Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA159

Poster Communications

Four-weeks equipment-free high-intensity interval training does not improve the cardiorespiratory fitness of young healthy adults, but does elicit gains in muscle mass

T. S. Sian1,2, T. Inns1, J. E. Blackwell1,2, J. N. Lund1,2, B. E. Phillips1

1. MRC-ARUK Centre for Musculoskeletal Ageing Research, University of Nottingham, Derby, United Kingdom. 2. Division of Surgery and Anaesthetics, Royal Derby Hospital, Derby, United Kingdom.

Introduction: Low cardiorespiratory fitness (CRF) and skeletal muscle mass (MM) are both associated with increased morbidity and mortality (1). Despite exercise training being a proven method to improve both CRF and MM, a strikingly low proportion (2) of UK adults meet the current government guidelines for exercise (3), with "lack of time" one of the most-commonly cited barriers (4). One exercise training mode that has been proven to improve CRF with a reduced time-commitment is high-intensity interval training (HIIT) (5). However, the majority of HIIT research has involved training on a specialised cycle ergometer with intensity determined by a pre-training cardiopulmonary exercise test (CPET). In order to assess the efficacy of HIIT with a further barrier to exercise (equipment) removed, we investigated the efficacy of 4-weeks equipment-free HIIT for improving CRF and MM in young adults. Methods: Eight healthy volunteers aged 25 (18-35) y, were randomised to HIIT or a no-intervention control group. For the HIIT group, exercise sessions comprised a brief warm-up, five 1-minute bouts of high-intensity, equipment-free efforts (star-jumps, squats and static sprints) interspersed with 90-seconds recovery and a final recovery period. Each session lasted 15-minutes, with all volunteers completing 12 sessions over 4-weeks. CRF was assessed before and after the intervention by CPET, with muscle (vastus lateralis (VL)) thickness assessed by ultrasound. Results: HIIT did not elicit significant increases in either of our measures of CRF (AT: anaerobic threshold (13.7±2.0 vs. 15.7±2.7 ml/kg/min, P=0.09); or VO2 max (32.6±7.6 vs. 33.4±7.6 ml/kg/min, P=0.6113)), with no change in either of these parameters in the control group (AT: 19.6±7.9 vs. 19.9±9.2 ml/kg/min, P=0.9; VO2 max: 40.7±12.2 vs. 40.6±13.7 ml/kg/min, P=0.9). Despite these findings, 75% of volunteers in the HIIT group did achieve an increase in AT above the threshold previously stated as clinically meaningful (>1.5 ml/kg/min). HIIT did elicit significant increases in VL muscle thickness (218.8±4.5 vs. 226.5±4.5 mm, P=0.04), with no change observed in the control group (246.3±6.0 vs. 247.3±7.4 mm, P=0.9). Discussion: Despite our time-efficient, equipment-free HIIT programme not being able to elicit significant improvements in CRF in this study, the trend towards an increase in AT and the significant increase in muscle thickness, suggest that this format of HIIT can be beneficial in improving physiological parameters associated with fitness and well-being. As the majority of individuals in the HIIT group did make meaningful gains in AT, further research in a larger cohort is required to assess the true utility of this intervention for improving CRF, and to determine the heterogeneity of adaptation to this mode of exercise.

Where applicable, experiments conform with Society ethical requirements