Children with Cerebral Palsy (CP) experience limitations in motor activities and participation in the community, predominantly caused by impairments in muscle function. Aside from abnormal posturing due to spasticity, muscle weakness can significantly contribute to impaired muscle function and there is increasing evidence that muscle weakness significantly impairs upper limb motor function and ability to perform manual tasks in children with CP. Studies in the last decade have shown that muscle weakness, not spasticity, is the greatest limiting factor of motor function in children with CP. Furthermore, there is increasing evidence that the strength in the upper extremities of children with CP is less compared to their typically developing peers (TDP). A systematic review focused on the psychometric properties of strength measurement instruments has shown that the number of studies investigating psychometric properties of strength measurement instruments is limited and that the methodological quality of these studies is low.