Mechanical and electrical studies on the horse : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University

Abstract

Muscle forces may have profound influences on stress and strain within the muscle - skeletal system of an animal. These forces have previously been measured by indirect methods often with severe restrictions on the type of movement (if any) that the skeleton was allowed to undergo. A direct method of muscle force (or tendon tension) measurement in the conscious animal was sought which did not necessitate restriction of skeletal movement. This project reports the manufacture and successful in vivo functioning of a tendon tension 'buckle' transducer. The use of the device was demonstrated by correlating tension in the common digital extensor tendon with strain on the lateral and medial aspects of the bone of the walking horse. Strain was monitored by bonding foil electrical resistance strain gauges to the bone surface using a contact cement. The swing and support phases of the forelegs were monitored by switches attached to each forefoot and occasionally monitored by cinematography. Thus it was possible to make a detailed analysis of the lateral bone strain recording in terms of body weight bearing and of muscle action via the monitored tendon. Also considered were the influences of tension in other tendons of the limb and the action of the head and neck during walking. A further application of the tendon tension transducer was its use in monitoring tendon tension during recordings of the electrical activity generated by the corresponding muscle. This activity, which was recorded from intramuscular wire electrodes, was later rectified, integrated and compared with the directly measured force. Experience in electromyography was gained through extensive studies of the equine larynx during which the instrumentation was improved. The early attempts at bonding strain gauges and flanges to living equine bone failed because the epoxy resin flanges which held the lead wires became detached from the bone. The epoxy resin mouldings were consequently screwed in place but this caused slight lameness immediately following surgery. Experiments with a tendon tension transducer proved fruitless until the 'buckle' configuration was adopted. This device, when suitably constructed, did not significantly affect the gait of the animal.