Effects of 4-Week Treadmill Running at Different Intensities on Exercise-Induced Hypoalgesia and Endogenous Pain Modulation in Healthy Individuals.

All exercise groups exhibited an exercise-induced hypoalgesia (EIH) effect following 4-week treadmill running sessions.

• All groups showed a significant EIH effect (p < 0.001, F = 9.424)
• Pressure pain thresholds (PPTs) and mechanical pain thresholds (MPTs) increased during running sessions (p = 0.004, F = 2.084)
• 56 healthy individuals were randomly assigned to a control group and three experimental groups: high intensity (TRH), moderate intensity (TRM), and low intensity (TRL)
• Participants completed 12 treadmill running sessions within 4 weeks based on target heart rate (THR)

The moderate and low intensity treadmill running groups showed significantly higher PPT and MPT increases compared to the high intensity group.

• TRM and TRL groups were significantly higher than the TRH group (p < 0.001)
• This suggests that lower-to-moderate intensity exercise produces greater pain threshold improvements than high intensity exercise
• PPT and MPT were assessed following regular treadmill running across all groups

Conditioned pain modulation (CPM) significantly increased in the moderate and low intensity treadmill running groups after 4 weeks.

• CPM of the TRM and TRL groups significantly increased (p < 0.001)
• The TRH group did not show a significant increase in CPM
• CPM is a measure of endogenous pain inhibition assessed following regular treadmill running sessions

Temporal summation (TS) significantly decreased only in the moderate intensity treadmill running group.

• TS of the TRM group significantly decreased (p < 0.001)
• The TRL and TRH groups did not show significant changes in TS
• A decrease in TS indicates reduced central sensitization or enhanced pain inhibition

Acute EIH responses were positively correlated with CPM and negatively correlated with temporal summation.

• EIH-A was positively correlated with CPM (r = 0.724, p < 0.001)
• EIH-L was positively correlated with CPM (r = 0.726, p < 0.001)
• EIH-M was positively correlated with CPM (r = 0.347, p = 0.009)
• EIH-A was negatively correlated with TS (r = -0.529, p < 0.001)
• EIH-L was negatively correlated with TS (r = -0.544, p < 0.001)

The study design involved a pre-assessment running evaluation administered 1 week before the 4-week intervention period.

• A running assessment was administered 1 week before running sessions
• The study included 56 healthy individuals randomized to four groups
• Exercise intensity was based on target heart rate (THR)
• The trial was registered at ClinicalTrials.gov with identifier ChiCTR2300074367