Distinct trajectories of physical activity and sedentary behavior

From the Greenlee Group, Division of Public Health Sciences

The majority of population-based surveys have reported that breast cancer survivors do not meet the recommended physical activity (PA) levels, which includes at least 150 minutes per week of moderate to vigorous physical activity (MVPA). MVPA has been shown to increase the long-term survival of cancer patients. The Greenlee group’s goal was to understand how women altered their PA after breast cancer diagnosis. Any emergent patterns could aid in survivors achieving the recommended PA levels. This study, published in the Journal of Cancer Survivorship, used methods designed to establish latent groups of longitudinal trajectories. These analyses are more applicable to distinguishing changes in PA after diagnoses. Group-based trajectory modeling (GBTM) is an analytical method that pinpoints developmental trajectory groups based on the shape parameters of the trajectory curve. There has only been one other study to utilize GBTM to identify changes in PA levels, and few studies have used GBTM to examine sedentary behavior and breast cancer survivors. 

The data from this study was acquired through the Pathways Study, which is a population-based prospective cohort of women (n= 4505) diagnosed with invasive breast cancer.  The women were enrolled at Kaiser Permanente Northern California (KPNC) from January 2006 to April 2013. Majority of the participants were recruited two months after diagnosis; the women had begun radiation therapy (34%), chemotherapy (46%), and/or hormonal therapy (40%). The data used for the Pathways Study was collected by completing the Arizona Activity Frequency Questionnaire.

The Greenlee group hypothesized observing five distinct PA trajectories after a breast cancer diagnoses which included consistency at baseline PA levels, a steady increase or decrease in PA, and a temporary increase or decrease in PA. The Greenlee group addressed research gaps by using GBTM to identify distinct trajectories of MVPA and sedentary behaviors for breast cancer survivors during the first 24 months after diagnosis. In addition, the group examined PA trajectories with respect to socioeconomic status, psychosocial factors, and cancer treatment side effects. The outcome variables were time spent on MVPA and sedentary behavior from baseline, six months, 24 months follow-up. The trajectory groups were classified by the level of baseline MVPA or sedentary behavior (high, medium, or low) and the direction of variable change (increaser, decreaser, or maintainer). 

Graphical representation of Distinct trajectories of physical activity and sedentary behavior
Distinct trajectories of physical activity and sedentary behavior Image from Dr. Zaixing Shi

According to Dr. Zaixing Shi, the first author of the publication, “The figure best describes the article. The lines represent the average amount of physical activity of our participants at various time points after cancer diagnosis.” Figure A shows time spent on moderate to vigorous intensity physical activity incudes high decreasers (7%), medium decreasers (35%) and low maintainers (58%). Figure B shows sedentary behavior, the four trajectories include high maintainers (18%), high decreasers (27%), low increasers (24%), and low maintainers (31%).  Dr. Shi elaborated on the results, “Our findings demonstrated that 42% of breast cancer survivors decreased moderate to vigorous PA and 73% maintained or increased sedentary time during the 24 months following diagnosis. Socioeconomic status and stress coping at diagnosis predicted subsequent PA trajectory.” 

Dr. Shi detailed future implications, “Although we now have better idea of how patients change PA after diagnosis, we still don’t know why they change. Research is needed to better understand the physical and mental barriers to maintaining regular physical activity among breast cancer survivors. Also, it would be interesting to look at more objective and quantitative PA data, such as those captured by a Fitbit.” It’s important for patients to receive education and counseling/ interventions on the impact of treatment on their daily activities and strategies to prevent decreases or lost in activities. Dr. Shi concluded, “This type of data can give us more hint of when patients start to change PA over the period from cancer treatment to recovery, and the actual amount of change. Finally, we are interested in comparing cancer outcomes among the different PA trajectories to evaluate the impact of PA change on breast cancer survival.”

This research was supported by NCI/NIH and the Land China Scholarship Council predoctoral training award.

Fred Hutch/UW Cancer Consortium member Heather Greenlee

Shi Z, Rundle A, Genkinger JM, Cheung YK, Ergas IJ, Roh JM, Kushi LH, Kwan ML, Greenlee H. Distinct trajectories of moderate to vigorous physical activity and sedentary behavior following a breast cancer diagnosis: the Pathways Study. Journal of Cancer Survivorship. 2020 Mar 4:1-1. https://doi.org/10.1007/s11764-020-00856-0