title: Ambulatory monitoring of physical activity and symptoms in fibromyalgia and chronic fatigue syndrome.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Medical and Clinical Psychology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA. wjkop@usuhs.mil
authors.forename: Willem J
authors.initials: WJ
authors.lastname: Kop
authors.forename: Angela
authors.initials: A
authors.lastname: Lyden
authors.forename: Ali A
authors.initials: AA
authors.lastname: Berlin
authors.forename: Kirsten
authors.initials: K
authors.lastname: Ambrose
authors.forename: Cara
authors.initials: C
authors.lastname: Olsen
authors.forename: Richard H
authors.initials: RH
authors.lastname: Gracely
authors.forename: David A
authors.initials: DA
authors.lastname: Williams
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Clauw
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D005221:Fatigue; D015673:Fatigue Syndrome, Chronic / Q000503:physiopathology*; D005260:Female; D005356:Fibromyalgia / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory; D009043:Motor Activity; D010146:Pain / Q000503:physiopathology; D012720:Severity of Illness Index; D012890:Sleep; D011795:Surveys and Questionnaires