Ahn A N, Konow N, Tijs C, Biewener A A
Concord Field Station, MCZ, Harvard University, 100 Old Causeway Road, Bedford, MA 01730, USA.
Department of Biology, Harvey Mudd College, 301 Platt Blvd, Claremont, CA 91711, USA.
Integr Comp Biol. 2018 Aug 1;58(2):219-231. doi: 10.1093/icb/icy040.
To relate in vivo behavior of fascicle segments within a muscle to their in vitro force-length relationships, we examined the strain behavior of paired segments within each of three vertebrate muscles. After determining in vivo muscle activity patterns and length changes of in-series segments within the semimembranosus muscle (SM) in the American Toad (Bufo americanus) during hopping and within the sternohyoid (SH) muscle in the rat (Rattus rattus) during swallowing, and of spatially separated fascicles within the medial gastrocnemius (MG) muscle in the rat during trotting, we measured their corresponding in vitro (toad) or in situ (rat) force-length relationships (FLRs). For all three muscles, in vivo strain heterogeneity lasted for about 36-57% of the behavior cycle, during which one segment or fascicle shortened while the other segment or fascicle simultaneously lengthened. In the toad SM, the proximal segment shortened from the descending limb across the plateau of its FLR from 1.12 to 0.91 of its optimal length (Lo), while the distal segment lengthened (by 0.04 ± 0.04 Lo) before shortening down the ascending limb from 0.94 to 0.83 Lo. In the rat SH muscle, the proximal segment tended to shorten on its ascending limb from 0.90 to 0.85 Lo while the distal segment tended to lengthen across Lo (0.96-1.12 Lo). In the rat MG muscle, in vivo strains of proximal fascicles ranged from 0.72 to 1.02 Lo, while the distal fascicles ranged from 0.88 to 1.11 Lo. Even though the timing of muscle activation patterns were similar between segments, the heterogeneous strain patterns of fascicle segments measured in vivo coincided with different operating ranges across their FLRs simultaneously, implying differences in force-velocity behavior as well. The three vertebrate skeletal muscles represent a diversity of fiber architectures and functions and suggest that patterns of in vivo contractile strain and the operating range over the FLR in one muscle region does not necessarily represent other regions within the same muscle.
为了将肌肉内肌束节段的体内行为与其体外力-长度关系联系起来，我们研究了三种脊椎动物肌肉中每块肌肉内成对节段的应变行为。在确定美洲蟾蜍（Bufo americanus）跳跃过程中半膜肌（SM）内串联节段以及大鼠（Rattus rattus）吞咽过程中胸骨舌骨肌（SH）内串联节段的体内肌肉活动模式和长度变化，以及大鼠小跑过程中腓肠肌内侧头（MG）肌肉内空间分离的肌束的体内肌肉活动模式和长度变化之后，我们测量了它们相应的体外（蟾蜍）或原位（大鼠）力-长度关系（FLR）。对于所有三块肌肉，体内应变异质性持续约行为周期的36 - 57%，在此期间一个节段或肌束缩短，而另一个节段或肌束同时延长。在蟾蜍的半膜肌中，近端节段从其FLR的下降支越过平台缩短，从其最佳长度（Lo）的1.12缩短至0.91，而远端节段在从0.94缩短至0.83 Lo的上升支之前先延长（0.04±0.04 Lo）。在大鼠的胸骨舌骨肌中，近端节段在其从0.90至0.85 Lo的上升支上倾向于缩短，而远端节段倾向于在Lo（0.96 - 1.12 Lo）范围内延长。在大鼠的腓肠肌内侧头肌中，近端肌束的体内应变范围为0.72至1.02 Lo，而远端肌束的体内应变范围为0.88至1.11 Lo。尽管节段之间肌肉激活模式的时间相似，但体内测量的肌束节段的异质应变模式与它们FLR上不同的工作范围同时吻合，这也意味着力-速度行为存在差异。这三块脊椎动物骨骼肌代表了多种纤维结构和功能，并表明一块肌肉中一个区域的体内收缩应变模式和FLR上的工作范围不一定代表同一肌肉内的其他区域。
