Age-related longitudinal changes in metabolic energy expenditure during walking in boys with Duchenne muscular dystrophy.

Jiska C. E. Kempen,Erik H. Niks,Jaap Harlaar,Merel-Anne Brehm,Anneke J. van der Kooi,Janneke C. van den Bergen,Imelda J. M. de Groot,Jan J. G. M. Verschuuren

doi:10.1371/journal.pone.0115200

Abstract

ObjectiveThe 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.MethodsAt 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)).ResultsOver 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).ConclusionsThe 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.

Highlights

Duchenne muscular dystrophy (DMD) is the most common neuromuscular disease of childhood, affecting 1 in 5000 newborn boys [1]
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

Summary

Introduction

Duchenne muscular dystrophy (DMD) is the most common neuromuscular disease of childhood, affecting 1 in 5000 newborn boys [1]. Understanding the natural course of walking energy expenditure in DMD patients will assist in determining the need and timing of treatment interventions for boys whose walking energy expenditure is high. Such understanding is especially relevant, given that loss of ambulation in DMD occurs against a background of normal growth and maturation. [8, 9] Based on longitudinal data describing age-related declines in walking distance in boys with DMD [10,11,12,13,14], a progressive increase in walking energy expenditure is the expected natural course. Considering the age dependent biphasic pattern of evolution of walking performance reported in previous studies [13, 14], both the effects of time and age on walking energy expenditure were evaluated

Methods

Results

Conclusion