanisms. Further research on these changes is needed to clarify the underlying processes and to observe whether they apply to other populations.
References
1.Vaegter, H. B. & Jones, M. D. Exercise-induced hypoalgesia after acute and regular exercise: experimental and clinical manifestations and possible mechanisms in individuals with and without pain. Pain Rep 5, e823 (2020).
2.Rice, D. et al. Exercise-Induced Hypoalgesia in Pain-Free and Chronic Pain Populations: State of the Art and Future Directions. The Journal of Pain 20, 1249–1266 (2019).
3.Jones, M. D., Nuzzo, J. L., Taylor, J. L. & Barry, B. K. Aerobic Exercise Reduces Pressure More Than Heat Pain Sensitivity in Healthy Adults. Pain Medicine 20, 1534–1546 (2019).
4.Samuelly-Leichtag, G., Kodesh, E., Meckel, Y. & Weissman-Fogel, I. A Fast Track to Hypoalgesia – The Anaerobic Exercise Effect on Pain Sensitivity. Int J Sports Med 39, 473–481 (2018).
5.Vaegter, H. B., Handberg, G., Jørgensen, M. N., Kinly, A. & Graven-Nielsen, T. Aerobic exercise and cold pressor test induce hypoalgesia in active and inactive men and women. Pain Med 16, 923–933 (2015).
6.Micalos, P. S. & Arendt-Nielsen, L. Differential pain response at local and remote muscle sites following aerobic cycling exercise at mild and moderate intensity. Springerplus 5, 91 (2016).
7.Graven-Nielsen, T., Mense, S. & Arendt-Nielsen, L. Painful and non-painful pressure sensations from human skeletal muscle. Exp Brain Res 159, 273–283 (2004).
8.Arendt-Nielsen, L. & Chen, A. C. N. Lasers and other thermal stimulators for activation of skin nociceptors in humans. Neurophysiol Clin 33, 259–268 (2003).
9.van den Broeke, E. N. et al. Characterizing pinprick-evoked brain potentials before and after experimentally induced secondary hyperalgesia. J Neurophysiol 114, 2672–2681 (2015).
Presenting Author
Vladimir Aron
Poster Authors
Topics
- Lifestyle Issues: Sleep/Diet/Exercise/Social Interactions