title: Age-related longitudinal changes in metabolic energy expenditure during walking in boys with Duchenne muscular dystrophy.
abstract: OBJECTIVE
  The aim of this study was to evaluate age-related changes in metabolic walking energy expenditure in ambulant boys affected by Duchenne muscular dystrophy over a follow-up period of 12 months.
  
  
  METHODS
  At baseline (T1) and 12 months later (T2), metabolic walking energy expenditure was assessed during a 6-minute walk test at comfortable speed in 14 ambulant boys with Duchenne (age range: 6.0-12.5 years, mean 8.2). Outcome measures derived from the assessment included the 6-minute comfortable walking distance (m) and net-nondimensional energy cost relative to speed-matched control cost (SMC-EC, %). Statistical comparisons were made using a two-way repeated measures ANOVA (factors: time (T1 versus T2) and age (<8 years of age (yoa) versus ≥8 yoa)).
  
  
  RESULTS
  Over the course of the study, a significant decrease of -28m (-8.2%, p = 0.043) was noted in the walked distance at comfortable speed. Besides, SMC-EC increased with 4.4%, although this change was not significant (p = 0.452). Regarding age groups, boys below 8 yoa showed a smaller annual decrease in the walked distance (-15 m) compared to boys above 8 yoa (-37 m). SMC-EC increased with 10% in the older boys, while in the younger boys it decreased (-2.1%). The main effect of age group on walking distance and SMC-EC however was not significant (p>0.158), and also there were no interaction effects (p>0.248).
  
  
  CONCLUSIONS
  The results of our small study suggest that the natural course of walking performance in ambulant boys with Duchenne is characterized by a decrease in comfortable walking distance and an increase in walking energy cost. The rate of energy cost seems to increase with age, while walking distance decreases, which is opposite from the trend in typically developing children.
authors.affiliation: Department of Rehabilitation Medicine and MOVE Research Institute, VU University Medical Center, Amsterdam, The Netherlands; Department of Rehabilitation, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Merel-Anne
authors.initials: MA
authors.lastname: Brehm
authors.affiliation: Department of Rehabilitation Medicine and MOVE Research Institute, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Jiska C E
authors.initials: JC
authors.lastname: Kempen
authors.affiliation: Department of Neurology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Anneke J
authors.initials: AJ
authors.lastname: van der Kooi
authors.affiliation: Department of Rehabilitation, Radboud University Medical Center Nijmegen, The Netherlands.
authors.forename: Imelda J M
authors.initials: IJ
authors.lastname: de Groot
authors.affiliation: Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Janneke C
authors.initials: JC
authors.lastname: van den Bergen
authors.affiliation: Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Jan J G M
authors.initials: JJ
authors.lastname: Verschuuren
authors.affiliation: Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Erik H
authors.initials: EH
authors.lastname: Niks
authors.affiliation: Department of Rehabilitation Medicine and MOVE Research Institute, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Jaap
authors.initials: J
authors.lastname: Harlaar
mesh_terms: D000367:Age Factors; D002648:Child; D004734:Energy Metabolism / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D020388:Muscular Dystrophy, Duchenne / Q000503:physiopathology*; D016138:Walking / Q000502:physiology*