Reallocating sedentary time to physical activity: effects on fatigue and quality of life in patients with breast cancer in the Phys-Can project

PURPOSE: We aimed to investigate the effects of reallocating sedentary time to an equal amount of light (LPA) or moderate-to-vigorous intensity physical activity (MVPA) on cancer-related fatigue and health-related quality of life (HRQoL) in patients with breast cancer. We also aimed to determine the daily amount of sedentary time needed to be reallocated to LPA or MVPA to produce minimal clinically important changes in these outcomes. METHODS: Pooled baseline data from three studies were used, including women with breast cancer who participated in the Phys-Can project. Fatigue was assessed with the Multidimensional Fatigue Inventory questionnaire (MFI; five dimensions, 4–20 scale) and HRQoL with the European Organisation for Research and Treatment of Cancer quality of life questionnaire (EORTC QLQ-C30; 0–100 scale). Sedentary time and physical activity were measured with accelerometry. Isotemporal substitution modelling was used for the analyses. RESULTS: Overall, 436 participants (mean age 56 years, fatigue 11 [MFI], HRQoL 66 [EORTC QLQ-C30], LPA 254 min/day, MVPA 71 min/day) were included. Fatigue significantly decreased in two MFI dimensions when reallocating 30 min/day of sedentary time to LPA: reduced motivation and reduced activity (β = − 0.21). Fatigue significantly decreased in three MFI dimensions when reallocating 30 min/day of sedentary time to MVPA: general fatigue (β = − 0.34), physical fatigue (β = − 0.47) and reduced activity (β = − 0.48). To produce minimal clinically important changes in fatigue (− 2 points on MFI), the amount of sedentary time needed to be reallocated to LPA was ≈290 min/day and to MVPA was ≥ 125 min/day. No significant effects were observed on HRQoL when reallocating sedentary time to LPA or MVPA. CONCLUSIONS: Our results suggest that reallocating sedentary time to LPA or MVPA has beneficial effects on cancer-related fatigue in patients with breast cancer, with MVPA having the greatest impact. In relatively healthy and physically active breast cancer populations, a large amount of time reallocation is needed to produce clinically important changes. Future studies are warranted to evaluate such effects in broader cancer populations. Trial registration: NCT02473003 (10/10/2014) and NCT04586517 (14/10/2020).