School of Kinesiology, University of Michigan, Ann Arbor, MI, USA.
Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
J Anat. 2021 Aug;239(2):479-488. doi: 10.1111/joa.13455. Epub 2021 May 19.
The pectoralis major fiber regions contribute uniquely to the mobility and the stability of the shoulder complex. It is unknown how age and sex influence the stiffness of these regions during volitional contractions, but this knowledge is critical to inform clinical interventions targeting the pectoralis major. The aim of the present study was to determine if the activation-dependent stiffness of the pectoralis major fiber regions differs between the sexes and if it is altered with age. Ultrasound shear wave elastography was used to acquire shear wave velocity from the clavicular and the sternocostal fiber regions of 48 healthy participants, including 24 younger (12 males, 12 females, mean ± SD age 25 ± 4.1 years) and 24 older adults (12 males, 12 females, 55 ± 3.6 years). Participants performed vertical adduction and horizontal flexion torques in neutral and 90° externally rotated shoulder positions, and one of the two shoulder abduction positions (60° and 90°) at varying torque magnitudes (passive, 15% and 30% of maximal voluntary contraction). Separate linear mixed-effects models were run for each fiber region and shoulder position to determine if the activation-dependent stiffness differed between the sexes and was altered in older adults. Age-related alterations in stiffness during volitional contractions were observed in both fiber regions and were dependent on the task. Alterations in activation-dependent stiffness due to age were more pronounced in females than males. Additionally, females had greater stiffness than males during volitional contractions in both fiber regions. The present findings provide the first line of evidence that the activation-dependent stiffness of the pectoralis major fiber regions is influenced by sex and changes with age.
胸大肌纤维区域对肩部复合体的活动性和稳定性有独特的贡献。目前尚不清楚年龄和性别如何影响这些区域在自主收缩过程中的刚度，但这一知识对于针对胸大肌的临床干预措施至关重要。本研究的目的是确定胸大肌纤维区域的激活依赖性刚度是否存在性别差异，以及其是否随年龄而改变。超声剪切波弹性成像用于从锁骨和胸骨肋纤维区域获取 48 名健康参与者的剪切波速度，包括 24 名年轻参与者（12 名男性，12 名女性，平均年龄 25 ± 4.1 岁）和 24 名老年参与者（12 名男性，12 名女性，55 ± 3.6 岁）。参与者在中立位和 90°外旋位进行垂直内收和水平前屈扭矩，以及两种肩外展位之一（60°和 90°），施加不同的扭矩大小（被动，15%和 30%最大自主收缩）。针对每个纤维区域和肩部位置分别运行线性混合效应模型，以确定激活依赖性刚度是否存在性别差异，以及在老年参与者中是否发生改变。在两种纤维区域和依赖于任务的情况下，都观察到了自主收缩过程中与年龄相关的刚度改变。由于年龄引起的激活依赖性刚度改变在女性中比男性更为明显。此外，在两种纤维区域中，女性在自主收缩过程中的刚度都大于男性。本研究结果首次提供了证据，表明胸大肌纤维区域的激活依赖性刚度受到性别和年龄变化的影响。
