Physical activity measures in patients with myalgic encephalomyelitis/chronic fatigue syndrome: correlations between peak oxygen consumption, the physical functioning scale of the SF-36 questionnaire, and the number of steps from an activity meter. — CFSMEATLAS
Physical activity measures in patients with myalgic encephalomyelitis/chronic fatigue syndrome: correlations between peak oxygen consumption, the physical functioning scale of the SF-36 questionnaire, and the number of steps from an activity meter.
van Campen, C M C, Rowe, Peter C, Verheugt, Freek W A et al. · Journal of translational medicine · 2020 · DOI
Quick Summary
This study compared three different ways to measure physical activity in ME/CFS patients: a questionnaire about daily functioning, a step counter worn during normal activities, and a fitness test measuring oxygen use during exercise. All three methods showed similar patterns—patients with lower scores on one test also tended to have lower scores on the others—but individual patients showed wide variations between the different measurements.
Why It Matters
ME/CFS lacks consensus on how to best measure physical decline and treatment response. This study validates that multiple assessment methods (questionnaires, activity monitors, and exercise testing) capture related but complementary information, supporting a more comprehensive approach to evaluating disease severity and monitoring changes over time in clinical and research settings.
Observed Findings
All three measures (PFS questionnaire, daily steps, and peak VO₂) were significantly and positively correlated in 99 female ME/CFS patients (P < 0.001 for all comparisons).
Correlations between measures remained consistent in patients with and without fibromyalgia comorbidity.
Correlations remained consistent regardless of whether patients achieved maximal exercise effort on stress testing (RER ≥ 1.1).
When 20 patients were re-evaluated for symptom worsening, all three measures showed significant declines (P < 0.0001).
Despite strong group-level correlations, individual patients showed large variation in relative scores across the three measures.
Inferred Conclusions
The three measurement modalities (questionnaire, activity monitor, and exercise test) assess related aspects of physical functioning and can be used together to reinforce findings.
Using only one type of measurement is insufficient for ME/CFS assessment; multi-modal measurement can reveal clinically important discrepancies in individual patients.
A comprehensive assessment integrating questionnaires, activity monitoring, and objective exercise testing may improve detection of treatment response and disease progression.
Remaining Questions
Which specific combinations of the three measures best predict clinical outcomes or treatment response in ME/CFS?
What This Study Does Not Prove
This study does not establish causation or explain why individual patients show discrepancies between measures. It also does not evaluate which measurement method is most clinically meaningful or predictive of outcomes, and its findings are limited to female patients, so generalizability to male patients remains unclear.
Why do individual patients show large discrepancies between measures, and what do these discrepancies reveal about disease heterogeneity or post-exertional malaise?
Do these measurement relationships and patterns differ in male ME/CFS patients, or in patients with different disease durations or severity levels?
Can these three measures help identify which patients are at higher risk for disease worsening or poor prognosis?