Abnormal Volitional Hip Torque Phasing and Hip

25 The purpose of this study was to quantify how volitional control of hip torque relates to 26 walking function post-stroke. Volitional phasing of hip flexion and extension torques was 27 assessed using a load-cell-instrumented servomotor drive system in 11 chronic stroke subjects 28 and 5 age-matched controls. Hips were oscillated from approximately 40 degrees of hip flexion 29 to 10 degrees of hip extension at a frequency of 0.50 Hz during three movement conditions (hips 30 inphase (IP), 180 degrees out of phase (OP), and unilateral hip movement (UN)) while the knees 31 and ankles were held stationary. The magnitude and phasing of hip, knee, and ankle torques were 32 measured during each movement condition. Surface electromyography was measured throughout 33 the legs. Over ground gait analysis was done for all stroke subjects. During robotic assisted 34 movement conditions, the paretic limb produced peak hip torques when agonist hip musculature 35 was stretched instead of midway through the movement as seen in the non-paretic and control 36 limbs (p < 0.012). However, mean torque magnitudes of the paretic and non-paretic limbs were 37 not significantly different. Abnormalities of paretic hip torque phasing were more pronounced 38 during bilateral movement conditions and were associated with quadriceps over-activity. The 39 magnitude of flexion torque produced during maximal hip extension was correlated with the 40 Fugl Meyer Score, self-selected walking speed, and maximal hip extension during over ground 41 walking. These results suggest that hyperexcitable stretch reflexes in the paretic limb impair 42 coordinated hip torque phasing and likely interfere with walking function post stroke. 43