Sport and Exercise Science Research Centre, School of Applied Sciences, London South Bank University, London, UK.
Department of Training and Movement Sciences, Humboldt-Universität zu Berlin, Berlin, Germany.
Scand J Med Sci Sports. 2024 May;34(5):e14638. doi: 10.1111/sms.14638.
This study aimed to examine the temporal dynamics of muscle-tendon adaptation and whether differences between their sensitivity to mechano-metabolic stimuli would lead to non-uniform changes within the triceps surae (TS) muscle-tendon unit (MTU). Twelve young adults completed a 12-week training intervention of unilateral isometric cyclic plantarflexion contractions at 80% of maximal voluntary contraction until failure to induce a high TS activity and hence metabolic stress. Each participant trained one limb at a short (plantarflexed position, 115°: PF) and the other at a long (dorsiflexed position, 85°: DF) MTU length to vary the mechanical load. MTU mechanical, morphological, and material properties were assessed biweekly via simultaneous ultrasonography-dynamometry and magnetic resonance imaging. Our hypothesis that tendon would be more sensitive to the operating magnitude of tendon strain but less to metabolic stress exercise was confirmed as tendon stiffness, Young's modulus, and tendon size were only increased in the DF condition following the intervention. The PF leg demonstrated a continuous increment in maximal AT strain (i.e., higher mechanical demand) over time along with lack of adaptation in its biomechanical properties. The premise that skeletal muscle adapts at a higher rate than tendon and does not require high mechanical load to hypertrophy or increase its force potential during exercise was verified as the adaptive changes in morphological and mechanical properties of the muscle did not differ between DF and PF. Such differences in muscle-tendon sensitivity to mechano-metabolic stimuli may temporarily increase MTU imbalances that could have implications for the risk of tendon overuse injury.
本研究旨在探讨肌肉-肌腱适应的时间动态变化，以及它们对机械代谢刺激的敏感性差异是否会导致三腿头肌-肌腱单位（MTU）内的非均匀变化。12 名年轻人完成了一项为期 12 周的单侧等长循环跖屈收缩训练干预，收缩强度为最大自主收缩的 80%，直至疲劳，以诱导三腿头肌高度活跃和代谢应激。每位参与者用一条腿进行短（跖屈位置，115°：PF），另一条腿进行长（背屈位置，85°：DF）MTU 长度的训练，以改变机械负荷。每周通过超声-动力测量和磁共振成像同步评估 MTU 的机械、形态和材料特性。我们的假设是，肌腱对肌腱应变的作用幅度更敏感，但对代谢应激运动的敏感性较低，这一假设得到了证实，因为只有在干预后 DF 条件下，肌腱硬度、杨氏模量和肌腱大小才会增加。PF 腿的最大 AT 应变（即更高的机械需求）随着时间的推移持续增加，同时其生物力学特性没有适应。骨骼肌的适应速度高于肌腱，并且在运动中不需要高机械负荷来肥大或增加其力潜能的前提得到了验证，因为 DF 和 PF 之间肌肉形态和机械特性的适应性变化没有差异。肌肉-肌腱对机械代谢刺激的敏感性差异可能会暂时增加 MTU 的不平衡，这可能会增加肌腱过度使用损伤的风险。
