McNulty P A, Cresswell A G
Prince of Wales Medical Research Institute and University of New South Wales, Barker Street, Randwick, NSW 2031, Australia.
J Electromyogr Kinesiol. 2004 Jun;14(3):369-77. doi: 10.1016/j.jelekin.2003.10.003.
We investigated the recruitment behaviour of low threshold motor units in flexor digitorum superficialis by altering two biomechanical constraints: the load against which the muscle worked and the initial muscle length. The load was increased using isotonic (low load), loaded dynamic (intermediate load) and isometric (high load) contractions in two studies. The initial muscle position reflected resting muscle length in series A, and a longer length with digit III fully extended in series B. Intramuscular EMG was recorded from 48 single motor units in 10 experiments on five healthy subjects, 21 units in series A and 27 in series B, while subjects performed ramp up, hold and ramp down contractions. Increasing the load on the muscle decreased the force, displacement and firing rate of single motor units at recruitment at shorter muscle lengths (P<0.001, dependent t-test). At longer muscle lengths this recruitment pattern was observed between loaded dynamic and isotonic contractions, but not between isometric and loaded dynamic contractions. Thus, the recruitment properties of single motor units in human flexor digitorum superficialis are sensitive to changes in both imposed external loads and the initial length of the muscle.
我们通过改变两个生物力学限制因素，即肌肉工作时所对抗的负荷以及肌肉的初始长度，来研究指浅屈肌中低阈值运动单位的募集行为。在两项研究中，分别采用等张收缩（低负荷）、加负荷动态收缩（中等负荷）和等长收缩（高负荷）来增加负荷。在A组中，初始肌肉位置反映静息肌肉长度；在B组中，当第三指完全伸展时，初始肌肉位置反映更长的长度。在对5名健康受试者进行的10次实验中，从48个单运动单位记录肌内肌电图，其中A组21个单位，B组27个单位，同时受试者进行逐渐增加负荷、保持和逐渐降低负荷的收缩。在较短肌肉长度下，增加肌肉负荷会降低单运动单位在募集时的力量、位移和放电频率（P<0.001，配对t检验）。在较长肌肉长度下，这种募集模式在加负荷动态收缩和等张收缩之间可以观察到，但在等长收缩和加负荷动态收缩之间未观察到。因此，人类指浅屈肌中单运动单位的募集特性对施加的外部负荷和肌肉初始长度的变化均敏感。
