Human Movement Science, Faculty of Sport Science, Ruhr-Universität Bochum, Bochum, Nordrhein-Westfalen, Germany.
School of Human Movement and Nutrition Sciences, University of Queensland, Brisbane, Queensland, Australia.
PeerJ. 2023 Jul 13;11:e15693. doi: 10.7717/peerj.15693. eCollection 2023.
Knowledge of the muscle's lengths at which maximum active isometric force is attained is important for predicting forces during movement. However, there is limited information about the force-length properties of a human muscle that plays crucial roles during locomotion; the tibialis anterior (TA). We therefore aimed to estimate TA's force-length relation from dorsiflexor torque-angle curves constructed from eight women and eight men.
Participants performed maximal voluntary fixed-end contractions with their right ankle dorsiflexors from 0° to 30° plantar flexion. Muscle fascicle lengths were estimated from B-mode ultrasound images, and net ankle joint torques were measured using dynamometry. Fascicle forces were estimated by dividing maximal active torques by literature-derived, angle-specific tendon moment arm lengths while assuming a fixed 50% force contribution of TA to the total dorsiflexor force and accounting for fascicle angles.
Maximal active torques were higher at 15° than 20° and 30° plantar flexion (2.4-6.4 Nm, ≤ 0.012), whereas maximal active TA fascicle forces were higher at 15° than 0°, 20° and 30° plantar flexion (25-61 N, ≤ 0.042), but not different between 15° and 10° plantar flexion (15 N, = 0.277). TA fascicle shortening magnitudes during fixed-end contractions were larger at 15° than 30° plantar flexion (3.9 mm, = 0.012), but less at 15° than 0° plantar flexion (-2.4 mm, = 0.001), with no significant differences (≤0.7 mm, = 0.871) between TA's superficial and deep muscle compartments. Series elastic element stiffness was lowest and highest at lengths 5% shorter and 5% longer than optimum fascicle length, respectively (-30 and 15 N/mm, ≤ 0.003).
TA produced its maximum active force at 10-15° plantar flexion, and its normalized force-length relation had ascending and descending limbs that agreed with a simple scaled sarcomere model when active fascicle lengths from within TA's superficial or deep muscle compartment were considered. These findings can be used to inform the properties of the contractile and series elastic elements of Hill-type muscle models.
了解肌肉在达到最大主动等长力时的长度对于预测运动中的力很重要。然而，对于在运动中起关键作用的人体肌肉的力-长度特性，人们知之甚少；胫骨前肌（TA）就是其中之一。因此，我们旨在从 8 名女性和 8 名男性的背屈扭矩-角度曲线中估算 TA 的力-长度关系。
参与者从 0°到 30°跖屈以最大自主固定端收缩他们的右脚踝背屈肌。肌肉肌束长度从 B 型超声图像估计，踝关节净转矩使用测力法测量。肌束力通过将最大主动转矩除以文献中特定角度的肌腱矩臂长度来估计，同时假设 TA 对总背屈力的贡献固定为 50%，并考虑肌束角度。
20°和 30°跖屈时的最大主动转矩（2.4-6.4 Nm，≤0.012）低于 15°，而 15°跖屈时的最大主动 TA 肌束力（25-61 N，≤0.042）高于 0°、20°和 30°，但 15°和 10°跖屈时没有差异（15 N，=0.277）。固定端收缩时 TA 肌束的缩短幅度在 15°时大于 30°跖屈（3.9 mm，=0.012），但在 15°时小于 0°跖屈（-2.4 mm，=0.001），但在浅层和深层肌肉之间没有显著差异（≤0.7 mm，=0.871）。串联弹性元件的刚度在比最佳肌束长度短 5%和长 5%时最低和最高（-30 和 15 N/mm，≤0.003）。
TA 在 10-15°跖屈时产生最大主动力，当考虑 TA 浅层或深层肌肉内的主动肌束长度时，其归一化力-长度关系具有上升和下降支，与简单的比例化肌节模型一致。这些发现可用于为 Hill 型肌肉模型的收缩和串联弹性元件的特性提供信息。
