Meeting Abstract
Sloths exhibit below branch locomotion and postures whereby fore- and hindlimb pairs equally support their body weight. Suspensory habits require both strength and fatigue resistance of the limb flexors, yet muscle mass is reduced in sloths. It is then possible that sloths minimize muscle activation during tensile loading of muscle-tendon units to maintain support, thus indicating potential neuromuscular specializations for conserving energy. Electromyography (EMG) was evaluated in three-toed sloths (Bradypus variegatus: N=6) to test this hypothesis. EMG was recorded (2000Hz) via fire-wire electrodes implanted into 8 forelimb muscles while sloths performed suspensory hanging and walking, and vertical climbing. Video recordings (100Hz) were synchronized with EMG to mark footfalls for a total of 227 strides analyzed. EMG activation for each muscle was normalized to peak activation recorded across behaviors. B. variegatus demonstrates that flexor/extensor muscles are minimally activated during hanging. Compared to hanging, EMG activation in the forelimb flexors doubles during suspensory walking and increases by a factor of 1.3 during vertical climbing. Overall, the elbow flexors mm. biceps brachii and brachioradialis show the greatest EMG activation, and these large bursts occurred during suspensory walking, while burst intensity was more similar (within 5–15%) between walking and climbing for the m. pectoralis superficialis, biarticular m. triceps brachii long head, and the digital extensors. Activation of the elbow flexors, in particular, may be critical for stabilizing forces acting on the forelimbs during suspension. Further evaluations will include assessment of recruitment frequencies of slow and fast motor units using wavelet analysis.
