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% ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$. Change in ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$ 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% ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$) used during a 5-by-1 min HIT protocol resulted in a robust increase in ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$ (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 ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$, 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 ${\dot{\text{V}}\text{O}}_{\text{2}}\text{\hspace{0.17em}max}$, 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.

AMP-activated protein kinase (AMPK) is a major mediator of the exercise response and a molecular target to improve insulin sensitivity. To determine if the anaerobic component of the exercise response, which is exaggerated when sprint is performed in severe acute hypoxia, influences sprint exercise-elicited Thr¹⁷²-AMPKα phosphorylation, 10 volunteers performed a single 30-s sprint (Wingate test) in normoxia and in severe acute hypoxia (inspired Po₂: 75 mmHg). Vastus lateralis muscle biopsies were obtained before and immediately after 30 and 120 min postsprint. Mean power output and O₂ consumption were 6% and 37%, respectively, lower in hypoxia than in normoxia. O₂ deficit and muscle lactate accumulation were greater in hypoxia than in normoxia. Carbonylated skeletal muscle and plasma proteins were increased after the sprint in hypoxia. Thr¹⁷²-AMPKα phosphorylation was increased by 3.1-fold 30 min after the sprint in normoxia. This effect was prevented by hypoxia. The NAD⁺-to-NADH.H⁺ ratio was reduced (by 24-fold) after the sprints, with a greater reduction in hypoxia than in normoxia ( P < 0.05), concomitant with 53% lower sirtuin 1 (SIRT1) protein levels after the sprint in hypoxia ( P < 0.05). This could have led to lower liver kinase B1 (LKB1) activation by SIRT1 and, hence, blunted Thr¹⁷²-AMPKα phosphorylation. Ser⁴⁸⁵-AMPKα₁/Ser⁴⁹¹-AMPKα₂ phosphorylation, a known negative regulating mechanism of Thr¹⁷²-AMPKα phosphorylation, was increased by 60% immediately after the sprint in hypoxia, coincident with increased Thr³⁰⁸-Akt phosphorylation. Collectively, our results indicate that the signaling response to sprint exercise in human skeletal muscle is altered in severe acute hypoxia, which abrogated Thr¹⁷²-AMPKα phosphorylation, likely due to lower LKB1 activation by SIRT1.