Mechanical and neural factors underlying muscle performance during submaximal voluntary shortening contractions

次最大自愿缩短收缩期间肌肉表现的机械和神经因素

• 批准号: 447345165
• 负责人: Dr. Brent James Raiteri, Ph.D.
• 金额: --
• 依托单位: Lehr- und Forschungsbereich Bewegungslehre und Biomechanik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/447345165?language=en
• 关键词: Mechanical; neural; factors; underlying; muscle

Many everyday movements require that muscles change length while producing force to accelerate or decelerate the body, yet our ability to predict in vivo muscle force under these conditions is poor. This might be because the conventional muscle models used to predict muscle force typically neglect the muscle’s history of length change, which affects the muscle’s force-producing capacity and its underlying neural control. Specifically, following active muscle shortening, force output is depressed compared with what is expected based on generally-accepted theories of muscle contraction. This phenomenon is termed residual force depression (rFD) and our current understanding of how rFD affects neuromuscular performance is incomplete. This is because we typically assess a muscle’s maximum force-producing capacity under constant muscle-tendon unit (MTU) length conditions and we neglect that MTU compliance permits muscle shortening under these conditions, which induces rFD. Consequently, we underestimate the true in vivo isometric force capacity of human locomotor muscles and we fail to account for the changes in neuromuscular function that might occur due to rFD. This current lack of understanding contributes to inaccurate muscle force predictions during everyday movements, which severely limits our ability to effectively restore, improve and supplement human movement across the lifespan. This project therefore aims to uncover how rFD interacts with (I) the muscle’s force-producing capacity, (II) the upstream excitability of the motor cortex and spinal cord, and (III) the muscle’s underlying neural drive. These aims will be addressed across four studies that will systematically manipulate human tibialis anterior (a major dorsiflexor muscle important for walking and postural control) in vivo muscle lengths, length changes and muscle activity levels while the excitability of the corticospinal system and the muscle’s motor unit behaviour are probed with a unique combination of cutting-edge experimental techniques from biomechanics and neurophysiology (e.g. ultrasound imaging, non-invasive brain and spinal cord stimulation, high-density surface electromyography). Preliminary results indicate that muscle shortening during submaximal voluntary fixed-end contractions induces rFD due to MTU compliance, which might subsequently increase corticospinal excitability and change motor unit behaviour compared with constant muscle length contraction conditions. This effect of rFD on neuromuscular function has previously been neglected and is useful information for developing more effective strategies to enhance muscle performance, reduce injury risk or prevent age-and-disability-related functional decline. This research is also important for advancing current neuromusculoskeletal models, which are used to interpret muscle function during everyday movements and assess the consequences of clinical conditions, as well as inform surgical planning and mechatronic design.

许多日常运动需要肌肉改变长度，同时产生力量来加速或减速身体，但我们预测在这些条件下体内肌肉力量的能力很差。这可能是因为用于预测肌肉力量的传统肌肉模型通常忽略了肌肉长度变化的历史，这会影响肌肉的力量产生能力及其潜在的神经控制。具体而言，在主动肌肉缩短之后，与基于普遍接受的肌肉收缩理论的预期相比，力输出被抑制。这种现象被称为残余力抑制（rFD），我们目前的理解是如何影响rFD神经肌肉性能是不完整的。这是因为我们通常在恒定的肌肉-肌腱单位（MTU）长度条件下评估肌肉的最大产力能力，而我们忽略了MTU顺应性允许肌肉在这些条件下缩短，这会诱导rFD。因此，我们低估了真正的人体运动肌肉在体内的等长力量的能力，我们不能解释的神经肌肉功能的变化，可能会发生由于rFD。目前缺乏了解导致日常运动中的肌肉力量预测不准确，这严重限制了我们在整个生命周期中有效恢复，改善和补充人类运动的能力。因此，该项目旨在揭示rFD如何与（I）肌肉的产力能力、（II）运动皮质和脊髓的上游兴奋性以及（III）肌肉的潜在神经驱动相互作用。这些目标将通过四项研究来解决，这些研究将系统地操纵人类胫骨前肌（对于行走和姿势控制重要的主要背屈肌）体内肌肉长度，长度的变化和肌肉活动水平，而皮质脊髓系统的兴奋性和肌肉的运动单位的行为是从生物力学和神经生理学的尖端实验技术的独特组合探讨（例如超声成像、非侵入性脑和脊髓刺激、高密度表面肌电图）。初步结果表明，肌肉缩短在次最大自愿固定端收缩诱导rFD由于MTU的顺应性，这可能随后增加皮质脊髓兴奋性和改变运动单位的行为相比，恒定的肌肉长度收缩条件。rFD对神经肌肉功能的这种影响以前被忽视，这对于开发更有效的策略以增强肌肉性能、降低损伤风险或预防与年龄和残疾相关的功能下降是有用的信息。这项研究对于推进当前的神经肌肉骨骼模型也很重要，这些模型用于解释日常运动中的肌肉功能，评估临床状况的后果，以及为手术规划和机电设计提供信息。