Exercise training is a clinically proven, cost-effective, primary intervention that delays and in many cases prevents the health burdens associated with many chronic diseases. However, the precise type and dose of exercise needed to accrue health benefits is a contentious issue with no clear consensus recommendations for the prevention of inactivity-related disorders and chronic diseases. A growing body of evidence demonstrates that high-intensity interval training (HIT)canserveasaneffectivealternatetotraditionalendurance-basedtraining,inducingsimilar or even superior physiological adaptations in healthy individuals and diseased populations, at least when compared on a matched-work basis. While less well studied, low-volume HIT can also stimulate physiological remodelling comparable to moderate-intensity continuous training despite a substantially lower time commitment and reduced total exercise volume. Such findings areimportantgiventhat'lackoftime'remainsthemostcommonlycitedbarriertoregularexercise participation. Here we review some of the mechanisms responsible for improved skeletal muscle metabolic control and changes in cardiovascular function in response to low-volume HIT. We also consider the limited evidence regarding the potential application of HIT to people with, or at risk for, cardiometabolic disorders including type 2 diabetes. Finally, we provide insight on the utility of low-volume HIT for improving performance in athletes and highlight suggestions for future research.

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Physiological adaptations to low-volume, high-intensity interval training in health and disease

Low-volume ‘sprint’ interval training (SIT) stimulates rapid improvements in muscle oxidative capacity that are comparable to levels reached following traditional endurance training (ET) but no study has examined metabolic adaptations during exercise after these different training strategies. We hypothesized that SIT and ET would induce similar adaptations in markers of skeletal muscle carbohydrate (CHO) and lipid metabolism and metabolic control during exercise despite large differences in training volume and time commitment. Active but untrained subjects (23 ± 1 years) performed a constant-load cycling challenge (1 h at 65% of peak oxygen uptake ( ˙ VO2peak) before and after 6 weeks of either SIT or ET (n = 5 men and 5 women per group). SIT consisted of four to six repeats of a 30 s ‘all out’ Wingate Test (mean power output ∼500 W) with 4.5 min recovery between repeats, 3 days per week. ET consisted of 40‐60 min of continuous cycling at a workload that elicited ∼65% ˙ VO2peak (mean power output ∼150 W) per day, 5 days per week. Weekly time commitment (∼1.5 versus ∼4.5 h) and total training volume (∼225 versus ∼2250 kJ week −1 ) were substantially lower in SIT versus ET. Despite these differences, both protocols induced similar increases (P < 0.05) in mitochondrial markers for skeletal muscle CHO (pyruvate dehydrogenase E1α protein content) and lipid oxidation (3-hydroxyacyl CoA dehydrogenase maximal activity) and protein content of peroxisome proliferator-activated receptor-γ coactivator-1α. Glycogen and phosphocreatine utilization during exercise were reduced after training, and calculated rates of whole-body CHO and lipid oxidation were decreased and increased, respectively, with no differences between groups (all main effects, P < 0.05). Given the markedly lower training volume in the SIT group, these data suggest that high-intensity interval training is a time-efficient strategy to increase skeletal muscle oxidative capacity and induce specific metabolic adaptations during exercise that are comparable to traditional ET.

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Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans

Brief, intense exercise training may induce metabolic and performance adaptations comparable to traditional endurance training. However, no study has directly compared these diverse training strategies in a standardized manner. We therefore examined changes in exercise capacity and molecular and cellular adaptations in skeletal muscle after low volume sprint-interval training (SIT) and high volume endurance training (ET). Sixteen active men (21 +/- 1 years, ) were assigned to a SIT or ET group (n = 8 each) and performed six training sessions over 14 days. Each session consisted of either four to six repeats of 30 s 'all out' cycling at approximately 250% with 4 min recovery (SIT) or 90-120 min continuous cycling at approximately 65% (ET). Training time commitment over 2 weeks was approximately 2.5 h for SIT and approximately 10.5 h for ET, and total training volume was approximately 90% lower for SIT versus ET ( approximately 630 versus approximately 6500 kJ). Training decreased the time required to complete 50 and 750 kJ cycling time trials, with no difference between groups (main effects, P </= 0.05). Biopsy samples obtained before and after training revealed similar increases in muscle oxidative capacity, as reflected by the maximal activity of cytochrome c oxidase (COX) and COX subunits II and IV protein content (main effects, P </= 0.05), but COX II and IV mRNAs were unchanged. Training-induced increases in muscle buffering capacity and glycogen content were also similar between groups (main effects, P </= 0.05). Given the large difference in training volume, these data demonstrate that SIT is a time-efficient strategy to induce rapid adaptations in skeletal muscle and exercise performance that are comparable to ET in young active men.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.2006.112094

Short‐term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance

Technical performance during soccer matches of the Italian Serie A league: effect of fatigue and competitive level.

High-intensity interval training (HIT) is a potent time-efficient strategy to induce numerous metabolic adaptations usually associated with traditional endurance training. As little as six sessions of HIT over 2 wk or a total of only approximately 15 min of very intense exercise (approximately 600 kJ), can increase skeletal muscle oxidative capacity and endurance performance and alter metabolic control during aerobic-based exercise.

Metabolic adaptations to short-term high-intensity interval training: a little pain for a lot of gain?

Parra et al. (Acta Physiol. Scand 169: 157–165, 2000) showed that 2 wk of daily sprint interval training (SIT) increased citrate synthase (CS) maximal activity but did not change “anaerobic” work c...

https://www.physiology.org/doi/pdf/10.1152/japplphysiol.01095.2004

Suzanne N. Bradwell

Papers

Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans