Training load and pain response during progressive resistance training in patients with hip osteoarthritis in the PROHIP trial

Objective: To describe training load and repetitions, illustrate the pre- and post-exercise hip pain intensity trajectories throughout a 12-week progressive resistance training (PRT) program, and evaluate the difference in change in pre-exercise hip pain intensity between high and moderate-to-low adherence to PRT among individuals with severe hip osteoarthritis and indication for surgery. Design: Secondary analysis of a randomized controlled trial reporting data only from participants who were enrolled from September 2019 through June 2021 from four orthopedic departments in Denmark and assigned to PRT. Patient-reported hip pain intensity at rest was measured before and after each session using a Numerical Rating Scale (NRS) ranging from 0 (no pain) to 10 (worst pain imaginable). High adherence was defined as attending at least 18 of 24 scheduled sessions. Results: A total of 55 participants (mean age 67.7 years and 51 ​% females) received PRT. Training load increased while repetitions decreased from week 1 to week 12. The mean pre-exercise NRS decreased from 3.18 points at baseline to 2.13 points at 12-weeks (difference, 1.05 points [95%CI 0.46, 1.65]). The mean post-exercise NRS decreased from 2.87 points at baseline to 2.04 points at 12-weeks, (difference, 0.83 points [95%CI 0.30, 1.37]). There was no significant difference in mean change in pre-exercise NRS scores between high and moderate-to-low adherence (group difference, 1.08 points [95%CI -0.85, 3.02]). Conclusions: Individuals with severe hip osteoarthritis and indication for surgery can exercise at progressively higher intensity while maintaining low hip pain intensity. High adherence did not result in greater pain relief. Clinical trial registration number: NCT04070027.