Barclay C J
Department of Physiology, Monash University, Clayton, Victoria, Australia.
J Exp Biol. 1994 Aug;193:65-78. doi: 10.1242/jeb.193.1.65.
The mechanical efficiency of mouse fast- and slow-twitch muscle was determined during contractions involving sinusoidal length changes. Measurements were made of muscle length, force production and initial heat output from bundles of muscle fibres in vitro at 31 degrees C. Power output was calculated as the product of the net work output per sinusoidal length cycle and the cycle frequency. The initial mechanical efficiency was defined as power output/(rate of initial heat production+power output). Both power output and rate of initial heat production were averaged over a full cycle of length change. The amplitude of length changes was +/- 5% of muscle length. Stimulus phase and duration were adjusted to maximise net work output at each cycle frequency used. The maximum initial mechanical efficiency of slow-twitch soleus muscle was 0.52 +/- 0.01 (mean +/- 1 S.E.M. N = 4) and occurred at a cycle frequency of 3 Hz. Efficiency was not significantly different from this at cycle frequencies of 1.5-4 Hz, but was significantly lower at cycle frequencies of 0.5 and 1 Hz. The maximum efficiency of fast-twitch extensor digitorum longus muscle was 0.34 +/- 0.03 (N = 4) and was relatively constant (0.32-0.34) over a broad range of frequencies (4-12 Hz). A comparison of these results with those from previous studies of the mechanical efficiency of mammalian muscles indicates that efficiency depends markedly on contraction protocol.
在涉及正弦长度变化的收缩过程中，测定了小鼠快肌和慢肌的机械效率。在31摄氏度下，对体外肌肉纤维束的肌肉长度、力量产生和初始热量输出进行了测量。功率输出通过每个正弦长度周期的净功输出与周期频率的乘积来计算。初始机械效率定义为功率输出/（初始产热速率+功率输出）。功率输出和初始产热速率在一个完整的长度变化周期内进行平均。长度变化的幅度为肌肉长度的±5%。调整刺激相位和持续时间，以在每个使用的周期频率下使净功输出最大化。慢肌比目鱼肌的最大初始机械效率为0.52±0.01（平均值±1标准误，N = 4），出现在3 Hz的周期频率下。在1.5 - 4 Hz的周期频率下，效率与该值无显著差异，但在0.5和1 Hz的周期频率下显著降低。快肌趾长伸肌的最大效率为0.34±0.03（N = 4），在较宽的频率范围（4 - 12 Hz）内相对恒定（0.32 - 0.34）。将这些结果与先前关于哺乳动物肌肉机械效率的研究结果进行比较表明，效率明显取决于收缩方案。
