The aims were to determine during the popliteal angle (PA) tests whether particular knee muscles are activated and whether the position of pelvis affects the level of muscles activation. Twenty-two patients with cerebral palsy were recruited (age: 14±4.94 years). Knee muscle activities and range of motion were measured during PA. Knee flexors were active during tests, with fivefold increase of activation of ipsilateral hamstring. Higher and more frequent activation of muscles only in the contralateral limb was seen. Muscles activation should be considered as a confounding factor during tests. PA should not be relied upon as a major criterion for the treatment selection in cerebral palsy.