Minute-by-minute differences in co-activation during treadmill walking in cerebral palsy

The primary purpose of this study was to determine, in children and adolescents with mild spastic cerebra palsy (CP); 1) minute-by-minute differences in lower limb antagonist muscle co-activation and stride length (SL) during treadmill walking following 12-15 minutes of treadmill walking practice, and 2) if the minute-by-minute pattern of co-activation is affected by site (thigh or lower leg) and lower limb dominance. A secondary purpose was to determine if overall there is a difference in co-activation between the dominant and non-dominant lower limbs. Eight independently ambulatory children and adolescents with mild spastic CP (9.2-15.7 yr) participated in the study. Minute-by-minute lower limb antagonist muscle co-activation and SL were measured during a 3-minute treadmill walk at 90% of individually determined fastest treadmill walking speed. Non-dominant thigh (quadriceps, hamstring muscles) co-activation decreased between minute 1 and a) minute 2 (6%), b) minute 3 (7.2%). Co-activation for the dominant lower leg (tibialis anterior, triceps surae muscles) decreased between minute 1 and minute 3 (11.3%). Non-dominant thigh co-activation was on average 27.3% higher than for the dominant thigh. Thigh co-activation was on average 27.7% higher than for the lower leg, independent of dominance or time. SL increased between minute 1 and minute 3 by 2.1%. Twelve to 15 minutes of treadmill walking practice may be sufficient time to obtain stable co-activation and SL values by minute 2 of a fast treadmill walk. Dominance and site affect the magnitude of co-activation.