Carroll Andrew M, Biewener Andrew A
Department of Biology, University of Evansville, 1800 Lincoln Avenue, Evansville, IN 47722, USA.
J Exp Biol. 2009 Oct;212(Pt 20):3349-60. doi: 10.1242/jeb.033639.
The roles of muscles that span a single joint (monoarticular) versus those that span two (biarticular) or more joints have been suggested to differ. Monoarticular muscles are argued to perform work at a joint, whereas biarticular muscles are argued to transfer energy while resisting moments across adjacent joints. To test these predictions, in vivo patterns of muscle activation, strain, and strain rate were compared using electromyography and sonomicrometry in two major elbow extensors, the long and lateral heads of the triceps brachii of goats (Capra hircus), across a range of speed (1-5 m s(-1)) and gait. Muscle recordings were synchronized to limb kinematics using high-speed digital video imaging (250 Hz). Measurements obtained from four goats (25-45 kg) showed that the monoarticular lateral head exhibited a stretch-shortening pattern (6.8+/-0.6% stretch and -10.6+/-2.7% shortening; mean+/-s.e.m. for all speeds and gaits) after being activated, which parallels the flexion-extension pattern of the elbow. By contrast, the biarticular long head shortened through most of stance (-16.4+/-3.4%), despite elbow flexion in the first half and shoulder extension in the last half of stance. The magnitude of elbow flexion and shoulder extension increased with increasing speed (ANCOVA, P<0.05 and P<0.001), as did the magnitude and rate of active stretch of fascicles in the lateral head (P<0.001 for both). In all individuals, shortening fascicle strain rates increased with speed in the long head (P<0.001), and, in three of the four individuals, strain magnitude increased. Few independent effects of gait were found. In contrast to its expected function, the biarticular long head appears to produce positive work throughout stance, whereas the monoarticular lateral head appears to absorb work at the elbow. The biarticular anatomy of the long head may mitigate increases in muscle strain with speed in this muscle, because strain magnitude in the second phase of stance (when the shoulder extends) decreased with speed (P<0.05).
跨越单个关节（单关节）的肌肉与跨越两个（双关节）或更多关节的肌肉的作用被认为有所不同。有人认为单关节肌肉在关节处做功，而双关节肌肉在抵抗相邻关节的力矩时传递能量。为了验证这些预测，利用肌电图和超声测量法，在一系列速度（1-5米/秒）和步态下，比较了山羊（Capra hircus）肱三头肌长头和外侧头这两块主要的肘部伸肌在体内的肌肉激活、应变和应变率模式。肌肉记录通过高速数字视频成像（250赫兹）与肢体运动学同步。从四只山羊（25-45千克）获得的测量结果表明，单关节的外侧头在被激活后呈现出拉伸-缩短模式（拉伸6.8±0.6%，缩短-10.6±2.7%；所有速度和步态的平均值±标准误），这与肘部的屈伸模式相似。相比之下，双关节的长头在大部分站立阶段都在缩短（-16.4±3.4%），尽管在站立的前半段肘部弯曲，后半段肩部伸展。肘部弯曲和肩部伸展的幅度随着速度的增加而增加（协方差分析，P<0.05和P<0.001），外侧头肌束的主动拉伸幅度和速率也如此（两者P<0.001）。在所有个体中，长头肌束缩短应变率随着速度增加（P<0.001），并且在四个个体中的三个个体中，应变幅度增加。几乎没有发现步态的独立影响。与其预期功能相反，双关节的长头在整个站立阶段似乎都在产生正功，而单关节的外侧头在肘部似乎在吸收功。长头的双关节解剖结构可能减轻了该肌肉中应变随速度的增加，因为站立第二阶段（当肩部伸展时）的应变幅度随着速度降低（P<0.05）。
