Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, St. Lucia, QLD 4072, Brisbane, Australia;
Human Movement Science, Faculty of Sport Science, Ruhr-University Bochum, 44801 Bochum, Nordrhein-Westfalen, Germany.
Proc Natl Acad Sci U S A. 2018 Apr 3;115(14):E3097-E3105. doi: 10.1073/pnas.1712697115. Epub 2018 Mar 19.
The factors that drive variable aponeurosis behaviors in active versus passive muscle may alter the longitudinal stiffness of the aponeurosis during contraction, which may change the fascicle strains for a given muscle force. However, it remains unknown whether these factors can drive variable aponeurosis behaviors across different muscle-tendon unit (MTU) lengths and influence the subsequent fascicle strains during contraction. Here, we used ultrasound and elastography techniques to examine in vivo muscle fascicle behavior and central aponeurosis deformations of human tibialis anterior (TA) during force-matched voluntary isometric dorsiflexion contractions at three MTU lengths. We found that increases in TA MTU length increased both the length and apparent longitudinal stiffness of the central aponeurosis at low and moderate muscle forces ( < 0.01). We also found that increased aponeurosis stiffness was directly related to reduced magnitudes of TA muscle fascicle shortening for the same change in force ( < 0.01). The increase in slope and shift to longer overall lengths of the active aponeurosis force-length relationship as MTU length increased was likely due to a combination of parallel lengthening of aponeurosis and greater transverse aponeurosis strains. This study provides in vivo evidence that human aponeurosis stiffness is increased from low to moderate forces and that the fascicle strains for a given muscle force are MTU length dependent. Further testing is warranted to determine whether MTU length-dependent stiffness is a fundamental property of the aponeurosis in pennate muscles and evaluate whether this property can enhance muscle performance.
在主动和被动肌肉中驱动可变肌腱行为的因素可能会改变收缩过程中肌腱的纵向刚度，从而改变给定肌肉力下的肌束应变。然而，目前尚不清楚这些因素是否可以在不同的肌腱-肌腹单元（MTU）长度下驱动可变肌腱行为，并影响收缩过程中的后续肌束应变。在这里，我们使用超声和弹性成像技术来检查三种 MTU 长度下，力匹配的自愿等长背屈收缩过程中，人体胫骨前肌（TA）的肌束行为和中央肌腱的变形。我们发现，随着 TA MTU 长度的增加，在低中和中等肌肉力量（<0.01）下，中央肌腱的长度和表观纵向刚度都增加了。我们还发现，随着肌腱刚度的增加，相同力的变化下，TA 肌束缩短的幅度减小（<0.01）。随着 MTU 长度的增加，主动肌腱力-长度关系的斜率增加和整体长度向更长的方向移动，这可能是由于肌腱的平行延长和更大的横向肌腱应变的共同作用。本研究提供了人体肌腱刚度从低到中等力量增加的体内证据，并且给定肌肉力的肌束应变与 MTU 长度有关。需要进一步的测试来确定 MTU 长度依赖性的刚度是否是羽状肌肌腱的基本特性，并评估该特性是否可以增强肌肉性能。
