“The problem with running”—Comparing the propulsion strategy of children with Developmental Coordination Disorder and typically developing children
Introduction
Developmental Coordination Disorder (DCD) is a neurodevelopmental disorder associated with impaired motor co-ordination in the absence of other diagnoses [1], [2]. The motor impairments create difficulties with functional tasks such as gait and activities of daily living [3], [4].
The generation of muscle power and recycling of energy during adult gait has been a recent topic of research. The ankle plantarflexors typically dominate joint power generation at the end of stance to propel the center of mass forwards in push-off [5]. The hip joint also contributes power for propulsion taking advantage of the inertia of the pelvis to pull the thigh forwards on the pelvis (“pull-off”). Peak hip power generation at “pull-off” is typically about one third of ankle power generated at push-off [6], [7]. When gait velocity increases, increased power for propulsion is met by the generation of greater plantarflexor and hip flexor power, with the increased plantarflexor power beginning earlier in the gait cycle [8].
The plantarflexor muscles recycle mechanical energy through storage and release of energy in the Achilles tendon during the stance phase of gait [7]. If plantarflexor power generation at push-off is impaired, a compensatory strategy such as hip flexor work during pre-swing is required for forward propulsion, although the gait pattern is less efficient due to the relatively higher metabolic cost of pulling the lower limb forwards compared with using the elasticity of plantarflexor musculotendinous unit [7]. Compensatory use of hip flexor power in generating propulsion during gait has been observed in the elderly, attributed to the loss of elasticity of the Achilles tendon[9], and in children with Down syndrome, attributed to muscle hypotonia [10].
Children with DCD have been observed to walk more slowly with a shorter step length compared to typically developing (TD) children [4] and with less active ankle range of movement [3], [4]. Boys with DCD have shown deficits of power generation at the ankle during push off during slow running [11]. Poor ankle power and compensatory hip flexor power at push off in gait could explain the propensity for lower levels of physical activity in children with DCD [12]. The aim of this study was to investigate strategies of power generation during usual and fast speeds of walking and running in children with DCD and who are TD.
Section snippets
Methods
Eleven children (6 male) with DCD and 11 TD age- and gender-matched children between 9 and 13 years old were recruited. All children had no diagnosed neurological, musculoskeletal or cognitive disorder affecting their gait, and had a body mass index (BMI) between the 5th–85th percentile for their age-gender group representing “healthy weight” [13]. Children with DCD were recruited from two ongoing studies being conducted at Curtin University, and from physiotherapists and occupational
Results
The groups (DCD and TD) were similar in age (p = 0.770), height (p = 0.201) and weight (p = 0.414). The NDI score of the TD group was on average 44 points higher than those in the DCD group (p < 0.001) (Table 1). As expected, gait speed increased when the children moved from normal walking to fast walking and from jogging and to sprinting for both groups of children (Table 2). Both groups walked at similar speeds however in general children who were TD used a greater range of running speeds compared
Discussion
We found that the children with DCD used a different propulsion strategy compared with children who were TD. This was characterized by poor use of ankle plantarflexor and compensatory hip flexor power at push off, particularly evident during jogging and running. We calculated a derived variable for propulsion strategy which may prove a useful tool for evaluating the effect of interventions on gait.
The difference in propulsion strategy between children with DCD and TD children was particularly
Sources of support
None.
Acknowledgements
We would like to thank the children together with their families and caregivers who participated in the study. We also acknowledge staff from Curtin University and the therapists who assisted with recruiting.
Conflict of interest statement
There are no conflicts of interest.
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