Dynamic activity – fatigue relationships in daily life in ME/CFS: insights from ecological momentary assessment

Abstract

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating condition characterized by persistent fatigue and post-exertional malaise (PEM), in which even minimal exertion can lead to a worsening of symptoms. Fatigue levels in ME/CFS are highly variable and fluctuate unpredictably in daily life. However, studies investigating symptom fluctuations in real-time remain scarce. The goal of this study was to examine inter-individual differences in the relationship between daily activities and fatigue in individuals with ME/CFS using ecological momentary assessment (EMA). Methods: One hundred nine individuals with ME/CFS and 55 healthy controls (HC) completed a seven-days experience sampling protocol, receiving eight semi-random prompts per day. At each prompt, participants reported momentary physical fatigue levels, whether they had just engaged in physical activity (yes/no), and how much they enjoyed their current activity. Random-intercept, random-slope linear mixed models were used to compare concurrent and lagged (i.e. 2 prompts or 3-4h later) activity-fatigue relationships between groups, and to derive individual slopes as indices of activity-triggered fatigue. In ME/CFS, we examined correlations between individual activity-fatigue slopes and a lab-based measure of PEM (4h recovery after cycling task). Results: In all models, individuals with ME/CFS had higher levels of self-reported momentary fatigue than HC (p < 0.001), despite no case-control differences in the proportion of “active” prompts (HC: 47.0%; ME/CFS: 44.2%, p = 0.43). Overall, active prompts were associated with higher concurrent (p < 0.001) and lagged (p = 0.006) fatigue levels, but this was the case for both ME/CFS and HC (activity x group interactions: p = 0.25, 0.35 resp.). However, activity enjoyment was significantly negatively associated with concurrent fatigue severity in ME/CFS but positively associated in HC (enjoyment x group interaction: p < 0.001; Figure 1). Within the ME/CFS group, lab-based PEM was unrelated to EMA-based individual activity-fatigue slopes (concurrent: p = 0.12, lagged: p = 0.95). Conclusion: Individuals with ME/CFS reported elevated fatigue even in the absence of activity, while activity-triggered increases were comparable to HC. Enjoyment of activities uniquely buffered fatigue in ME/CFS, highlighting the importance of considering contextual factors. Individual slopes derived from EMA are a promising measure of PEM in daily life, although sensitivity was limited by assessing only whether participants were active immediately before the prompt, leading to zero-inflation and preventing investigation of how activity intensity relates to fatigue in ME/CFS.