Baudry Stéphane, Duchateau Jacques
Laboratory of Applied Biology, Université Libre de Bruxelles, 28 avenue P, Héger, CP 168, 1000 Brussels, Belgium.
Muscle Nerve. 2004 Sep;30(3):328-36. doi: 10.1002/mus.20101.
The mechanical performance of a muscle can be enhanced by preceding contractile activity, such as occurs with postactivation potentiation. To investigate whether the type of contraction influences the extent of potentiation, the effects of 6-s maximal isometric (ISO), concentric (CON), and eccentric (ECC) maximal voluntary contractions (MVC) on the muscle twitch were compared in the tibialis anterior of nine subjects. The study also examined the effect of postactivation potentiation on the force evoked by the second (C2) and third (C3) responses of two-pulse (PT2) and three-pulse (PT3) trains that were delivered at a 10-ms interpulse interval. The results showed that immediately after the conditioning MVC, twitch torque (Pt) and its maximal rate of torque development (+dPt/dt) and relaxation (-dPt/dt) were significantly enhanced, without any change in contraction time (CT), half-relaxation time ((1/2)RT), and compound muscle action potential (M wave). The extent of Pt potentiation was similar for all MVC modalities, and the mean maximal values ranged from 150% to 180%. Furthermore, postactivation potentiation was greater for the single pulse compared with PT2 and PT3 responses. All parameters returned to initial values within 7-10 min. Although Pt (or C1) was potentiated more than was C2 and C3, its decline over time was proportionally more rapid than those for C2 and C3. We conclude that postactivation potentiation was not related to the type of conditioning MVC under these experimental conditions. The observation that postactivation potentiation increased C1 more than C2 and C3 indicates that a saturation process limits the extent of potentiation during the summation of successive responses to a train of stimuli. These results have practical application in the design of functional electrical stimulation protocols.
肌肉的机械性能可通过先前的收缩活动得到增强，比如在激活后增强效应中所发生的那样。为了研究收缩类型是否会影响增强程度，在9名受试者的胫骨前肌中比较了6秒最大等长收缩（ISO）、向心收缩（CON）和离心收缩（ECC）最大自主收缩（MVC）对肌肉抽搐的影响。该研究还考察了激活后增强效应对于在10毫秒脉冲间隔下施加的双脉冲（PT2）和三脉冲（PT3）序列的第二个（C2）和第三个（C3）反应所诱发力量的影响。结果显示，在条件性MVC之后即刻，抽搐扭矩（Pt）及其最大扭矩发展速率（+dPt/dt）和松弛速率（-dPt/dt）显著增强，而收缩时间（CT）、半松弛时间（(1/2)RT）和复合肌肉动作电位（M波）没有任何变化。所有MVC模式下Pt增强的程度相似，平均最大值在150%至180%之间。此外，与PT2和PT3反应相比，单脉冲的激活后增强效应更大。所有参数在7至10分钟内恢复到初始值。尽管Pt（或C1）比C2和C3增强得更多，但它随时间的下降比C2和C3成比例地更快。我们得出结论，在这些实验条件下，激活后增强效应与条件性MVC的类型无关。激活后增强效应使C1比C2和C3增加得更多这一观察结果表明，在对一串刺激的连续反应总和期间，一个饱和过程限制了增强的程度。这些结果在功能性电刺激方案的设计中有实际应用。
