The magnitude of exercise-induced hypoalgesia can be improved and correlated with endogenous pain modulation following a 4-week treadmill running in female

Objective: This study aimed to investigate the changes in pain perceptions, acute exercise-induced hypoalgesia (EIH), and endogenous pain modulation responses following 4-week treadmill running exercises with different intensities in females. Methods: Forty-two female individuals were randomly assigned to two groups (TRL and TRH) and performed 12 sessions of treadmill running within 4 weeks. Running intensities for each group is 55% of reserve heart rate (HRR) in TRL or 70% HRR in TRH. Before and after each running sessions, the pressure pain thresholds (PPT) and mechanical pain thresholds (MPT) were measured and the difference between pre- and post-running results were calculated as EIH responses. The conditioned pain modulation (CPM) and temporal summation (TS) were also measured at baseline and 24h after final running session. Results: Treadmill running only induced acute EIH responses with all pre-running PPT and MPT remained unaltered. However, the value EIH responses were significantly positively correlated with running sessions in TRL group, and negatively correlated with running sessions in TRH group. And running at low-intensity also showed greater EIH and CPM responses, and lower TS responses than running at high intensity. Besides, the EIH were positively correlated with CPM, and negatively correlated with TS after 12 running sessions. Conclusion: Four-week low-intensity treadmill running may improve acute EIH responses with the enhancement of endogenous pain modulation in healthy females. Meanwhile, CPM and TS may be correlated with EIH and be changed after exercise training, respectively. However, the individuals baseline pain thresholds may remain unaltered and not be affected by EIH or endogenous pain modulation.