Marsh R L, Olson J M
Department of Biology, Northeastern University, Boston, MA 02115.
J Exp Biol. 1994 Aug;193:139-56. doi: 10.1242/jeb.193.1.139.
Because measurements on isolated skeletal muscles are often made with limited knowledge of in vivo kinematics, predictions of mechanical performance during natural movements are subject to considerable uncertainties. We used information on the in vivo length cycle and phase of activation of the scallop adductor during swimming at 10 degrees C to design an in vitro contractile regime that replicated the natural cycle. Replicating the in vivo length cycle and stimulation regime resulted in power output during cyclic contractions that matched in vivo performance both qualitatively and quantitatively. When sinusoidal length changes were used instead of the natural length trajectory, the adductor muscle produced a similar average power output (approximately 30 W kg-1 at 1.9 Hz), but the distribution of power throughout the cycles was quite different. We examined the instantaneous force-velocity properties during cyclic contractions and found that the muscle operated on or near its isotonic force-velocity curve for only 30-40% of the time required for shortening. During sinusoidal length cycles, the force-velocity trajectory was quite different. We conclude that during cyclic contractions the isotonic force-velocity curve of skeletal muscle sets an approximate boundary to the force-velocity trajectory, but the shape of this trajectory, and thus the distribution of power output, depends on the pattern of length change.
由于在对分离的骨骼肌进行测量时，往往对体内运动学了解有限，因此对自然运动过程中机械性能的预测存在相当大的不确定性。我们利用在10摄氏度游泳时扇贝内收肌的体内长度周期和激活阶段的信息，设计了一种体外收缩模式，该模式复制了自然周期。复制体内长度周期和刺激模式导致周期性收缩期间的功率输出在定性和定量上都与体内性能相匹配。当使用正弦长度变化而非自然长度轨迹时，内收肌产生了相似的平均功率输出（在1.9赫兹时约为30瓦/千克），但整个周期内的功率分布却大不相同。我们研究了周期性收缩期间的瞬时力-速度特性，发现肌肉在缩短所需时间的30%-40%内仅在其等张力力-速度曲线上或附近运行。在正弦长度周期期间，力-速度轨迹则大不相同。我们得出结论，在周期性收缩期间，骨骼肌的等张力力-速度曲线为力-速度轨迹设定了一个近似边界，但该轨迹的形状以及因此功率输出的分布取决于长度变化模式。
