Discussion
fatigue, ’, breast cancer, cancer, lower cancer-related fatigue
CANCER, BREAST CANCER
In the present study, we investigated MVPA in cancer survivors who previously participated in an exercise intervention during curative cancer treatment. The aims were to assess the associations of (1) MVPA level at 12-months follow-up and (2) long-term MVPA patterns (from immediately post-intervention to 12-month follow-up) with different cancer-related health outcomes. We found that a daily increase of 30 minutes MVPA at 12-month follow-up was significantly associated with lower cancer-related fatigue, higher cardiorespiratory fitness, and less sedentary time at 12-month follow-up. Additionally, participants who had high MVPA levels immediately post-intervention and increased their MVPA levels at 12-month follow-up were those who had the greatest health benefits in terms of lower fatigue, higher HRQoL and less sedentary time.As hypothesized, both higher MVPA level at 12-month follow-up and increased long-term MVPA patterns, were significantly associated with improved cancer-related health outcomes. However, some differences between the 2 physical activity measures regarding the observed associations are worth noting. For example, both MVPA level at 12-month follow-up and long-term MVPA patterns were significantly associated with lower fatigue, but it is the most physically active participants (those in the “High & Increasing” category) who reported clinically relevant lower scores in physical fatigue compared to the least physically active participants (those in the “Low & Decreasing” category), as the difference in score exceeded the minimal clinically importance of 2 points.Results regarding sedentary time indicate that both MVPA level at 12-month follow-up and long-term MVPA patterns were significantly and negatively associated with this outcome. Notably, compared to the category with the least physically active participants (those in the “Low & Decreasing” category), all the other categories were superior suggesting that high and/or increased MVPA levels after the end of an exercise intervention may reduce time spent sedentary in cancer survivors. This is in line with an RCT where breast cancer survivors randomized to a 12-week of MVPA both significantly increased MVPA and reduced sedentary time compared with the control group.In general, participants in the “High & Increasing” category was superior to the other groups for most cancer-related health outcomes. These results suggest that having high MVPA levels immediately post-intervention and increasing these levels during the follow-up period may be optimal for health outcomes in the long term in cancer survivors. These results also reinforce a possible dose-response relationship between MVPA levels and different cancer-related health outcomes and support advice within existing international physical activity guidelines that exceeding recommended physical activity levels is likely to provide additional health benefits in cancer survivors.There are numerous strengths in this study. First, we extend current knowledge through (1) demonstrating the potential long-term benefits of increasing MVPA levels post-intervention for different cancer-related health outcomes and (2) providing evidence of such associations when physical activity levels are objectively assessed. Further, our findings add to the growing evidence that a dose-response relationship between MVPA levels and health benefits in cancer survivors exists. Strengths in this study also include a large sample, the longitudinal design and long-term follow-up. However, our study is not without limitations including the large number of participants lost to follow-up and the homogeneous study sample (ie, mainly women with breast cancer, highly educated and physically active when entering the study), limiting the generalizability of our results. Additionally, although our study design does not allow to determine the direction of causality, adjusting for several confounders and examining both MVPA levels at 12-month follow-up and long-term MVPA patterns strengthens our conclusions about the observed associations. Our multidimensional approach, combining absolute levels of physical activity (ie, MVPA level) with a relative measure of physical activity (ie, long-term MVPA patterns) also provides an accurate and well-rounded picture of cancer survivors’ long-term physical activity status.