The time course of the therapeutic influence of a single exercise bout on cancer-related fatigue

Abstract

Introduction: Cancer-related fatigue (CRF) is a critical outcome for cancer survivors due to its high prevalence, impact on activities of daily living (ADLs), and quality of life (QOL). Non-pharmacological interventions, such as chronic exercise interventions, are a promising intervention target to improve CRF. However, the effect of these interventions is often only studied at the baseline and post-intervention period; therefore, it does not capture the dynamic nature of how CRF may change daily and even weekly within those intervention periods. Studying these within-day and weekly changes may have important implications on exercise motivation, especially when cancer survivors are experiencing severe CRF. Exploring these effects may lead to improved long-term exercise adherence in cancer survivors. To fill in the gap of how exercise affects CRF daily during a 12-week exercise program, additional research must be conducted to explore the acute effects of exercise on CRF and how factors such as exercise intensity may have a role in the impact of change. Therefore, the purpose of this dissertation is to (1) examine changes in CRF from immediately before to immediately after exercise sessions during an exercise program for cancer survivors, (2) changes in CRF up to 7-hours following a single-bout of exercise on an exercise and non-exercise day, and (3) how self-selected exercise intensity impacts CRF immediately following, and after up to 7-hours after an exercise session. Methods: An observational, longitudinal cohort study of (n=25) cancer survivors was conducted to study within-day trends of CRF. Participants (for all studies) completed a 12-week exercise program in an outpatient cancer rehabilitation program. Exercise classes were held twice per week, and participants were assigned to a set day and time. CRF was assessed using a visual analog scale (0=no fatigue–10=worst fatigue), before, and immediately after exercise; and 1-, 4-, & 7- hours following one exercise class per week and at the same times the following day on one non-exercise day per week via a phone application, ExpiWell. Finally, heart rate and rate of perceived exertion were collected once a week to capture participants' self-selected exercise intensity for each given session. Demographics were calculated using mean ± standard deviation or frequencies (%). Mixed effects models with random and fixed effects were used to evaluate CRF immediately after exercise and over the course of the day. Statistical significance for all studies was set at p<.05. Results: This work examined changes in CRF from immediately before to immediately after exercise sessions. Overall, it did not demonstrate acute effects of exercise on CRF, and there was no difference in the magnitude of CRF change from week to week. When assessing CRF at hour 1-, 4 and 7-hours post exercise, findings revealed that on exercise days, CRF demonstrated a positive significant slope for CRF from immediately post-exercise through 1, -4, and -7 hours, with CRF levels remaining stable at 1- and 4-hours compared to post exercise before rising significantly by the 7-hour timepoint compared to post-exercise. On non-exercise days, CRF demonstrated a positive significant slope for CRF from the 1-hour timepoint through 4, and -7 hours; however, CRF levels at each timepoint (4 and 7 hours) were not significantly different than the 1-hour timepoint. Notably, comparisons between exercise and non-exercise days revealed no significant differences in CRF slopes, suggesting that CRF tends to follow a similar trend during the day, independent of exercising. Conclusion: CRF did not significantly decrease following a single session of exercise, nor did categorizing exercise sessions by intensity level reveal differences in CRF outcomes. Across the course of the exercise day, CRF gradually increased, peaking at hour 7. Interestingly, this pattern was also observed on non-exercise days. However, the reported CRF remained below a moderate threshold, suggesting that while exercise did not alleviate CRF, it also did not lead to a statistically significant increase in CRF during or after the sessions. The findings presented in this dissertation offer a vital perspective on the acute effects of a single bout of exercise on CRF. Future research should conduct randomized controlled trials that will aim to establish a causal relationship between exercise and immediate reductions in CRF, while allowing for consideration of several key CRF moderators. In addition, future studies should include the collection of biomarkers that examine the underlying physiologic mechanisms of the change in CRF immediately following a bout of exercise and over the course of a day.