title: Decreased fractal correlation in diurnal physical activity in chronic fatigue syndrome.
abstract: OBJECTIVE
  Our objectives were to study the temporal correlation of physical activity time series in patients with chronic fatigue syndrome (CFS) during normal daily life and to examine if it could identify the altered physical activity in these patients.
  
  
  METHODS
  Fractal scaling exponents of diurnal and nocturnal physical activity time series in 10 CFS patients and 6 healthy control subjects (CON) were calculated by the detrended fluctuation analysis (DFA) and the wavelet transform modulus maxima (WTMM) method. We hypothesized that, due to their illness- and/or fatigue-induced resting episodes, altered physical activity patterns in CFS patients might be observed at the interruption of activity bursts. Thus, we further developed a new method, the wavelet transform negative modulus maxima (WTNMM) method, which could evaluate the temporal correlation at the interruption of activities. We compared the fractal scaling exponents for CFS and CON by each method.
  
  
  RESULTS
  Both for CFS and CON, we found the fractal time structures in their diurnal physical activity records for at least up to 35 minutes. No group difference was found in nocturnal activities. The WTNMM method revealed that, in diurnal activities, CFS patients had significantly (p < 0.01) smaller fractal scaling exponent (0.87 +/- 0.03) compared to controls (1.01 +/- 0.03). Such a difference was identified neither by the DFA nor WTMM method.
  
  
  CONCLUSIONS
  CFS patients had more abrupt interruptions of voluntary physical activity during diurnal periods in normal daily life, probed by the decreased correlation in the negative modulus maxima of the wavelet-transformed activity data, possibly due to their exaggerated fatigue.
authors.affiliation: Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. yamamoto@edcom.p.u-tokyo.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Ohashi
authors.forename: G
authors.initials: G
authors.lastname: Bleijenberg
authors.forename: S
authors.initials: S
authors.lastname: van der Werf
authors.forename: J
authors.initials: J
authors.lastname: Prins
authors.forename: L A N
authors.initials: LA
authors.lastname: Amaral
authors.forename: B H
authors.initials: BH
authors.lastname: Natelson
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
mesh_terms: D002908:Chronic Disease; D002940:Circadian Rhythm; D015673:Fatigue Syndrome, Chronic / Q000503:physiopathology*; D017709:Fractals; D006801:Humans; D008962:Models, Theoretical; D008991:Monitoring, Physiologic; D009043:Motor Activity / Q000502:physiology*; D012043:Regression, Psychology; D012815:Signal Processing, Computer-Assisted; D013223:Statistics as Topic; D013997:Time Factors