Author(s): SMITH, S., DUAN, B., MAUGER, A.R., Institution: UNIVERSITY OF KENT, Country: UNITED KINGDOM, Abstract-ID: 2590

INTRODUCTION:
Naturally occurring exertional pain in the exercising muscle is inherent to exercise participation. The subjective experience of this pain is shaped by complex processes, where nociceptive input is modified through endogenous pain modulation and is influenced by factors such as age, sex, psychological, biological, and lifestyle variables (e.g., physical activity). However It remains unclear which factors most predict an individual’s capacity to modulate pain endogenously. Conditioned pain modulation (CPM), where test stimulus (TS) pain is compared before and after the administration of a conditioning stimulus (CS), provides a dynamic assessment of endogenous pain inhibitory capacity. Yet CPM protocols are typically applied in the upper body, with limited evidence for lower-limb paradigms relevant to locomotive exercise. This study examined the demographic, anthropometric, psychological, and lifestyle factors that predict lower-limb CPM in recreationally active adults.
METHODS:
A sample of n = 30 (19 males, 11 females) healthy recreationally active adults completed a repeated-measures CPM protocol across a familiarisation visit followed by three experimental visits. A sequential protocol was employed with pressure pain threshold (PPT) on the right rectus femoris as the TS and ischemic cuff occlusion around proximal portion of the left leg as the CS. CPM effect was quantified relative to baseline, and the final CPM value was calculated as the average across the three visits. Participant demographics, anthropometrics, psychological traits and states, and physical activity were also collected. The relationship between these variables and CPM was measured using Pearson and Spearman bivariate two-tailed correlations, followed by hierarchical regression analysis to examine the predictive capacity of significant correlations while controlling for participant age.
RESULTS:
Spearman’s correlation analysis revealed a significant moderate negative correlation between present-moment negative affect and CPM (r = -0.417, p = 0.022). No other variables were significantly associated with CPM (p > 0.05). A multiple regression model including age and present-moment negative affect was significant (F(2,27) = 4.53, p = 0.020), explaining 25.1% of the variance in CPM. Age was a significant predictor of CPM (B = 0.779, p = 0.023), whereas present-moment negative affect was not (B = -1.222, p = 0.103) and did not explain additional variance beyond age (ΔR² = 0.079, p = 0.103).
CONCLUSION:
Age was the only significant predictor of endogenous pain modulation, with older participants exhibiting greater pain inhibition. Present-moment negative affect was not a significant predictor of negative affect, and all other measured variables were not significantly associated with CPM. These findings indicate that variability in lower-limb CPM within this sample is primarily explained by age, and future research could investigate additional factors influencing endogenous pain modulation across the adult lifespan.