Introduction: The purpose of the study was to compare pain ratings and thresholds in men and women before and after isometric contractions of varying intensity and duration performed with the elbow flexor muscles.
Methods: Pain perception was assessed, using a pressure device applied to the contralateral finger, before and after the following isometric contractions: 1) three brief maximal voluntary contractions (MVC), 2) 25% MVC sustained until task failure, 3) 25% MVC sustained for 2 min, and 4) 80% MVC sustained until task failure.
Results: High-intensity and long-duration, low-intensity isometric contractions produced an analgesic response. The greatest change in pain threshold and pain ratings, when pressure was applied to the contralateral finger, was after the long-duration, low-intensity contraction sustained until failure. Sex differences were present with women reporting 1) lower pain thresholds and higher pain ratings during quiet rest and 2) higher pain ratings before and after isometric contractions.
Conclusion: These results suggest that activation of high-threshold motor units is involved in exercise-induced analgesia.