HIIT at Home: Enhancing Cardiorespiratory Fitness in Older Adults – A Randomised Controlled Trial

Background: This study aimed to investigate the effectiveness of a six-month home-based high-intensity interval training (HIIT) intervention to improve peak oxygen consumption (V̇O2peak) and lactate threshold (LT) in older adults.Methods: 233 healthy older adults (60-84 years; 54% females) were randomly assigned to either six-month, thrice-weekly home-based HIIT (once-weekly circuit training and twice-weekly interval training) or a passive control group. Exercise sessions were monitored using a Polar watch and a logbook for objective and subjective data, respectively, and guided by a personal coach. The outcomes were assessed using a modified Balke protocol combining V̇O2peak and LT measures.1 General linear regression models assessed between-group differences in change and within-group changes for each outcome.Results: There was a significant between-group difference in the pre-to-post change in V̇O2peak (difference: 1.8 [1.2;2.3] mL/kg/min; exercise: +1.4 [1.0;1.7] mL/kg/min; control: -0.4 [-0.8;-0.0] mL/kg/min; effect size (ES):0.35). Compared to controls, the exercise group had lower blood lactate concentration (-0.7 [-0.9;-0.4] mmol/L, ES:0.61), % of peak heart rate (-4.4 [-5.7;-3.0], ES:0.64), and % of V̇O2peak (-4.5 [-6.1;-2.9], ES:0.60) at the intensity corresponding to pre-intervention LT, and achieved a higher treadmill stage at LT (0.6 [0.3;0.8]; ES:0.47), following the intervention. Conclusion: This study highlights the effectiveness of a home-based HIIT intervention as an accessible and equipment-minimal strategy to induce clinically meaningful improvements in cardiorespiratory fitness in older adults. Over six months, the exercise group showed larger improvements in all outcomes compared to the control group. Notably, the LT outcome exhibited a more pronounced magnitude of change than V̇O2peak.