High-intensity interval training outperforms moderate exercise to improve aerobic capacity in patients with recent-onset idiopathic inflammatory myopathies: a multicentre randomised controlled trial.

BACKGROUND: To investigate efficacy, safety, and tolerance of high-intensity interval training (HIIT) vs. clinical standard low-moderate intensity home-based exercise (CON) to improve aerobic capacity, muscle endurance, and mitochondrial function in patients with recent onset, idiopathic inflammatory myopathies (IIM). METHODS: Twenty-three patients with recent onset IIM were randomised into HIIT or CON groups. Both groups underwent 12 weeks of exercise training. The HIIT did 3 sessions/week, always supervised during the first three weeks. Then, training was supervised 1-3 session per week based on an individual assessment of the participants' preference and ability to perform HIIT in the clinic. The CON received one supervised session and then exercised five days per week at home, following clinical standard. Primary outcome was maximal exercise test (VO2peak l/min and ml/kg x min, peak power (Watt), time-to-exhaustion TTE min/sec), with secondary outcomes mitochondrial protein expression in muscle. Safety was assessed by disease activity (serum levels of muscle enzymes, muscle strength (MMT8), Physician Global Assessment, pain, and fatigue (VAS, 0-100). FINDINGS: HIIT resulted in a 16% increase in VO2peak L/min, significantly higher than the 1.8% change in CON (95% CI 0.1; 0.47). Peak power and TTE improved significantly more in HIIT, 18% and 23%, respectively, compared to CON, 8% and 12% (95% CI 3.9; 30.8 and 00:06; 03:18, respectively). Muscle biopsies (HIIT n = 7, CON n = 6) showed increases (p < 0.05) in central mitochondrial protein expression in HIIT but not CON, suggesting enhanced mitochondrial function. Both groups maintained stable serum muscle enzymes indicating no increase in disease activity from the intervention. Muscle disease activity remained low and unchanged in both groups (95% CI -1.2; 1.0), physician global activity and MMT8 significantly improved within CON (95% CI -1.7; -0.26 and 0.1; 3.9, respectively) but not in the HIIT group. INTERPRETATION: HIIT is an effective and safe exercise intervention to improve aerobic fitness, muscle endurance, and mitochondrial function in patients with recent onset IIM. This approach should be considered an adjuvant treatment in managing IIM, potentially health-enhancing for these patients. FUNDING: Swedish Research Council, the Swedish Rheumatism Association, Stockholm County Research Grant (ALF), King Gustaf V 80-year Foundation, the Swedish Heart and Lung Foundation, Promobilia Foundation, and Stig Thune Foundation.