Maintenance of elbow equilibrium through co-contraction

Experiments were conducted in which postures of the elbow and forearm were quasistatically maintained through deliberate cocontraction of the biceps and triceps, the principal flexor and extensor muscles acting about the elbow. The object of these experiments was to record the levels of muscular activation for the biceps and triceps as various postures of the elbow and forearm were maintained for a full range of cocontraction. Trials were conducted over a range of elbow angle from near fully flexed to near fully extended. Preliminary results from these experiments are presented. These show that for forearm postures away from the midrange of the elbow, cocontraction leads to antagonist muscle activation levels that, are significantly larger than the corresponding level of agonist activation i.e., the muscle supporting the limb against gravity is not working as hard as its antagonist counterpart. An explanation of these counterintuitive results is presented, based on assumed length-dependence of the muscle efficiency relating neural input to muscle force