Society for Experimental Biology Annual Main Meeting 28th June — 1st July 2009, Glasgow, UK A7 — INTEGRATION OF ACTIVE AND PASSIVE CONTROL MECHANISMS IN LOCOMOTION

By virtue of the hierarchical design of the motor system, the control of coordination is distributed to the brain, spinal cord and the architectural features of the musculoskeletal system. Force feedback forms one such coordinating network in the spinal cord. Positive force feedback is mainly autogenic and increases muscular and limb stiffness and promote propulsion during locomotion. In contrast, intermuscular, inhibitory force feedback in principle increases limb compliance and promotes interjoint coordination. Experiments in cats suggest that during walking uphill, positive force feedback is more broadly distributed than in level walking. During walking downhill, where muscles serve a braking function and the interaction with the ground can be destabilizing, inhibitory force feedback predominates and controls the interaction between the body and the ground. Therefore, force feedback is subject to neural modulation according to the context of motor control. Deep fascia provides an architectural mechanism to promote coordination. Fascia distributes muscular forces outside of tendons and aponeuroses and provides an additional route for mechanical feedback. Force transmission through fascia depends on the state of activation of the muscles to which it is attached. Acute disruption of the crural fascia in the stepping premammillary cat results in a loss of stability, particularly in the mediolateral direction. The affected limb tends to wander more widely during treadmill stepping. Given the problem of controlling endpoint forces with muscles that cross different axes of rotation and joints, fascia appears to constrain these degrees of freedom and therefore simplifies motor coordination. Email Address for correspondence: [email protected]