The relationship between exercise dose and health-related quality of life with a phase III cardiac rehabilitation program

Purpose: To quantify the relationship between the change in exercise dose and health-related quality of life (HRQoL) in a cohort of patients participating in a community-based phase-3 cardiac rehabilitation (CR) program. Methods: A retrospective, pre-experimental (no control group) design of 58 participants that completed a phase-3, 12-week exercise-based CR program was used to test the current hypothesis. Self-reported HRQoL (36-Item Short Form Health Survey Version 2, SF-36v2) was assessed prior and after completing the CR program. The change in exercise dose was estimated from the assigned training load in weeks 1 and 12 of the CR program. A series of regression models were fitted to ascertain the relationship between the change in exercise dose and changes in the SF-36v2. Results: There was a strong quadratic trend between the change in exercise dose and the mean change in SF-36 Mental and Physical Health Summary Scores. Analysis of covariance showed that the mean changes in the SF-36 Summary Scores statistically fluctuate across quartiles of exercise dose. The data show that there is a threshold amount of increase in exercise (Q₂; 350–510 kcal week^{− 1}) needed to HRQoL and that greater amounts of exercise dose (Q₃; 511–687 and Q₄ ≥ 688 kcal week^{− 1}) did not improve HRQoL further. Conclusions: The current findings suggest that physical and mental health-related quality of life are improved with a phase-3 CR program. The dose–response relationship observed indicates that a threshold exercise dose is required to improve HRQoL, and that larger doses of exercise do not confer further improvements in HRQoL.