| The purpose of this dissertation was to quantify joint rotational impedance (OO) through the calculation of muscle contributions to joint rotational impedance (MOO) both prior to (static), and following, the initiation of a mechanical perturbation (dynamic) about the knee and L4-L5 joints. Specifically, monitoring pre and post perturbation responses allowed for the evaluation of the neuromuscular reflex response contribution to MJRI, and ultimately quantify the magnitude of rotational impedance created by the involuntary component of the neuromuscular system.;Two additional studies investigated the individual muscle contributions to joint rotational impedance about the lumbar spine's L4-5 joint prior to, and following, sudden dynamic flexion and extension (Study 2) and right and left lateral bend (Study 3) perturbations to the trunk. Both studies showed that the response of the neuromuscular system, following forced trunk perturbations, was a significant contributor to MJRI.;It is concluded that the neuromuscular pre-voluntary response acts to initially stabilize the knee and L4-5 joints following sudden perturbations, albeit at lower joint rotational impedance magnitudes than found during the later voluntary, conscious response, in what is hypothesized to be an attempt to safely and quickly arrest motion of the perturbed segment. Also, when subjects were aware of perturbation timing, an anticipatory neuromuscular strategy was used, where subjects increasing their muscle forces just prior to the perturbation, thus enhancing joint rotational impedance before the disturbance.;Due to the complexity of the lumbar spine, it first seemed prudent to use a simpler joint system, i.e. the knee, to solidify methodological requirements for the quantification of dynamic MJRI. Study 1 was the first of three studies and was designed to investigate the neuromuscular response of a less complex system following a sudden perturbation. The results showed that the pre-voluntary responses of the leg muscles following the initial leg motion, responded through increased force production and, ultimately, enhanced total joint rotational impedance. |
