Assessment of passive hip flexion. Manually-applied force (top) and hip flexion range of motion (ROM) (bottom) traces of the involved and uninvolved side of a femoroacetabular impingement patient. The horizontal dotted lines indicate the target force (mean of the two warm-up trials). ROM was calculated as the mean angle during the 1-s interval between "a" and "b", where "b" is the greatest ROM. Note that ROM is greater for the uninvolved than for the involved side.