Breast cancer survivors (BCS) undergoing chemotherapy (CT) show a significant increase in time engaged in sedentary behavior (SB); however, limited research exists on how SB affects common, negative CT side effects. This study used ecological momentary assessment and waist-worn accelerometers to examine the relationship between increased SB and subsequent momentary symptom ratings during CT.
BCS (N=67, Mage= 48.5±10.4 years) undergoing CT for early-stage BC wore an accelerometer on their hip during waking hours and completed symptom (affect, anxiety, depression, fatigue, pain, and cognitive functioning) rating surveys four times per day for ten consecutive days (3 days pre-, day of, and 6 days post-CT) at the beginning, middle, and last cycles of CT. Each minute of wear time was categorized as SB (yes/no). The number of minutes spent in SB in the 2 hours before each prompt was calculated. Variance was decomposed by calculating each person’s mean SB minutes during these pre-prompt periods (between-subject) and the difference between this person mean and the SB minutes before a given survey (within-subject).

Mixed models were used to examine the relationship between the between and within-person variation of SB minutes and the change in subsequent symptom ratings. Models controlled for cycle of CT, time of day, weekday, and CT day status. A total of 6765 of 7947 total surveys were answered (85.1%); 306 surveys (3.9%) did not have two hours of valid wear time preceding the survey and were removed from the analysis. Participants engaged in an average of 88.52 (SD=20.34) SB minutes in the two hours before a prompt. Engagement in 10 more minutes of SB than usual was significantly (p<.01) associated with increased odds of rating a worse mood (OR=1.11), worse cognitive function (OR=1.09) and greater depression (OR=1.05), fatigue (OR=1.12), and pain (OR=1.09). Engagement in 10 more minutes of SB compared to the average across all participants was significantly (p<.01) associated with increased odds of rating a worse mood (OR=2.79) and greater fatigue (OR=3.04).

Findings indicate that after engaging in more SB than average during CT, BCS reported worse ratings on all treatment-related side effects except for anxiety. Future research should develop and test SB reduction interventions during CT to examine how to reduce CT side effects effectively.