A comparison of high versus low dose of exercise training in exercise-based cardiac rehabilitation: a randomized controlled trial with 12-months follow-up

Abstract

Objective: To assess if a higher dose of exercise training in exercise-based cardiac rehabilitation could affect improvements in aerobic capacity and muscle strength.

Design: Assessor-blinded randomized controlled trial with 12-months follow-up.

Setting: Aarhus University Hospital, Aarhus, Denmark.

Subjects: A total of 164 cardiac patients referred to exercise-based cardiac rehabilitation were recruited.

Interventions: Patients were randomized to 1-hour exercise sessions either three times weekly for 12 weeks (36 sessions, high-dose group) or twice weekly for 8 weeks (16 sessions, low-dose group). The same standardized exercise and intensity protocol including aerobic and muscle strength training was used in all participants.

Main measures: Primary outcome was changes in VO_2peak. Secondary outcomes were changes in maximal workload, muscle strength and power. Measures were obtained at baseline, after termination of the rehabilitation programme and at follow-up after 6 and 12 months.

Results: After the end of intervention, statistically significant between-group differences were seen in favour of the high-dose group in all outcomes: VO_2peak 2.6 (mL kg^-1 min^-1) (95% confidence interval (CI): 0.4-4.8), maximal workload 0.3 W kg^-1 (95%CI: 0.02-0.5), isometric muscle strength 0.7 N m kg^-1 (95%CI: 0.1-1.2) and muscle power 0.3 W kg^-1 (95%CI: 0.04-0.6). After 12 months, a significant between-group difference only persisted in VO_2peak and maximal workload.

Conclusion: A higher dose of exercise training had a small effect on all outcomes at termination of intervention. A long-term effect persisted in VO_2peak and maximal workload. Although the effect was small, it is an important finding because VO_2peak is the most important predictor of all-cause mortality in cardiac patients.

Keywords: Cardiac rehabilitation; dose response; exercise training; physical capacity; randomized controlled trial.