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

Abstract

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 ~100 or ~125% [Formula: see text]. Change in [Formula: see text] was used to monitor protocol efficacy, while Actiheart™ 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 (~125% [Formula: see text]) used during a 5-by-1 min HIT protocol resulted in a robust increase in [Formula: see text] (136 participants, +10.0%, p < 0.001; large size effect). 5-by-1 HIT reduced MAP (~3%; p < 0.001) and HOMA-IR (~16%; p < 0.01). Physiological responses were similar in men and women while a sizeable proportion of the training-induced changes in [Formula: see text], 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 [Formula: see text], 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.

Keywords: [Formula: see text]; blood pressure; detraining; exercise; health; high-intensity interval training; homeostatic model assessment of insulin resistance; variability.

Figure 1

Flow chart of participant contact, screening, and retention through the phases of the study.

Figure 2

An analysis of the training response to 5-by-1 HIT for $\dot{\text{V}}{\text{O}}_2\text{\hspace{0.17em}max}$, MAP and HOMA-IR in men and women. Inter-participant variability in response to HIT is large for both men and women, but on average both genders respond to a similar extent. Abbreviations: $\dot{\text{V}}{\text{O}}_2\text{\hspace{0.17em}max}$, maximal aerobic capacity; MAP, mean arterial pressure; HOMA-IR, homeostatic model assessment of insulin resistance; HIT, high-intensity interval training.

Figure 3

Comparison of the inter-individual variability to exercise training contrasting short-term high-intensity training with longer-term high-volume submaximal training. The training response to 6-weeks 5-by-1 high-intensity interval training [(A,C,E); black bars] and our previously published 8-month STRRIDE AT and AT/RT exercise training study [(B,D,F); gray bars] for $\dot{\text{V}}{\text{O}}_2\text{\hspace{0.17em}max}$, MAP, and HOMA-IR. Training-induced changes in both ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$ (A,B), MAP (C,D), and HOMA-IR (E,F) vary considerably in both studies and to a similar extent. Abbreviations: AT, aerobic training; RT, resistance training; ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$, maximal aerobic capacity; MAP, mean arterial pressure; HOMA-IR, homeostatic model assessment of insulin resistance.

Figure 4

Presentation of the responder frequency for the three main clinical biomarkers considered in this study [high-intensity interval training (HIT)] and comparison with our previously published endurance training (ET) study. Each individual was assessed for improvement in $\dot{\text{V}}{\text{O}}_2\text{\hspace{0.17em}max}$, mean arterial pressure, or HOMA-IR, greater than the laboratory error, and the percentile frequency of 0, 1, 2, or 3 from three improvements was calculated. For sake of comparison, this is plotted side-by-side with the percentile frequency of 0, 1, 2, or 3 gains based on numerical improvements (a criteria that would be considered unreliable by most). Approximately 40% of subjects demonstrate improvement in only one health biomarker, while between 4 and 9% demonstrate no reliable improvement in any.

Figure 5

Presentation of the average retention of the training-induced changes observed 3 weeks after cessation of 5-by-1 high-intensity interval training. A value of 100% represents the training effect and a value of 0% indicates that the training effect is lost 3 weeks after training (under sedentary conditions). Significant differences from baseline: **p < 0.01, ***p < 0.001. Significant differences from post-training: ^{^^^}p < 0.001. Abbreviations: $\dot{\text{V}}{\text{O}}_2\text{\hspace{0.17em}max}$, maximal aerobic capacity; Wmax, maximal power output; SBP, systolic blood pressure; DBP, diastolic blood pressure; MAP, mean arterial pressure; HOMA-IR, homeostatic model assessment of insulin resistance.