Is low intensity exercise sufficient to induce exercise-induced pain threshold modulation in people with persistent pain?

OBJECTIVES

We investigated whether a 12-min walk test (12MWT) yielded exercise-induced pain threshold modulation (EIPM) within people with persistent pain and whether baseline self-report and pain sensitivity measures differed according to these responses.

DESIGN

Cross-sectional study.

METHODS

Two cohorts (tertiary/community) (n = 88) with persistent pain underwent pressure pain threshold (PPT) testing before and after a 12MWT to determine exercise-induced pain threshold modulation responses. Baseline self-report (pain severity, pain distribution, psychological distress, sleep) and baseline widespread pain sensitivity (WPS) (high/low) were recorded. Within and between-group differences were analysed using paired t-tests and repeated measure analyses of covariance. Individual EIPM responses were categorised as hyperalgesic, no change and hypoalgesic responses. Differences in baseline self-report and pain sensitivity measures between EIPM categories were investigated.

RESULTS

No significant within- or between-group differences in PPT following the 12MWT were detected (p > 0.05). Individual responses showed that up to 30% of the community and 44% of the tertiary cohort demonstrated >20% change in PPT (in either direction). Significant differences were shown in pain distribution (p = 0.002) and baseline WPS (p = 0.001) between people with hyperalgesic, no change, hypoalgesic responses. People with 4-5 pain regions were more likely hyperalgesic (χ2 = 9.0, p = 0.003); people with low baseline WPS were more likely to demonstrate no change (p = 0.002).

CONCLUSION

Low or self-selected intensity exercise was insufficient to induce exercise-induced pain modulation at group level. Individual responses were variable with pain distribution and baseline WPS differing between responses. Future research could evaluate responses and associated factors in larger samples with high baseline pain sensitivity specifically.

Similar effects of fatigue induced by a repetitive pointing task on local and remote light touch and pain perception in men and women

Background

Women involved in repetitive, fatiguing, jobs develop more neck and/or shoulder musculoskeletal disorders than men. Sex differences in the pain response to exercise could contribute to the higher prevalence of neck/shoulder musculoskeletal disorders in women. The objective of this study was to assess sex differences in pain sensitivity following a fatiguing upper limb task. Relationships between measures of fatigue and of the sensitivity to nociceptive and to non-nociceptive stimulations were also explored.

Methods

Thirty healthy adults (15 women) performed a fatiguing repetitive pointing task with their dominant arm. Upper limb electromyography was recorded from the dominant upper trapezius, anterior deltoid and bicep brachii and from the contralateral tibialis anterior. Before and immediately after the repetitive pointing task, pressure pain and light touch sensitivity thresholds were measured over the same muscles.

Results

Electromyographic signs of fatigue were observed only in the anterior deltoid and biceps brachii muscles. Pressure pain thresholds over both muscles increased slightly (effect size ≤ 0.34), but no changes occurred over the upper trapezius and the tibialis anterior. Light touch thresholds increased moderately to importantly after the repetitive pointing task over all four muscles (effect sizes = 0.58 to 0.87). No sex differences were observed in any sensory variable. Moreover, no or weak correlations (r = -0.27 to 0.39) were observed between electromyographical signs of fatigue, light touch threshold and pressure pain threshold variables.

Conclusions

We observed sex-independent effects of a repetitive upper limb task on the sensitivity to painful and to nonpainful stimuli. Moreover, the hypoalgesia induced by the repetitive pointing task was weak and localized, and did not directly correlate with the induced muscle fatigue. Results suggest that fatigue-related changes in the sensitivity to noxious and innocuous stimuli could not explain women’s greater prevalence of neck/shoulder musculoskeletal disorders.

Exercise-induced hypoalgesia after acute and regular exercise: experimental and clinical manifestations and possible mechanisms in individuals with and without pain

This review describes methodology used in the assessment of the manifestations of exercise-induced hypoalgesia in humans and previous findings in individuals with and without pain. Possible mechanisms and future directions are discussed.

Exercise and physical activity is recommended treatment for a wide range of chronic pain conditions. In addition to several well-documented effects on physical and mental health, 8 to 12 weeks of exercise therapy can induce clinically relevant reductions in pain. However, exercise can also induce hypoalgesia after as little as 1 session, which is commonly referred to as exercise-induced hypoalgesia (EIH). In this review, we give a brief introduction to the methodology used in the assessment of EIH in humans followed by an overview of the findings from previous experimental studies investigating the pain response after acute and regular exercise in pain-free individuals and in individuals with different chronic pain conditions. Finally, we discuss potential mechanisms underlying the change in pain after exercise in pain-free individuals and in individuals with different chronic pain conditions, and how this may have implications for clinical exercise prescription as well as for future studies on EIH.