Muscle fatigue during repetitive voluntary contractions: a comparison between children with cerebral palsy, typically developing children and young healthy adults.

Aim: To combine peak torque and EMG analyses to investigate the hypothesis that 1) children with cerebral palsy (CP) have lower muscle fatigability than typically developing children (TD) and whether 2) muscle fatigue correlates with muscle strength. Methods: Seven CP children, eight TD children and ten young healthy adults (YHA) performed an all-out fatigue test of 35 maximal concentric knee extension and flexion contractions on an isokinetic dynamometer. Angular velocity was set at 60°/s. Peak torque (PT) was determined per repetition and either normalized to bodyweight or maximum voluntary torque. Surface-EMG of quadriceps and hamstring muscles was measured to obtain changes in median frequency (EMG- mf) and smooth rectified EMG amplitude per contraction. Results: Decline in PT differed between all groups for extensors and flexors, where YHA showed the largest decline and CP children the smallest decline over the course of the test. YHA showed a larger decline in EMG- mf of all quadriceps and hamstrings than TD and CP children, while TD children showed a larger decline in EMG- mf of m.rectus femoris and m.vastus lateralis than CP children. Interpretation: Results confirm that children with CP show lower fatigability than TD children and that the lower fatigability coincides with lower maximal muscle strength. © 2013 Elsevier B.V.