Conditioned pain modulation predicts exercise-induced hypoalgesia in healthy adults.

INTRODUCTION: Conditioned pain modulation (CPM) is the concept that pain inhibits pain and has potential rehabilitation implications for exercise prescription. The purpose of this study was to determine whether changes in pressure pain perception after a thermal conditioning stimulus (i.e., CPM) was attenuated with aging and whether CPM predicted pain relief after exercise (exercise-induced hypoalgesia (EIH)) in healthy young and older adults. METHODS: Twenty young (21.9 ± 3.3 yr, 10 men) and 19 older (72.0 ± 4.5 yr, 10 men) adults participated in three sessions: one familiarization and two experimental (EIH and CPM) sessions. Pressure pain perception was assessed using a weighted Lucite edge placed on the right index finger for 1 min. EIH was determined by measuring pressure pain perception before and after prolonged submaximal isometric contraction of the elbow flexors. CPM was assessed by measuring pressure pain perception at the finger while the foot was immersed in neutral water versus painful ice water. RESULTS: Young, but not older, adults reported a decrease in pressure pain at the finger while their foot was immersed in the ice water bath compared with the neutral bath (i.e., CPM, trial-age: P = 0.001). Pressure pain ratings decreased after exercise (P = 0.03) that was perceived as painful (peak arm pain, 7.0 ± 3.3) for both young and older adults. Regression analysis showed that after controlling for age and baseline pain, CPM predicted EIH (model adjusted R = 0.23, P = 0.007). CONCLUSIONS: CPM was attenuated in older adults, as measured with a noxious pressure stimulus after a thermal conditioning stimulus, and adults with greater CPM were more likely to report greater EIH.

Pain relief after isometric exercise is not task-dependent in older men and women.

INTRODUCTION: This study assessed the effect of isometric contractions that varied in intensity and duration on pain perception in adults older than 60 yr. METHODS: Pain perception was measured in 24 men and women (mean ± SD age = 72.2 ± 6.2 yr) using a pressure pain device applied to the right index finger before and after isometric contractions of the left elbow flexor muscles of the following doses: 1) three brief maximal voluntary contractions (MVC), 2) 25% MVC held for 2 min, and 3) 25% MVC held to task failure. RESULTS: Older adults reported increased pain thresholds (58 s vs 49 s, P < 0.001) and decreased pain ratings (2.8 vs 3.4, P < 0.001) after exercise, and these changes were similar across all three tasks (P = 0.94 and P = 0.55, respectively). Sex differences were identified with older women reporting greater pain sensitivity (lower pain thresholds [P = 0.01] and higher pain ratings [P = 0.004]) and larger reductions in pain ratings than men (23% vs 9%, P = 0.003) after isometric contractions. CONCLUSIONS: Older adults experienced similar reductions in pain after several different intensities and durations of isometric contractions. Both older men and women experienced increases in pain threshold, but only older women experienced reductions in pain ratings.