Exercise - induced Hypoalgesia in Physically Active Men Following Different Exhaustive Cycle-ergometries

Purpose: The study deals with changes in pressure pain thresholds (PPT) after exhaustive exercises. Two different protocols were applied to trained men of different age groups and the magnitude of exercise induced hypoalgesia (EIH) compared in inactive and loaded muscles.

Methods: 30 healthy and physically active males (15 young and 15 old) completed two exhaustive cycle-exercises with an incremental load test (ILT; 25W x min-1) and a constant load test (CLT) performed at 100% of maximal load during ILT. A control test was performed in order to allow for repeated measurement effects. Before, 1 minute, and 4 minutes after exercise PPT was examined from the middle part of the thenar and the quadriceps. In addition, resting and peak values of heart rate and lactic acid concentration ([lac]) were measured.

Results: Repeated measurements did not influence PPT in the young but had a significant effect in the elderly. After adjusting for this baseline drift, EIH did not significantly differ between young and old subjects. While exercise did not change PPT in the inactive thenar, significant increases occurred in the quadriceps. The reduction in pain sensitivity was significantly (p < 0,01) more pronounced after the constant load test although exercise duration and the total amount of work was significantly lower. Peak heart rate and peak [lac] were comparable in both tests.

Discussion: The amount of EIH after exhaustive, dynamic exercise does not depend on age in healthy and physically active males. The magnitude of hypoalgesia appears, at least in part, independent of metabolism or the sympathetic drive during exercise.

Conclusion: Cycling until exhaustion leads to hypoalgesia in exercising muscles. However, the amount of EIH is not uniform but depends on the exercise protocol.