Perceptual and hypoalgesic responses to submaximal knee extension exercise with different pressures and modes of blood flow restriction: Effect of estimated muscle metabolites.

Abstract

Purpose: To investigate the effects of exercise-induced metabolites on the perceptions of pain and fatigue.

Method: Fifty-three adults completed six visits. The first visit involved multiple baseline tests, including a blood-flow-restricted exercise performance test (i.e., 2 sets of knee extension to task-failure at 30% 1RM with 80% arterial occlusion pressure [AOP]). In subsequent visits, participants performed five experimental conditions in a randomized order: 1) time-matched, non-exercise control (Control) and four low-load exercise conditions with either 2) 80%AOP (LL+80%), 3) 40%AOP (LL+40%), 4) intermittent 80%AOP (LL+80%Int), or 5) no blood flow restriction (0 mmHg; LL). Three-minute post-exercise circulatory occlusion (PECO) was employed to assess the effect of pooled muscle metabolites on perceived pain and fatigue and pain sensitivity (via pressure pain threshold). The results from liner mixed model are presented as mean [95% confidence interval].

Results: Condition-by-time interactions were found for perceived pain (P < 0.001) and fatigue (P < 0.001). LL+80% elicited higher increase in thigh pain (2.7 [2.2, 3.1] AU) and fatigue (2.1 [1.7, 2.5] AU) compared to LL+40%, LL+80%Int, and LL. Pain and fatigue did not change differently during PECO but declined three minutes post-PECO in exercise conditions (except fatigue in LL+80%Int). There was evidence of an interaction for pressure pain threshold of the tibialis anterior but not the forearm.

Conclusion: Continuous blood flow restriction with higher pressure (80%AOP) augmented the pain and fatigue perceptions from submaximal unilateral knee extension exercise, arguably through muscle metabolite accumulation (estimated by PECO). Conflicting evidence existed for blood flow restricted exercise-induced hypoalgesia, possibly confounded by PECO.