Department of Medical and Clinical Psychology, Uniformed Services University
of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA.
wjkop@usuhs.mil
Abstract
OBJECTIVE: Fibromyalgia (FM) and chronic fatigue syndrome (CFS) are
associated with substantial physical disability. Determinants of
self-reported physical disability are poorly understood. This investigation
uses objective ambulatory activity monitoring to compare patients with FM
and/or CFS with controls, and examines associations of ambulatory activity
levels with both physical function and symptoms during activities of daily
life.
METHODS: Patients with FM and/or CFS (n = 38, mean +/- SD age 41.5 +/- 8.2
years, 74% women) completed a 5-day program of ambulatory monitoring of
physical activity and symptoms (pain, fatigue, and distress) and results
were compared with those in age-matched controls (n = 27, mean +/- SD age
38.0 +/- 8.6 years, 44% women). Activity levels were assessed continuously,
ambulatory symptoms were determined using electronically time-stamped
recordings at 5 time points during each day, and physical function was
measured with the 36-item Short Form health survey at the end of the 5-day
monitoring period.
RESULTS: Patients had significantly lower peak activity levels than controls
(mean +/- SEM 8,654 +/- 527 versus 12,913 +/- 1,462 units; P = 0.003) and
spent less time in high-level activities when compared with controls (P =
0.001). In contrast, patients had similar average activity levels as those
of controls (mean +/- SEM 1,525 +/- 63 versus 1,602 +/- 89; P = 0.47). Among
patients, low activity levels were associated with worse self-reported
physical function over the preceding month. Activity levels were inversely
related to concurrent ambulatory pain (P = 0.031) and fatigue (P < 0.001).
Pain and fatigue were associated with reduced subsequent ambulatory activity
levels, whereas activity levels were not predictive of subsequent symptoms.
CONCLUSION: Patients with FM and/or CFS engaged in less high-intensity
physical activities than that recorded for sedentary control subjects. This
reduced peak activity was correlated with measures of poor physical
function. The observed associations may be relevant to the design of
behavioral activation programs, because activity levels appear to be
contingent on, rather than predictive of, symptoms.
