Interrelationships among thigh muscle co-contraction, quadriceps muscle strength and the aerobic demand of walking in children with cerebral palsy.

The purpose of this study was to quantify interrelationships among thigh muscle co-contraction, quadriceps muscle strength, and the aerobic demand of walking in 13 children with spastic hemiplegic cerebral palsy (CP). During Session 1, subjects were familiarized with testing procedures, given five minutes of treadmill walking practice, and completed quadriceps muscle strength testing. In Session 2, subjects performed three 5-min walking bouts on the treadmill at 0.67 m x s(-1) to further accommodate to treadmill ambulation. During Session 3, resting VO2 was measured and subjects walked at 0.67, 0.89, and 1.12 m x s(-1) for five minutes while oxygen uptake (VO2) and thigh muscle co-contraction data were collected. Results demonstrated that no significant relationship existed between net VO2 and measures of thigh muscle co-contraction or quadriceps muscle strength. In addition, thigh muscle co-contraction was not shown to be associated with quadriceps muscle strength. Collectively, thigh muscle co-contraction and quadriceps muscle strength explained 13. 5%, 6.2%, and 2.2% of the variance in VO2 at 0.67, 0.89, and 1.12 m x s(-1), respectively. Viewed in concert, these results suggest that the walking energy expenditure of children with spastic hemiplegic CP is not influenced by the level of thigh muscle co-contraction or quadriceps muscle strength.