Feasibility of unsupervised home-based leg heat therapy in older adults: a pilot sham-controlled trial

The progressive decline in lower-extremity functioning with advancing age curtails independence and is a strong predictor of disability, hospitalizations, and mortality. Structured exercise is the cornerstone for improving functional capacity, but many older adults face barriers to regular physical activity. Accumulating evidence suggests that heat therapy (HT) can counteract age-related declines in cardiovascular and physical function, but the lack of practical heat delivery methods has hindered implementation. Objective and Hypothesis: This pilot randomized, sham-controlled trial aimed to evaluate the feasibility and safety of unsupervised, home-based leg HT using water-circulating trousers in older adults. The primary outcomes were compliance with the HT regimen, completion rates, and device safety. The secondary goals were to examine the effects of leg HT on 6-min walk distance, ankle plantar flexor muscle strength, sit-to-stand performance, blood pressure, quality of life, and the morphology of the calf muscles, as assessed using combined T1-weighted and mDixon magnetic resonance imaging (MRI). We hypothesized that 12 weeks of HT would improve walking performance, increase calf strength, and reduce intramuscular fat compared to a sham intervention. Methods: Twenty-four adults aged ≥65 years who were sedentary and without significant mobility limitations were randomized to HT (n=12) or SHAM (n=12) therapy. Participants in both groups were provided with identical water-circulating trousers, a water circulator, and a portable heater. The water circulator was fitted with an hour meter to record equipment operating time. For the HT group, the heater was set to warm the water to 42ºC, whereas the SHAM heater was programmed to reach a target temperature of 33ºC. Participants were asked to apply the treatment daily for 90 minutes over 12 weeks. The outcomes were assessed at baseline and after the 12-week intervention. Results: Among the twenty-four randomized participants, 4 participants, 2 from SHAM and 2 from HT, withdrew from the study during the intervention period. No serious adverse events occurred, though minor thermal injuries were reported in 4 HT participants. The average compliance was 92±35% in the SHAM group and 93±11% in the HT group (difference between groups: 0.83%, p=0.95, 95% CI -26.94 to 28.60). The HT group showed an average increase of 37±32 meters in the 6-minute walk distance at 12 weeks, compared to an 11±33 meter increase in the sham group, with a trend toward greater improvement in the HT group (+26.11 meters, p=0.09, 95% CI: 4.70 to 56.91). No significant differences were observed in strength, sit-to-stand performance, or calf morphology. Participant-reported BP measurements showed transient reductions (~7/5 mmHg systolic/diastolic) after HT sessions, but no sustained reductions were observed. Conclusion: Unsupervised, home-based leg HT using water-circulating trousers perfused with warm water is both feasible and well-tolerated, with potential to improve walking performance in older adults. These findings suggest that leg HT could be an accessible, at-home intervention to enhance mobility and quality of life in aging populations. Supported by ACSM Foundation, Indiana CTSI (UL1TR002529), and NIA (R01 AG073634-01A1). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.