This investigation developed a measure of motor control for the knee extensors in adults with cerebral palsy (CP). Four adults with CP and 4 able-bodied (AB) adults participated. A KinCom dynamometer rotated the knee from approximately 90º of knee flexion to 10º/s less than the participant’s maximum knee extension at a speed of 10º/s, while the participant attempted to match a 44.5-N “target” force. The average, standard deviation, and median frequency of the force-time data were used to describe the test results. The individual force values for the AB group were near the target force and clustered together. The values for the CP group were also near the target force, but displayed greater variation. The average standard deviation for the CP group was more than three times larger than that of the AB group. The average median frequency for the CP group was less than that of the AB group. Results pointed to differing strategies for each group as they attempted to match the target force. The AB group attempted to match the target force with frequent small-magnitude force changes, while the CP group attempted to match the target force with fewer oscillations of greater magnitude. The methods employed in the present investigation are initial attempts to quantify one aspect of motor control, a visually guided tracking task.
The authors are with Barnes-Jewish Hospital in St. Louis. Jack R. Engsberg is Director of the Human Performance Laboratory, Barnes-Jewish Hospital, 4555 Forest Park Parkway, St. Louis, MO 63108.