Biomechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, Kansas, USA.
J Strength Cond Res. 2013 Aug;27(8):2314-8. doi: 10.1519/JSC.0b013e318277d64c.
The purpose of this study was to examine the effects of a doublet stimulus evoked during isometric submaximal contractions on the electromechanical delay (EMD). Twenty-three healthy individuals performed isometric step contractions ranging from 10 to 70% maximal voluntary contraction (MVC) with a doublet stimulus applied during the contractions. A 2-way repeated-measures analysis of variance (gender [male vs. female] × contraction intensity [10% vs. 20% vs. 30% vs. 40% vs. 50% vs. 60% vs. 70% MVC]) was used to analyze the EMD. The EMD at 10% was significantly less than at 30% (p = 0.022), 40% (p = 0.044), 50% (p = 0.012), 60% (p = 0.041), and 70% MVC (p < 0.001). In addition, the EMD at 70% MVC was significantly higher than at 20% (p = 0.002), 30% (p = 0.006), 40% (p = 0.009), and 50% MVC (p = 0.021). The EMD is the time difference between muscle activation and the onset of muscle force production, with the stretching of the series elastic component (SEC) as the major contributor. A doublet stimulus applied during an isometric contraction minimizes the effects of the SEC during the interpolated twitch technique. Therefore, when the SEC is minimized, the EMD may be lengthened because of mechanisms associated with the excitation-contraction coupling at higher contraction intensities. The EMD measurement, produced with a doublet stimulus, could potentially be a useful tool to examine the effects of fatigue, exercise, stretching, and so on, on the excitation-contraction coupling during various force levels. However, future research is needed to further elucidate the mechanisms that result in a lengthening of the EMD under these conditions.
本研究旨在探讨在等长次最大收缩期间给予双刺激对机电延迟（EMD）的影响。23 名健康个体进行了从 10%到 70%最大随意收缩（MVC）的等长台阶收缩，在收缩期间给予双刺激。采用双因素重复测量方差分析（性别[男性与女性]×收缩强度[10%、20%、30%、40%、50%、60%、70% MVC]）分析 EMD。10%的 EMD 明显小于 30%（p = 0.022）、40%（p = 0.044）、50%（p = 0.012）、60%（p = 0.041）和 70% MVC（p < 0.001）。此外，70% MVC 的 EMD 明显高于 20%（p = 0.002）、30%（p = 0.006）、40%（p = 0.009）和 50% MVC（p = 0.021）。EMD 是肌肉激活和肌肉力产生之间的时间差，串联弹性成分（SEC）的拉伸是主要贡献者。在等长收缩期间施加双刺激可在插值 twitch 技术期间最小化 SEC 的影响。因此，当 SEC 最小时，由于与较高收缩强度下的兴奋-收缩偶联相关的机制，EMD 可能会延长。在双刺激下产生的 EMD 测量值可能是一种有用的工具，可以检查疲劳、运动、拉伸等因素在各种力水平下对兴奋-收缩偶联的影响。然而，需要进一步的研究来阐明在这些条件下导致 EMD 延长的机制。
