The present study aims to investigate the reproducibility of the following three isometric strength measurements in the upper extremity of children and adolescents with unilateral CP as well as in TDP: Hand Held Dynamometry (HHD), pinch and grip strength using the E-link system and functional strength. To study to which extent upper extremity strength, both in the affected side and the non-affected side, differs from the strength in the upper extremities of TDP, these measurements will also be performed by children without neurological problems.