Article

PURPOSE: To investigate the muscle size-strength relationship of the knee flexors
and extensors in children with spastic cerebral palsy (CP) in relation to
typically developing children (TD). METHODS: Eighteen children with spastic
Diplegia, Gross Motor Function Classification System I-III (mean 7 y 5 mo SD 1 y
7 mo) and 19 TD children (mean 7 y 6 mo SD 1 y 9 mo) participated. Muscle volume
(MV) and anatomical cross-sectional area (aCSA) were assessed using MRI. Measures
of peak torque (PT) and work of the knee flexors and extensors were assessed
isometrically and isokinetically using a Biodex dynamometer, and normalised to
bodymass (Bm). RESULTS: Children with CP were weaker than their TD peers across
all torque variables (p < 0.05). MV and aCSA of the knee flexors (MV: p = 0.002;
aCSA: p = 0.000) and extensors (MV: p = 0.003; aCSA: p < 0.0001) were smaller in
children with CP. The relationship between muscle size and strength in children
with CP was weaker than the TD children. The strongest relationship was between
MV and isometric PT/Bm for TD children (r = 0.77-0.84), and between MV and
isokinetic work (r = 0.70-0.72) for children with CP. CONCLUSIONS: Children with
CP have smaller, weaker muscles than their TD peers. However, muscle size may
only partially explain their decreased torque capacity. MV appears to be a better
predictor of muscle work in children with CP than aCSA. This is an important area
of research particularly in regard to treatment(s) that target muscle and
strength in children with CP. Implications for Rehabilitation This research adds
to the evidence that children with CP have smaller, weaker knee flexor and
extensor muscles than their TD peers. However, unlike their TD peers, muscle size
does not necessarily relate to muscle strength. The weak correlation between
MRI-derived muscle volume and isometric peak torque suggests children with CP are
underpowered relative to their muscle size. For children with CP, muscle volume
appears to be the best predictor of isokinetic muscle torque output. Therefore,
when assessing the capacity of a muscle, it appears preferable to measure total
muscle volume and torque development through a range of motion (isokinetic
strength).

Langue : ANGLAIS