Experimental design

In all individuals, paired 120-s EMG recordings from the investigated upper limb were obtained during attempted rest in three different positions; a maximally flexed position of the elbow, a 90-degree joint angle and a maximally extended position. The experimenter fixated the arm in the positions by supporting the subject’s arm. In the flexed and extended positions, the experimenters made sure that the position did not cause any discomfort to the individual due to contractures and physical constraints of joint position. Between each resting recording the arm was held in a maximally flexed position for a minimum of 20 s before being placed in a new position. EMG recordings were started as soon as the individual’s arm was placed in a new position. Furthermore, all control individuals were asked to perform 120 s of low-force static contractions against resistance from the experimenter corresponding to approximately 10% of maximum voluntary contraction in each position at the end of the experiment. These recordings were performed to obtain a measure of the EMG–EMG coherence from an isometric voluntary contraction of the biceps muscle that was comparable with the EMG–EMG coherence measures obtained from individuals with CP or stroke exhibiting sustained muscle activity during rest.