Sub-maximal endurance exercise does not mediate alterations of somatosensory thresholds

Abstract

physical exercise has been shown to alter sensory functions, such as sensory detection or perceived pain. However, most contributing studies rely on the assessment of single thresholds, and a systematic testing of the sensory system is missing. this randomised, controlled cross-over study aims to determine the sensory phenotype of healthy young participants and to assess if sub-maximal endurance exercise can impact it. We investigated the effects of a single bout of sub-maximal running exercise (30 min at 80% heart rate reserve) compared to a resting control in 20 healthy participants. The sensory profile was assessed applying quantitative sensory testing (QST) according to the protocol of the German Research Network on Neuropathic Pain. QST comprises a broad spectrum of thermal and mechanical detection and pain thresholds. it was applied to the forehead of study participants prior and immediately after the intervention. time between cross-over sessions was one week. Submaximal endurance exercise did not significantly alter thermal or mechanical sensory function (time × group analysis) in terms of detection and pain thresholds. The sensory phenotypes did not indicate any clinically meaningful deviation of sensory function. the alteration of sensory thresholds needs to be carefully interpreted, and only systematic testing allows an improved understanding of mechanism. in this context, sub-maximal endurance exercise is not followed by a change of thermal and mechanical sensory function at the forehead in healthy volunteers. Exercise-induced changes of the somatosensory profile have led to controversial discussions, in particular with regards to their effect on pain. Exercise has been shown to induce hypoalgesia in healthy subjects 1 , however, it can also induce hyperalgesia in certain chronic diseases or following exertion 2. Its effects in people with clinical pain are rather variable. In patients with neuropathic pain, exercise is considered to improve nerve function, reduce pain and other sensory dysfunction, and improve static and dynamic functional mobility 3. However, in patients with musculoskeletal pain, manual therapies on stability failed to achieve a significant pain reduction 4. A recent systematic review suggests an association between psychosocial factors and exercise-induced hypoalgesia in healthy subjects, and in patients with musculoskeletal pain 5. This is further supported by a proposed central mechanism underlying these two phenomena, such as the increased activation of NMDA receptors in pain-modulating areas 6. Exercise-induced hypoalgesia, i.e. pain reduction, can be achieved by both aerobic and resistance training, of which the latter achieves larger mean effect sizes 7. Aerobic exercise is more likely to induce generalised hypoalgesia, whereas resistance exercise is related to locoregional effect sites 1. Higher aerobic intensities (200 W or 60-75% oxygen uptake) appear more effective in mediating hypoalgesia. Isometric exercise was shown to decrease the intensity of experimental pain at lo...

Quantitative Sensory Changes Related to Physical Activity in Adult Populations

“…The range of QST procedures was well-represented but widely variable in application across included studies. The German Research Network DFNS protocol was used in only 2 of 196 included studies, confirming that QST application related to physical activity is largely unstandardized 52,53 . As QST can involve a range of potential assessments, each targeting different underlying pain neuromodulatory mechanisms, it is possible that this observed heterogeneity reflects differing study intentions.…”

“…The German Research Network DFNS protocol was used in only 2 of 196 included studies, confirming that QST application related to physical activity is largely unstandardized. 52,53 As QST can involve a range of potential assessments, each targeting different underlying pain neuromodulatory mechanisms, it is possible that this observed heterogeneity reflects differing study intentions. Although the use of a standardized approach would improve between-study comparisons, it may not always be feasible to incorporate all of the German Research Network DFNS protocol recommendations.…”

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“…Repetitive stress, as induced by forced swimming, has been shown to induce thermal hyperalgesia by diminishing central serotonin activity ( Quintero et al, 2000 ). Still, hyperalgesia seems to occur in exhaustive states of exercise (i.e., maximum of stress) ( Kortenjann et al, 2020 ), and moderate physical activity is an important component of effective chronic pain management ( Rice et al, 2019 ). When looking at this interaction it is also necessary to pay attention to the HPA-axis which has a potential anti-inflammatory effect via cortisol (thus reducing cytokines).…”