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Children with developmental coordination disorder have less variable motor unit firing rate characteristics across
Maaike Esselaar1,2, Johnny V V Parr1,2, Greg Wood1,2
1Department of Sport and Exercise Sciences, Manchester Metropolitan University, Manchester, United Kingdom.
Insights
Children with developmental coordination disorder (DCD) showed similar average motor unit characteristics but less variability in firing compared to typically developing peers. This suggests a more rigid force control strategy in DCD.
Area of Science:
- Neuroscience
- Developmental Pediatrics
- Motor Control
Background:
- Developmental Coordination Disorder (DCD) is linked to altered skeletal muscle activity, indicating unique motor control strategies in affected children.
- Understanding motor unit recruitment and firing rates is key to elucidating DCD's neuromuscular control nuances.
- Previous research has not deeply explored fine motor unit function details in children with DCD.
Purpose of the Study:
- To compare motor unit characteristics during low-level handgrip contractions in typically developing (TD) children and children with DCD.
- To investigate differences in motor unit firing rates and control strategies between these groups.
Main Methods:
- Eighteen children (9 TD, 9 DCD) performed handgrip contractions at 10% of maximum voluntary contraction.
- High-density surface electromyography recorded muscle activity in the first dorsal interosseous muscle.
- Motor unit action potential trains were decomposed to analyze characteristics like firing rate and inter-pulse interval, controlling for force steadiness (coefficient of variation <10%).
Main Results:
- No significant differences were found in average motor unit number, firing rate, or inter-pulse interval between TD and DCD groups, despite age differences.
- Children with DCD exhibited significantly less variability in motor unit firing statistics (inter-pulse interval coefficient of variation) compared to TD children.
- The DCD group displayed a more consistent, less variable motor unit firing pattern across contractions.
Conclusions:
- Despite similar average motor unit function, children with DCD may employ a more fixed or rigid strategy to stabilize force.
- Reduced variability in motor unit firing in DCD warrants further investigation into its role in motor control and grasping tasks.
- Future research should explore the implications of motor unit firing variability in DCD and typically developing children.
Introduction:
Understanding the nuances of neuromuscular control is crucial in unravelling the complexities of developmental coordination disorder (DCD), which has been associated with differences in skeletal muscle activity, implying that children with DCD employ distinct strategies for muscle control. However, force generation and control are dependent on both recruitment of motor units and their firing rates and these fine details of motor function have yet to be studied in DCD. The purpose of this study was therefore to compare motor unit characteristics in a small muscle of the hand during low level, handgrip contractions in typically developing (TD) children and children with DCD.
Methods:
Eighteen children (9 TD vs. 9 DCD) completed a series of manual handgrip contractions at 10 ± 5% of their maximum voluntary contraction. High density surface electromyography was used to record excitation of the first dorsal interosseus muscle. Recorded signals were subsequently decomposed into individual motor unit action potential trains. Motor unit characteristics (firing rate, inter-pulse interval, and action potential amplitude) were analysed for contractions that had a coefficient variation of <10%.
Results And Discussion:
This study found few differences in average motor unit characteristics (number of motor units: TD 20.24 ± 9.73, DCD 27.32 ± 14.00; firing rate: TD 7.74 ± 2.16 p.p.s., DCD 7.86 ± 2.39 p.p.s.; inter-pulse interval: TD 199.72 ± 84.24 ms, DCD 207.12 ± 103 ms) when force steadiness was controlled for, despite the DCD group being significantly older (10.89 ± 0.78 years) than the TD group (9.44 ± 1.67 years). However, differences were found in the variability of motor unit firing statistics, with the children with DCD surprisingly showing less variability across contractions (standard deviation of coefficient of variation of inter-pulse interval: TD 0.38 ± 0.12, DCD 0.28 ± 0.11). This may suggest a more fixed strategy to stabilise force between contractions used by children with DCD. However, as variability of motor unit firing has not been considered in previous studies of children further work is required to better understand the role of variability in motor unit firing during manual grasping tasks, in all children.
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