Difference in bilateral upper limb muscle activation during the assisting hand assessement in children affected by unilateral cerebral palsy
INTRODUCTION Cerebral palsy (CP) refers to a group of childhood-onset disorders that affect an individual’s ability to move and maintain posture due to a brain lesion occurring during in utero development. When the lesion affects motor areas on one side of the brain, an impairment of movement and posture will be manifested on the contralateral side. The most common CP condition is called unilateral cerebral palsy (UCP), leading to challenges with daily activities due to decreased function  and use of their affected upper limb. The purpose of this study was to evaluate side-to-side muscle activation differences during the Assisting Hand Assessment (AHA), a performance based assessment that measures how children with upper limb impairments use their involved limb as an assisting hand during bimanual activities .
CLINICAL SIGNIFICANCE As a visual tool, the AHA provides qualitative information regarding the upper extremity functionality of a child with UCP. Discrepancies in side-to-side muscle activation provides a way to quantify the AHA tasks that is unattainable with visual analysis alone.
METHODS Thirteen patients diagnosed with UCP were tested. Muscle activation was measured via electromyography (EMG) sensors (Delsys Trigno Wireless, Boston, MA, USA) placed bilaterally on the biceps (BIC), triceps (TRI), wrist extensors (EXT), and wrist flexor (FLE) muscles. Tasks of the AHA were assessed individually as shown in Table 1. The EMG sensors measured the electrical activity of each muscle in micro-volts (µV) at 3,000 Hz. EMG signals were rectified and filtered to compute a linear envelope, and mean and maximum values were computed for both limbs using a representative trial per task. To determine side-to-side differences, a symmetry ratio (affected vs. unaffected) was computed and Wilcoxon signed-ranked tests were performed to identify significant differences using an α level of 0.05.
RESULTS Side-to-side differences in muscle activation were observed across tasks, primarily for the biceps, wrist extensor, and wrist flexor muscle groups. Specifically, differences in biceps and wrist flexor muscle activation were observed in 50% and 42% of tasks, respectively, while wrist extensor muscle activation significantly differed between sides across all tasks. Notably, only three tasks resulted in sideto-side differences solely in the wrist extensor muscle group, including the Car (p = 0.001), Cymbals (p = 0.016), and String Toy (p = 0.004) tasks. Alternatively, triceps differences were not significant with the exception of the Rip Paper task (p = 0.019). Symmetry ratios for the triceps also indicated increased activation on the affected side for 9 of the 12 tasks, while the affected side exhibited decreased activation compared to the unaffected side for the majority of tasks in the remaining muscle groups.
DISCUSSION These results indicate that side-to-side differences in muscle activation are more exaggerated in specific tasks of the AHA, especially in the Rip Paper task that involves both limbs to move similarly in opposite directions. Therefore, certain tasks may provide more information to guide rehabilitation that focuses on muscle recruitment and strength. Additionally, while wrist extensor muscle activation differed bilaterally across all tasks, sideto-side differences in the remaining muscle groups varied across tasks, indicating the importance of evaluating the full AHA rather than focusing on one or two components of the assessment. It is also important to note that differences in triceps muscle activation could have been limited due to a lack of AHA tasks requiring substantial elbow extension and thus, deep triceps muscle contraction. Future work will explore the use of motion capture to quantify additional compensatory mechanisms such as trunk displacement.