Ashley-Ross M A, Barker J U
Department of Biology, Box 7325, Wake Forest University, Winston-Salem, NC 27109, USA.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2002 Sep;188(8):611-20. doi: 10.1007/s00359-002-0336-4. Epub 2002 Aug 24.
Most vertebrate muscles are composed of a mixture of fiber types. However, studies of muscle mechanics have concentrated on homogeneous bundles of fibers. Hindlimb muscles of the tiger salamander, Ambystoma tigrinum, present an excellent system to explore the consequences of fiber heterogeneity. Isometric twitches and work loops were obtained in vitro from two muscles, the m. iliotibialis pars posterior (heterogeneous, containing types I, IIa and IIb fibers) and the m. iliofibularis (nearly homogeneous for type IIa fibers). Maximal isometric twitch and tetanic stresses in m. iliotibialis posterior were significantly greater than in iliofibularis. Work loops were obtained over a range of frequencies (0.5-3.0 Hz) and strains (2-6% muscle length) that encompassed the observed ranges in vivo. Work per cycle from the homogeneous iliofibularis declined from 1.5-3.0 Hz, while that from the heterogeneous m. iliotibialis posterior increased from 0.5 Hz to 2.5 Hz and declined at 3.0 Hz. Power output from the iliofibularis rose with frequency to at least 3 Hz; power from the iliotibialis posterior rose with frequency to 2.5 Hz and declined thereafter. Mass-specific work per cycle and power output were higher in iliofibularis than iliotibialis posterior over most frequencies and strains tested.
大多数脊椎动物的肌肉是由多种纤维类型混合而成的。然而，肌肉力学的研究主要集中在纤维的同质束上。虎螈（Ambystoma tigrinum）的后肢肌肉为探索纤维异质性的影响提供了一个绝佳的系统。在体外从两块肌肉中获取了等长收缩和功环数据，这两块肌肉分别是胫髂肌后段（异质的，包含I型、IIa型和IIb型纤维）和髂腓肌（几乎同质的IIa型纤维）。胫髂肌后段的最大等长收缩和强直应力显著大于髂腓肌。在一系列频率（0.5 - 3.0 Hz）和应变（肌肉长度的2 - 6%）范围内获取了功环数据，这些范围涵盖了在体内观察到的范围。同质的髂腓肌每周期的功在1.5 - 3.0 Hz范围内下降，而异质的胫髂肌后段每周期的功从0.5 Hz增加到2.5 Hz，并在3.0 Hz时下降。髂腓肌的功率输出随频率增加至少到3 Hz；胫髂肌后段的功率随频率增加到2.5 Hz，此后下降。在测试的大多数频率和应变下，髂腓肌每周期的质量比功和功率输出高于胫髂肌后段。
