Safety of High-Intensity, Low-Volume Interval Training or Continuous Aerobic Training in Adults With Metabolic Syndrome

OBJECTIVE: The aim of the study was to evaluate the safety of high-intensity, low-volume interval training (HIIT-low volume) compared with moderate-intensity continuous aerobic training (MICT) in adults with metabolic syndrome. METHODS: This is a controlled, randomized, clinical trial in patients without history of ischemic heart disease or diabetes, who underwent a supervised, 3 sessions/week, 12-week treadmill exercise program. The HIIT-low volume (n = 29) sessions consisted of 6 intervals with 1-minute, high-intensity phases at 90% of peak oxygen consumption (VO2peak). The MICT (n = 31) trained at 60% of VO2peak for 30 minutes. A new approach to record and classify all clinical events according to possible causality based on Naranjo's algorithm was developed. RESULTS: Patients were 50.8 ± 6.0 years old, 70% women, with body mass index of 30.6 ± 4.0 kg/m2 and VO2peak of 29.0 ± 6.3 mL·kg-1·min-1. In total, 60 clinical events were recorded in the HIIT-low volume group and 48 in the MICT group, with 59.3% classified as general disease. Only 21 events were classified as adverse reactions possibly related to exercise, without any serious adverse reactions. Both interventions had a similar incidence of musculoskeletal events (incidence rate ratio, 1.1; 95% confidence interval, 0.6-1.8), but HIIT-low volume had a higher incidence of cardiovascular events (incidence rate ratio, 2.9; 95% CI, 0.4-22.8) after adjusting for age, sex, and body mass index (HIIT-low volume: chest pain [n = 1] and symptoms of venous insufficiency of lower limbs [n = 2]; MICT: chest pain [n = 1]). CONCLUSIONS: The HIIT-low volume and MICT are safe in patients with metabolic syndrome. We recommend a muscle-conditioning program prior to both and to avoid HIIT-low volume in treadmill in patients with venous insufficiency of the lower limbs.Trial registration number NCT03087721.