Nguyen Anh D, Gray Aubrey, Sawicki Gregory, Franz Jason R
Lampe Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, Chapel Hill, NC, United States.
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States.
PeerJ. 2025 Aug 21;13:e19842. doi: 10.7717/peerj.19842. eCollection 2025.
Age-related deficits in Achilles tendon stiffness have been linked to shorter calf muscle operating lengths. These shorter lengths have the potential to precipitate higher requisite excitations and thereby an earlier onset of local fatigability in older adults. However, the connection between calf muscle operating lengths and muscle fatigability has yet to be systematically explored, even in healthy younger adults. Thus, the goal of this study was to establish a mechanistic pathway between soleus fascicle length, prescribed herein using changes in ankle joint angle, and muscle fatigue in a cohort of younger adults.
Participants performed repeated fixed-end calf muscle contractions to task failure in a computerized robotic dynamometer at two ankle joint angles to prescribe relatively shorter (., 15° plantarflexion (PF15)) and longer (., 15° dorsiflexion (DF15)) soleus fascicle lengths.
On average, moving from DF15 to PF15 elicited 14% shorter muscle fascicle lengths, a roughly two-fold higher EMG rms amplitude, significant but modest reductions in EMG median frequency, and a 60% reduction in time to task failure (-values < 0.05). These findings may have clinical relevance for mechanisms associated with higher metabolic costs and increased fatigability among older adults, who often operate their calf muscles at shorter fascicle lengths due to lesser Achilles tendon stiffness. As a roadmap for comparison and hypothesis generation, this study sets the stage for future work in older adults.
跟腱僵硬度与年龄相关的下降与小腿肌肉较短的工作长度有关。这些较短的长度有可能促使更高的必要兴奋度，从而使老年人更早出现局部疲劳。然而，即使在健康的年轻人中，小腿肌肉工作长度与肌肉疲劳之间的联系尚未得到系统研究。因此，本研究的目的是在一组年轻人中建立比目鱼肌束长度（此处用踝关节角度变化来规定）与肌肉疲劳之间的机制途径。
参与者在计算机控制的机器人测力计上，在两个踝关节角度下进行重复的固定末端小腿肌肉收缩，直至任务失败，以规定相对较短（如，15°跖屈（PF15））和较长（如，15°背屈（DF15））的比目鱼肌束长度。
平均而言，从DF15到PF15，肌肉束长度缩短14%，肌电图均方根振幅大约高出两倍，肌电图中位频率有显著但适度的降低，任务失败时间减少60%（P值<0.05）。这些发现可能与老年人中较高代谢成本和疲劳增加相关的机制具有临床相关性，老年人由于跟腱僵硬度较低，其小腿肌肉常以较短的肌束长度工作。作为比较和假设生成的路线图，本研究为未来在老年人中的研究奠定了基础。
