Motor control of the lower extremity musculature in children with cerebral palsy.
Kids with CP show messy ankle torque and muscle firing, so check steadiness before you add balance or gait loads.
01Research in Context
What this study did
Researchers asked kids with cerebral palsy to push their foot against a fixed pedal. They measured how steady the push was and recorded muscle firing with surface EMG.
The same test was given to typically developing kids for comparison. The goal was to see if ankle control looks different in CP.
What they found
Kids with CP could not hold a steady push. Their ankle torque wobbled far more than that of peers.
The EMG signal also showed a different rhythm. The muscles fired in a less organized pattern, hinting at weak motor planning.
How this fits with other research
Van de Winckel et al. (2013) used fMRI on kids with unilateral CP and found the brain lights up on both sides during simple moves. Tassé et al. (2013) now show the ankle itself is shaky, so the extra brain work seen by Ann may be a compensation for poor peripheral control.
Granieri et al. (2020) saw similar force wobble in the hands of children with ASD. The pattern repeats: when the brain gives noisy commands, every limb can wobble, whether it is the ankle in CP or the fingers in ASD.
Hong et al. (2011) found the same variability in speech muscles. From ankle to jaw, CP adds noise to the motor signal.
Why it matters
If the ankle is unsteady, balance and gait drills may fail until the child can first hold a steady push. Start with short isometric holds against your hand or a pedal and give real-time visual bars so the client can see the wobble and correct it.
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02At a glance
03Original abstract
The aim of this investigation was to quantify the differences in torque steadiness and variability of the muscular control in children with cerebral palsy (CP) and typically developing (TD) children. Fifteen children with CP (age=14.2±0.7 years) that had a Gross Motor Function Classification System (GMFCS) score of I-III and 15 age and gender matched TD children (age=14.1±0.7 years) participated in this investigation. The participants performed submaximal steady-state isometric contractions with the ankle, knee, and hip while surface electromyography (sEMG) was recorded. An isokinetic dynamometer was used to measure the steady-state isometric torques while the participants matched a target torque of 20% of the subject's maximum voluntary torque value. The coefficient of variation was used to assess the amount of variability in the steady-state torque, while approximate entropy was used to assess the regularity of the steady-state torque over time. Lastly, the distribution of the power spectrum of the respective sEMG was evaluated. The results of this investigation were: 1) children with CP had a greater amount of variability in their torque steadiness at the ankle than TD children, 2) children with CP had a greater amount of variability at the ankle joint than at the knee and hip joint, 3) the children with CP had a more regular steady-state torque pattern than TD children for all the joints, 4) the ankle sEMG of children with CP was composed of higher harmonics than that of the TD children.
Research in developmental disabilities, 2013 · doi:10.1016/j.ridd.2012.12.014