Short-term, equipment-free high intensity interval training elicits significant improvements in the cardiorespiratory fitness of young adults irrespective of supervision

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[less than]0.001; H-HIIT MD 0.17 (0.09 to 0.24)º; p[less than]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 ais 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.