Pain Decreases During Exercise Using The Principles Of Offset Analgesia

Offset analgesia (OffA) is a disproportionate decrease in pain following a small decrease in noxious stimulus intensity. OffA has been used to investigate endogenous pain inhibition but has not been translated to exercise prescription for therapeutic use. It is unknown if pain during exercise can be modulated with OffA and how this relates to affective valence (feelings of pleasure-displeasure). PURPOSE: The aims of this study are to investigate 1) if OffA can be elicited with an experimental exercise task and 2) if OffA is related to affective valence. METHODS: In two randomized experimental sessions (control or offset exercise), 43 young healthy adults (22.7 ± 4.5 years; 23 women) performed a seated, sustained, isometric knee extension exercise task at 25% of maximal voluntary contraction (MVC) force until reporting 5/10 pain in the exercising muscle group at which point either the control or offset portion of the exercise task began. For the control task, participants continued to maintain the force for 25 seconds. For the offset task, force was increased to 50% MVC for 10 seconds before returning to the initial force (25% MVC). Pain reports, using the 0-10 Numerical Rating Scale (NRS), were taken 5 and 20 seconds after reporting 5/10 pain for both exercise tasks. OffA was calculated, using a standard protocol, as a percent decrease in pain ratings when comparing the offset task to the control task [(pain during control test at 20 seconds/pain during control test at 5 seconds)*100 - (pain during offset test at 20 seconds/pain during offset test at 5 seconds)*100]. At the end of each session, participants used the Feeling Scale (-5 to +5) to rate their feelings during the last 10 seconds of both exercise tasks. RESULTS: Participants reported 30.1% (± 30.8%) decrease in pain ratings (average decrease from 7 to 4 on the NRS) with the experimental offset exercise task compared to the control exercise task (6 to 7 NRS), with more positive feelings during the final 10 seconds of the offset task (M = 1.44, ± 2.35) compared with the control task (M = 0.07, ± 2.36, p = 0.009). There was a positive correlation between OffA and the difference in feeling rating between tasks, r = 0.47 (p = 0.005). CONCLUSION: The principles of OffA can be translated to therapeutic exercise potentially improving exercise tolerance and feelings toward exercise.