Brendon H. Roxburgh1, 2, 3, Holly A. Campbell1, 3, Rebecca Goodman1, James D. Cotter2, 3, Ulla Reymann1, David Gwynne-Jones1, 4, Kate N. Thomas, PhD1, 3. Acute and Adaptive Analgesic Effects of Passive Heat Therapy or High-Intensity Interval Exercise in Patients with Severe Lower-Limb Osteoarthritis: A Mixed-Methods Exploratory

Study1Department of Surgical Sciences, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand. 2School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand. 3HeartOtago, University of Otago, Dunedin, New Zealand. 4Department of Orthopaedic Surgery, Dunedin Hospital, Southern District Health Board, Dunedin, New Zealand.


Background: The purpose of the study was to examine the acute and adaptive analgesic effects of two separate therapies – hot-water immersion and upper-limb high-intensity interval exercise (HIIE) – in patients with severe lower-limb osteoarthritis. Methods: Eligible and consenting participants scheduled for hip or knee arthroplasty were randomized to hot-water immersion (Heat, n=27); 20-30 min immersed in 40∞C water followed by ~15 min light resistance exercise) or upper-limb high-intensity interval exercise (HIIE, n=25; 6-8 x 60 s intervals on a cross-trainer or arm ergometer at ~100% peak V̇O2, 60-90 s recovery); all for 36 sessions (3 sessions per week for 12 weeks). Joint pain (0-10 scale; 0 = no pain, 10 = worst pain) and accelerometry were assessed during and following acute exposure and across the intervention. Results: Joint pain decreased by 3 arbitrary units (AU) and 2 AU during an acute exposure of heat therapy and HIIE (p≤0.035); this acute analgesic effect was still evident in the final week of the intervention. These acute analgesic effects did not translate to reduced joint pain adaptively across the intervention (p=0.684), or improved daily step count in the 24-h following acute exposure (p=0.855) or across the intervention (p=0.604). Conclusions: The findings from this study highlight the acute analgesic effects of hot-water immersion and HIIE, and that patients with severe lower-limb osteoarthritis can participate in high-intensity upper-limb exercise, relatively pain free. Significance: This research reports several novel findings: 1) acute hot-water immersion has a potent analgesic effect in people with severe lower-limb osteoarthritis; 2) this acute effect is lost within one hour of exposure; 3) people with severe lower-limb osteoarthritis can perform cardiovascularly meaningful exercise via HIIE using predominantly the upper limbs, while decreasing joint pain; 4) reassuringly, the acute analgesic effect of hot-water immersion or HIIE persists across 12-wk of repeated exposure.