Konow Nicolai, Collias Alexandra, Biewener Andrew A
Department of Biological Sciences, University of Massachusetts Lowell, Lowell, MA, United States.
Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Bedford, MA, United States.
Front Physiol. 2020 Mar 20;11:143. doi: 10.3389/fphys.2020.00143. eCollection 2020.
Contractions of skeletal muscles to generate movement involve dynamic changes in contractile and elastic tissue strains that likely interact to influence the force and work of a muscle. However, studies of the dynamics of skeletal muscle and tendon strains remain largely limited to bipedal animals, and rarely cover the broad spectra of movement requirements met by muscles that operate as motors, struts, or brakes across the various gaits that animals commonly use and conditions they encounter. Using high-speed bi-planar fluoromicrometry, we analyze strains within the rat medial gastrocnemius (MG) across a range of gait and slope conditions. These conditions require changes in muscle force ranging from decline walk (low) to incline gallop (high). Measurements are made from implanted (0.5-0.8 mm) tantalum spheres marking MG mid-belly width, mid-belly thickness, as well as strains of distal fascicles, the muscle belly, and the Achilles tendon. During stance, as the muscle contracts, muscle force increases linearly with respect to gait-slope combinations, and both shortening and lengthening fiber strains increase from approximately 5 to 15% resting length. Contractile change in muscle thickness (thickness strain) decreases ( = 0.86; = 0.001); whereas, the change in muscle width (width strain) increases ( = 0.88; = 0.001) and tendon strain increases ( = 0.77; = 0.015). Our results demonstrate force-dependency of contractile and tendinous tissue strains with compensatory changes in shape for a key locomotor muscle in the hind limb of a small quadruped. These dynamic changes are linked to the ability of a muscle to tune its force and work output as requirements change with locomotor speed and environmental conditions.
骨骼肌收缩以产生运动涉及收缩组织和弹性组织应变的动态变化，这些变化可能相互作用以影响肌肉的力量和功。然而，对骨骼肌和肌腱应变动态的研究在很大程度上仍局限于双足动物，很少涵盖作为发动机、支柱或制动器的肌肉在动物常用的各种步态和所遇到的条件下满足的广泛运动需求范围。我们使用高速双平面荧光显微镜，分析了大鼠内侧腓肠肌（MG）在一系列步态和坡度条件下的应变。这些条件要求肌肉力量从下坡行走（低）到上坡飞奔（高）发生变化。测量是通过植入的（0.5 - 0.8毫米）钽球进行的，这些钽球标记了MG肌腹宽度、肌腹厚度以及远端肌束、肌腹和跟腱的应变。在站立阶段，随着肌肉收缩，肌肉力量相对于步态 - 坡度组合呈线性增加，并且缩短和伸长的纤维应变均从大约5%静息长度增加到15%静息长度。肌肉厚度的收缩变化（厚度应变）减小（ = 0.86； = 0.001）；而肌肉宽度的变化（宽度应变）增加（ = 0.88； = 0.001），肌腱应变增加（ = 0.77； = 0.015）。我们的结果表明，对于小型四足动物后肢的关键运动肌肉，收缩组织和肌腱组织应变存在力依赖性，且形状有补偿性变化。这些动态变化与肌肉根据运动速度和环境条件变化调整其力量和功输出的能力相关。
