Background and rationale 

The two most common congenital childhood neurodevelopmental motor disorders are developmental coordination disorder (DCD) and cerebral palsy (CP). In both pathologies, the children experience gait abnormalities. In children with CP these gait abnormalities are visually obvious, while for children with DCD problems with automatization of gait become more apparent when performing a dual task. In typically developing children (TDC), automatization of gait by the central nervous system is linked to muscle synergies: groups of muscles that are activated together to perform a rhythmic motor task. This ability to selectively and timely activate the required muscles for a task is coined selective motor control (SMC). SMC during gait (SMCg) increases with gait maturation in TDC, but not always in CP. Overall, children with CP have impaired SMCg compared to TDC. Though not yet investigated in children with DCD, lack of SMCg could underlie the difficulties these children have with dual tasking.

Research questions 

1) What are the effects of double tasking on gait automatization in TDC, CP, and DCD children? 

How do 2) TDC as well as 3) DCD and CP children walk and perform a concurrent task?  

4) To what extent is SMCg related to this dual task performance? 

Method 

To assess the current state of the art on the topic, a systematic review will be performed on the first research question. Following, for a cross-sectional study, 63 children (21 TDC, 21 DCD, 21 CP; effect size=1.04, power=0.95, α=0.05), aged 7-18 will be recruited. Children with DCD (M-ABC-2 ≤ 5th percentile) and children with hemiplegic CP Gross Motor Functional Classification Scale Level I-II will be included. Measurements will take place at the UZ Gent’s SmartSpace while walking on an instrumented split-belt treadmill (GRAIL, Motek). The embedded force plates, a 10-camera VICON-system, 32 surface EMG (sEMG) electrodes will collect the kinetics, kinematics, and muscle activation respectively. The sEMG data will be collected from 16 muscles bilaterally of the trunk, upper, and lower limbs and will provide the input for quantifying SMCg. During a single session on the GRAIL the children will 1) perform a single task (walking) as well as 2) a cognitive dual task, like the STROOP test, and 3) a motor dual task requiring the use of the upper limbs while walking in a virtual environment projected onto the large semi-cylindrical screen of the GRAIL. Gait deviation scores will be determined based on kinetics and kinematics. SMCg will be assessed by extracting muscle synergies from sEMG data with (weighted) non-negative matrix factorization ((W)NMF). Gait deviations, dual task performance, and SMCg will be compared between groups using independent group statistics as well as explored per group for the effect of age using correlation analysis.