A Practical and Time-Efficient High-Intensity Interval Training Program Modifies Cardio-Metabolic Risk Factors in Adults with Risk Factors for Type II Diabetes.

Introduction: Regular physical activity (PA) can reduce the risk of developing type 2 diabetes, but adherence to time-orientated (150 min week-1 or more) PA guidelines is very poor. A practical and time-efficient PA regime that was equally efficacious at controlling risk factors for cardio-metabolic disease is one solution to this problem. Herein, we evaluate a new time-efficient and genuinely practical high-intensity interval training (HIT) protocol in men and women with pre-existing risk factors for type 2 diabetes. Materials and methods: One hundred eighty-nine sedentary women (n = 101) and men ( n = 88) with impaired glucose tolerance and/or a body mass index >27 kg m(-2) [mean (range) age: 36 (18-53) years] participated in this multi-center study. Each completed a fully supervised 6-week HIT protocol at work-loads equivalent to similar to 100 or similar to 125% VO2 max. Change in VO2 max was used to monitor protocol efficacy, while Actiheart(TM) monitors were used to determine PA during four, weeklong, periods. Mean arterial (blood) pressure (MAP) and fasting insulin resistance [homeostatic model assessment (HOMA)-IR]represent key health biomarker outcomes. Results: The higher intensity bouts (similar to 125% VO2 max) used during a 5-by-1 min HIT protocol resulted in a robust increase in VO2 max (136 participants, + 10.0%, p < 0.001; large size effect). 5-by-1 HIT reduced MAP (similar to 3%; p < 0.001) and HOMA-IR (similar to 16%; p < 0.01). Physiological responses were similar in men and women while a sizeable proportion of the training-induced changes in VO2 max, MAP, and HOMA-IR was retained 3 weeks after cessation of training. The supervised HIT sessions accounted for the entire quantifiable increase in PA, and this equated to 400 metabolic equivalent (MET) min week-1. Meta-analysis indicated that 5-by-1 HIT matched the efficacy and variability of a time-consuming 30-week PA program on VO2 max, MAP, and HOMA-IR. Conclusion: With a total time-commitment of < 15 min per session and reliance on a practical ergometer protocol, 5-by-1 HIT offers a new solution to modulate cardio-metabolic risk factors in adults with pre- existing risk factors for type 2 diabetes while approximately meeting the MET min week-1 PA guidelines. Long-term randomized controlled studies will be required to quantify the ability for 5-by-1 HIT to reduce the incidence of type 2 diabetes, while strategies are required to harmonize the adaptations to exercise across individuals.