Sex Differences in Exercise-Induced Hypoalgesia

Sex Differences in Exercise-Induced Hypoalgesia Following Aerobic Exercise Using a Lower-Limb Cycle Ergometer: A Quasi-Experimental Study

Exercise-induced hypoalgesia (EIH) refers to the reduction in pain sensitivity following acute exercise. Although aerobic exercise has been shown to induce hypoalgesia in healthy individuals, it remains unclear whether the magnitude of this response differs between men and women.

This quasi-experimental study aims to evaluate sex differences in pressure pain thresholds following a standardized aerobic exercise protocol using a lower-limb cycle ergometer. Pressure pain thresholds will be assessed before exercise, immediately after exercise, and 30 minutes after exercise in healthy adults aged 18 to 65 years.

The findings of this study may contribute to improving individualized exercise prescription strategies based on sex differences in pain modulation.

Exercise-induced hypoalgesia (EIH) is characterized by a transient reduction in pain sensitivity following acute physical exercise, measurable through pressure pain thresholds (PPTs). Aerobic exercise has been consistently shown to increase PPTs in healthy individuals through activation of endogenous pain inhibitory mechanisms, including opioid and non-opioid pathways.

However, the influence of biological sex on EIH remains unclear, and understanding potential differences between men and women could have important implications for exercise prescription in clinical and healthy populations.

This quasi-experimental study will include healthy male and female participants aged 18-65 years. Participants will undergo a single session of aerobic exercise on a lower-limb cycle ergometer at 70% heart rate reserve for 30 minutes.

Pressure pain thresholds will be assessed using a validated digital pressure algometer at:

• Quadriceps muscle (local site)
• Lateral epicondyle region (remote site)

Measurements will be performed at three time points:

• Pre-exercise
• Immediately post-exercise
• 30 minutes post-exercise

The primary analysis will compare changes in pressure pain thresholds between men and women using ANCOVA models adjusting for baseline values.

Inclusion Criteria:

• Healthy male and female adults
• Age between 18 and 65 years
• Able to perform moderate-to-vigorous aerobic exercise
• Able to understand study procedures
• Cleared for exercise participation using the Physical Activity Readiness Questionnaire (PAR-Q).

Exclusion Criteria:

• Cardiovascular, respiratory, neurological, or metabolic diseases contraindicating exercise
• Current musculoskeletal pain or injury
• Analgesic medication use within 24 hours prior to testing
• Vigorous exercise within 24 hours prior to testing
• Any contraindication to aerobic exercise