Exercise Induced Analgesia But Not Mood State Varies With Exercise Intensity.

Abstract

The analgesic and psychoactive effects of exercise (EX) are well established. Despite this, the EX intensity needed to elicit an optimal effect on these phenomena is unknown. PURPOSE: To compare the effect of EX intensity on post EX analgesia and subjective psychoactive mood state. METHODS: Six subjects (1 male; 5 females; age = 20.6 ± 0.8 yrs) were tested for maximal aerobic exercise capacity (VO2max) using a graded cycling test. Following the VO2max, each subject was studied once a week using control conditions or 45%, 65% and 75%-85% of their VO2max in randomized order. Each EX bout lasted 30 mins and consisted of a 5-min warm-up, 20-mins at the assigned EX workload and a 5-min cooldown. The control session consisted of 30-mins of sitting on a cycle with no EX. EX analgesia was assessed by finding minimal pain threshold (MPT) before and following EX using a pain algometer on the extensor carpi radialis and was measured in Newtons (N). The Psychoactive Effects Questionnaire (PEQ), comprised of 36 questions that assess the subjective dopaminergic effects associated with the effects psychoactive drugs, was administered before and after EX. Blood lactate (BL) was also assessed at the same timepoints as MPT and PEQ. Breath by breath oxygen consumption was measured during EX using indirect calorimetry. Change in (Δ) MPT and PEQ (PreEX vs PostEX) was quantified using a two-tailed Student’s T-Test. The effect of EX intensity on MPT and PEQ was assessed by a one-way repeated measures ANOVA. Data are shown as mean ± SEM. RESULTS: BL increased in a linear fashion in response to increased EX intensity (R = 0.50; p < 0.001). Control MPT was 29.8 ± 2.1 N. There was a change in MPT, following each EX session (Control vs. 45% = 37.6 ± 1.4; 65% = 39.5 ± 0.5; 85% = 42.9 ± 1.1; p < 0.05). EX at 75%-85% had a greater impact on MPT relative to the 45% (85% = 13.02 ± 1.0 ∆N vs. 45% = 7.8 ± 1.5 ∆N; p < 0.05) session but not the 65% session (9.5 ± 1.5 ∆N; p > 0.05). There was no difference between the 45% and 65% EX session (p > 0.05). PEQ was significantly increased following EX by 118 ± 12.1% (p < 0.05). Unlike MPT, PEQ did not change dependent upon the intensity of the EX session (p < 0.05). CONCLUSION: Higher intensity EX (85% VO2max) appears to elicit a greater analgesic effect relative to lower intensity (45% VO2max). While EX increases PEQ it does not appear to be sensitive to EX intensity.