Pasquet Benjamin, Carpentier Alain, Duchateau Jacques
Laboratory of Applied Biology, Université Libre de Bruxelles, 28 avenue P. Héger, CP 168, 1000 Brussels, Belgium.
J Neurophysiol. 2005 Nov;94(5):3126-33. doi: 10.1152/jn.00537.2005. Epub 2005 Jul 13.
This study examines the effect of fascicle length change on motor-unit recruitment and discharge rate in the human tibialis anterior (TA) during isometric contractions of various intensities. The torque produced during dorsiflexion and the surface and intramuscular electromyograms (EMGs) from the TA were recorded in eight subjects. The behavior of the same motor unit (n = 59) was compared at two ankle joint angles (+10 and -10 degrees around the ankle neutral position). Muscle fascicle length of the TA was measured noninvasively using ultrasonography recordings. When the ankle angle was moved from 10 degrees plantarflexion to 10 degrees dorsiflexion, the torque produced during maximal voluntary contraction (MVC) was significantly reduced [35.2 +/- 3.3 vs. 44.3 +/- 4.2 (SD) Nm; P < 0.001] and the average surface EMG increased (0.47 +/- 0.08 vs. 0.43 +/- 0.06 mV; P < 0.05). At reduced ankle joint angle, muscle fascicle length declined by 12.7% (P < 0.01) at rest and by 18.9% (P < 0.001) during MVC. Motor units were activated at a lower recruitment threshold for short compared with long muscle fascicle length, either when expressed in absolute values (2.1 +/- 2.5 vs. 3.6 +/- 3.7 Nm; P < 0.001) or relative to their respective MVC (5.2 +/- 6.1 vs. 8.8 +/- 9.0%). Higher discharge rate and additional motor-unit recruitment were observed at a given absolute or relative torque when muscle fascicles were shortened. However, the data indicate that increased rate coding was mainly present at low torque level (<10% MVC), when the muscle-tendon complex was compliant, whereas recruitment of additional motor units played a dominant role at higher torque level and decreased compliance (10-35% MVC). Taken together, the results suggest that the central command is modulated by the afferent proprioceptive information during submaximal contractions performed at different muscle fascicle lengths.
本研究考察了在不同强度等长收缩过程中，人体胫骨前肌（TA）肌束长度变化对运动单位募集和放电频率的影响。记录了8名受试者在背屈过程中产生的扭矩以及TA的表面肌电图和肌内肌电图（EMG）。在两个踝关节角度（围绕踝关节中立位置的+10度和 -10度）比较了同一运动单位（n = 59）的行为。使用超声记录非侵入性测量TA的肌肉肌束长度。当踝关节角度从跖屈10度移动到背屈10度时，最大自主收缩（MVC）过程中产生的扭矩显著降低[35.2 +/- 3.3对44.3 +/- 4.2（标准差）Nm；P < 0.001]，平均表面EMG增加（0.47 +/- 0.08对0.43 +/- 0.06 mV；P < 0.05）。在踝关节角度减小的情况下，静息时肌肉肌束长度下降12.7%（P < 0.01），MVC期间下降18.9%（P < 0.001）。与长肌束长度相比，短肌束长度时运动单位在较低的募集阈值被激活，无论是以绝对值表示（2.1 +/- 2.5对3.6 +/- 3.7 Nm；P < 0.001）还是相对于各自的MVC（5.2 +/- 6.1对8.8 +/- 9.0%）。当肌肉肌束缩短时，在给定的绝对或相对扭矩下观察到更高的放电频率和额外的运动单位募集。然而，数据表明，增加的频率编码主要出现在低扭矩水平（<10% MVC），此时肌腱复合体具有顺应性，而额外运动单位的募集在较高扭矩水平和较低顺应性（10 - 35% MVC）时起主导作用。综上所述，结果表明在不同肌肉肌束长度下进行次最大收缩时，中枢指令受传入的本体感觉信息调制。
