Key result
During elbow flexion in goats, the lateral head stretched (5 +/- 2%) to absorb work, while the long head shortened (-7 +/- 1%) to produce work, demonstrating functional diversification.
Functional diversification can arise between mono- and biarticular muscle agonists operating at the same joint, with the long head producing power and the lateral head resisting flexion and absorbing work.
Goat muscle diversification findings remain preclinical; leaves open translation to human biomechanics or clinical practice.
We investigate how the biarticular long head and monoarticular lateral head of the triceps brachii function in goats (Capra hircus) during jumping and landing. Elbow moment and work were measured from high-speed video and ground reaction force (GRF) recordings. Muscle activation and strain were measured via electromyography and sonomicrometry, and muscle stress was estimated from elbow moment and by partitioning stress based on its relative strain rate. Elbow joint and muscle function were compared among three types of limb usage: jump take-off (lead limb), the step prior to jump take-off (lag limb), and landing. We predicted that the strain and work patterns in the monoarticular lateral head would follow the kinematics and work of the elbow more closely than would those of the biarticular long head. In general this prediction was supported. For instance, the lateral head stretched (5 +/- 2%; mean +/- SE) in the lead and lag limbs to absorb work during elbow flexion and joint work absorption, while the long head shortened (-7 +/- 1%) to produce work. During elbow extension, both muscles shortened by similar amounts (-10 +/- 2% long; -13 +/- 4% lateral) in the lead limb to produce work. Both triceps heads functioned similarly in landing, stretching (13 +/- 3% in the long head and 19 +/- 5% in the lateral) to absorb energy. In general, the long head functioned to produce power at the shoulder and elbow, while the lateral head functioned to resist elbow flexion and absorb work, demonstrating that functional diversification can arise between mono- and biarticular muscle agonists operating at the same joint.
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Carroll et al. (2008) studied this question. Limb usage (jump take-off, step prior to take-off, landing) vs. Comparison between monoarticular lateral head and biarticular long head was evaluated on Muscle strain and work patterns. During elbow flexion in goats, the lateral head stretched (5 +/- 2%) to absorb work, while the long head shortened (-7 +/- 1%) to produce work, demonstrating functional diversification.
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