title: Estimation of muscle strength from actigraph data in Duchenne muscular dystrophy.
abstract: BACKGROUND
  The purpose of this study was to evaluate the utility of a wrist actigraph for estimating muscle strength in Duchenne muscular dystrophy patients.
  
  
  METHODS
  Twenty-two patients aged 4-19 years wore a wrist actigraph to monitor activities of daily living, and underwent a test of knee extension strength and the 6 min walk test. These measures were made at baseline and at 1 year later. The actigraph data were quantified using the zero crossing mode (ZCM), which indicates the frequency of movement, and the proportional integration mode (PIM), which indicates activity level or vigor of motion.
  
  
  RESULTS
  The ZCM and PIM scores of ambulatory patients were higher than those of non-ambulatory patients (P < 0.001). The correlation coefficient between ZCM score and 6 min walk distance, ZCM score and knee extension strength, PIM score and 6 minute walk distance, and PIM score and knee extension strength was -0.44, 0.25, 0.58, and 0.63, respectively. This indicates that the PIM score had a moderate-good association with 6 min walk distance and knee extension strength.
  
  
  CONCLUSIONS
  Muscle strength can be estimated using the PIM score calculated from actigraph data. The PIM score is a good tool for the estimation of muscle strength.
authors.affiliation: Department of Child Development, Kumamoto University Graduate School, Kumamoto, Japan.
authors.forename: Shigemi
authors.initials: S
authors.lastname: Kimura
authors.forename: Shiro
authors.initials: S
authors.lastname: Ozasa
authors.forename: Keiko
authors.initials: K
authors.lastname: Nomura
authors.forename: Kowashi
authors.initials: K
authors.lastname: Yoshioka
authors.forename: Fumio
authors.initials: F
authors.lastname: Endo
mesh_terms: D056044:Actigraphy; D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D006801:Humans; D053580:Muscle Strength; D020388:Muscular Dystrophy, Duchenne / Q000503:physiopathology*; D055815:Young Adult
keywords: Duchenne muscular dystrophy; actigraph; muscle strength; proportional integration mode; six minute walk test