Assessment of neuromuscular response characteristics at the knee followinga functional perturbation

Previous research indicates that both the extent and timing of muscular act ivation at the knee can be influenced by muscle activity state, joint angle , weight-hearing status and trunk position. However, little research to dat e has evaluated protective neuromuscular response times and activation patt erns to an imposed perturbation with the knee joint in a functional, weight -bearing stance. Hence, we designed a lower extremity perturbation device t o produce a sudden, forward and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Surface elect romyography (EMG) recorded long latency reflex times of the medial and late ral quadriceps, hamstring and gastrocnemius muscles in 64 intercollegiate l acrosse and soccer players in response to both internal and external rotati on perturbation. We found the gastrocnemius fired significantly faster that the hamstring which in turn fired significantly faster than the quadriceps . There was also a significant difference in activation times of the medial and lateral hamstring not found for the quadriceps or gastrocnemius muscle s. Our findings confirmed that reactive neuromuscular responses following t his functional perturbation differ markedly from those previously reported using seated, partial weight-bearing and/or uni-planar models under relaxed conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.