Meeting Abstract
Sloths exhibit below branch walking whereby the limbs are required to support the entire body weight while in suspended posture. Suspensory habits therefore demand great strength and fatigue resistance of the limb flexors; however, the overall skeletal muscle mass of sloths is reduced. It is possible that sloths minimize active muscle recruitment and rely on tensile loading of muscle-tendon units to maintain suspension, thus reflecting a neuromuscular system tuned to conserve energy. Electromyography (EMG) activation was evaluated in a sample of N=6 three-toed sloths as an initial test of this hypothesis. EMG was recorded (via fire-wire electrodes) from eight forelimb muscles while sloths performed hanging, inverted walking, and vertical climbing. Our initial observations demonstrate that during hanging, all flexor/extensor muscles display minimal activity except for deltoideus (DELT) and extensor digitorum communis (EDC), which each show small bursts of activation. Most muscles are active during the contact phase of walking and have long bursts that typically occur after the footfall. Although active for a portion of limb contact, DELT, EDC, and triceps brachii have shorter bursts and also show activation during the swing phase. Compared with hanging and inverted walking, the majority of muscles show shorter and larger EMG bursts that may occur before or after each footfall during climbing. The exceptions to these activation patterns when sloths climb are that the biceps brachii and pectoralis superficialis exhibit sizable bursts with long burst durations. Additional evaluations will include quantification of EMG burst intensity and assessment of motor unit recruitment patterns using wavelet analysis techniques.
