The feasibility and acceptability of high-intensity interval training for adults with mental illness: A pilot study

Adults with mental illness have increased risk of cardiovascular disease. High-intensity interval training (HIIT) is more efficacious than moderate-intensity continuous training (MICT) for improving cardiorespiratory fitness (CRF); however, the utility of HIIT for this group is unclear. The aim of this study was to compare the feasibility and acceptability of HIIT and MICT in adults with mental illness. A secondary aim was to compare the efficacy of HIIT and MICT on mental health and fitness. Inactive adults with self-reported mental illness participated in aerobic exercise three times/week over 12 weeks. Participants were randomised to HIIT (3x4-min bouts at 85–95% peak heart rate [HRpeak] interspersed with 3-min recovery bouts) or MICT (1 × 30-min at 65–75% HRpeak). Feasibility was assessed using attendance and withdrawal rates. Acceptability and mental health was assessed using self-administered questionnaires. Fitness was measured using indirect calorimetry during a graded fitness test to exhaustion. 24 participants consented and 16 participants began the intervention (HIIT, n = 8; MICT, n = 8). Completion rates (HIIT, n = 4; MICT, n = 5) and median attendances were similar (HIIT = 81%, MICT = 86%). Most participants were satisfied with their allocation (88% MICT; 100% HIIT), and found the exercise enjoyable (63% MICT; 100% HIIT). Equal numbers reported that they would like to continue the exercise (63%), and that they would feel confident doing so without supervision (75%). No significant differences were found between groups on mental health and fitness. This preliminary evidence suggests that HIIT was as acceptable and feasible as MICT for adults with mental illness.