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=Volume 3 - 2021

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=Introduction:
Serious health implications from having low levels of cardiorespiratory fitness (CRF) and/or 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. 
Methods:
Thirty healthy young adults (18-30 y) were randomised to 4 weeks equipment-free supervised HIIT (L-HIIT), unsupervised HIIT (H-HIIT) or no-intervention (CON). Measurements of CRF (anaerobic threshold (AT) and VO2peak (VO2)), blood pressure (BP), body mass index (BMI), blood glucose, plasma insulin and muscle architecture were performed at baseline and after the intervention.
Results:
Both HIIT protocols improved CRF (AT: L-HIIT mean difference (MD) +2.1 (95% CI: 0.34 to 4.03) ml/kg/min; p=0.02; H-HIIT MD +3.01 (1.17 to 4.85) ml/kg/min; p=0.002), VO2: L-HIIT MD +2.94 (0.64 to 5.25) ml/kg/min; p=0.01; H-HIIT MD +2.55 (0.34 to 4.76) ml/kg/min; p=0.03), BMI (L-HIIT MD 0.18 (-0.35 to 0.5) kg/m2; p=0.04; H-HIIT: MD 0.19 (-0.25 to 0.63) kg/m2; p=0.03) and m. vastus lateralis pennation angle (L-HIIT MD 0.2 (0.13 to 0.27)º; p<0.001; H-HIIT MD 0.17 (0.09 to 0.24)º; p<0.001). There was no significant change in BP, glucose or insulin in any of the groups.
Conclusions:
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.