AUTHOR=Sian Tanvir S. , Inns Thomas , Gates Amanda , Doleman Brett , Gharahdaghi Nima , Atherton Philip J. , Lund Jon N. , Phillips Bethan E. 

TITLE=Short-Term, Equipment-Free High Intensity Interval Training Elicits Significant Improvements in Cardiorespiratory Fitness Irrespective of Supervision in Early Adulthood

JOURNAL=Frontiers in Sports and Active Living

VOLUME=3

YEAR=2021

URL=https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2021.697518

DOI=10.3389/fspor.2021.697518

ISSN=2624-9367

ABSTRACT=<p><bold>Introduction:</bold> Serious health implications from having low levels of cardiorespiratory fitness (CRF) and being overweight in young adulthood are carried forward into later life. High-intensity interval training (HIIT) is a time-effective, potent stimulus for improving CRF and indices of cardiometabolic health. To date, few studies have investigated the use of equipment-free HIIT or the impact of supervision for improving CRF via HIIT.</p><p><bold>Methods:</bold> Thirty healthy young adults (18–30 y) were randomised to 4 weeks (12 sessions) equipment-free, bodyweight based supervised laboratory HIIT (L-HIIT), unsupervised home HIIT (H-HIIT) or no-intervention (CON). Utilised exercises were star jumps, squats and standing sprints. Measurements of CRF (anaerobic threshold (AT) and VO<sub>2</sub>peak), blood pressure (BP), body mass index (BMI), blood glucose and plasma insulin by oral glucose tolerance test (OGTT), and muscle architecture were performed at baseline and after the intervention.</p><p><bold>Results:</bold> When compared to the control group, both HIIT protocols improved CRF (AT: L-HIIT mean difference compared to the control group (MD) +2.1 (95% CI: 0.34–4.03) ml/kg/min; <italic>p</italic> = 0.02; H-HIIT MD +3.01 (1.17–4.85) ml/kg/min; <italic>p</italic> = 0.002), VO<sub>2</sub>peak: L-HIIT (MD +2.94 (0.64–5.25) ml/kg/min; <italic>p</italic> = 0.01; H-HIIT MD +2.55 (0.34–4.76) ml/kg/min; <italic>p</italic> = 0.03), BMI (L-HIIT MD −0.43 (−0.86 to 0.00) kg/m<sup>2</sup>; <italic>p</italic> = 0.05; H-HIIT: MD −0.51 (−0.95 to −0.07) kg/m<sup>2</sup>; <italic>p</italic> = 0.03) and <italic>m. vastus lateralis</italic> pennation angle (L-HIIT MD 0.2 (0.13–0.27)°; <italic>p</italic> &lt; 0.001; H-HIIT MD 0.17 (0.09 to 0.24)°; <italic>p</italic> &lt; 0.001). There was no significant change in BP, blood glucose or plasma insulin in any of the groups.</p><p><bold>Conclusions:</bold> Four weeks time-efficient, equipment-free, bodyweight-based HIIT is able to elicit improvements in CRF irrespective of supervision status. Unsupervised HIIT may be a useful tool for counteracting the rise of sedentary behaviours and consequent cardiometabolic disorders in young adults.</p>