Department of Integrative Biology, 4202 East Fowler Avenue, SCA 110, University of South Florida, Tampa, FL 33620, USA.
J Exp Biol. 2012 Jan 15;215(Pt 2):287-300. doi: 10.1242/jeb.063230.
The extrinsic limb muscles perform locomotor work and must adapt their activity to changes in gait and locomotor speed, which can alter the work performed by, and forces transmitted across, the proximal fulcra of the limbs where these muscles operate. We recorded electromyographic activity of 23 extrinsic forelimb and hindlimb muscles and one trunk muscle in dogs while they walked, trotted and galloped on a level treadmill. Muscle activity indicates that the basic functions of the extrinsic limb muscles - protraction, retraction and trunk support - are conserved among gaits. The forelimb retains its strut-like behavior in all gaits, as indicated by both the relative inactivity of the retractor muscles (e.g. the pectoralis profundus and the latissimus dorsi) during stance and the protractor muscles (e.g. the pectoralis superficialis and the omotransversarius) in the first half of stance. The hindlimb functions as a propulsive lever in all gaits, as revealed by the similar timing of activity of retractors (e.g. the biceps femoris and the gluteus medius) during stance. Excitation increased in many hindlimb muscles in the order walk-trot-gallop, consistent with greater propulsive impulses in faster gaits. Many forelimb muscles, in contrast, showed the greatest excitation at trot, in accord with a shorter limb oscillation period, greater locomotor work performed by the forelimb and presumably greater absorption of collisional energy.
外在肢体肌肉执行运动工作，必须适应步态和运动速度的变化，这些变化会改变肢体近端支点所承受的工作和力的传递。我们记录了狗在水平跑步机上行走、小跑和疾驰时 23 块外在前肢和后肢肌肉以及一块躯干肌肉的肌电图活动。肌肉活动表明，外在肢体肌肉的基本功能——伸展、回缩和躯干支撑——在不同步态中是保守的。前肢在所有步态中都保持着类似于支柱的行为，这表现在支撑期回缩肌（如胸深肌和背阔肌）相对不活跃，以及支撑期前伸肌（如胸浅肌和多关节肌）在前半段的活跃。后肢在所有步态中都作为推进杠杆，这反映在支撑期回缩肌（如股二头肌和臀中肌）的活动时间相似。随着步态的加快，许多后肢肌肉的兴奋程度增加，这与更大的推进冲量一致。相比之下，许多前肢肌肉在小跑时表现出最大的兴奋，这与较短的肢体摆动周期、前肢完成的更大的运动工作以及可能更大的碰撞能量吸收一致。
