School of Rehabilitation, Faculty of Medicine, University of Montreal, Montreal, Quebec, Canada; Research Centre, Montreal Rehabilitation Institute, 6300 Darlington Av., Montreal, Quebec, Canada.
J Electromyogr Kinesiol. 1993;3(4):205-13. doi: 10.1016/1050-6411(93)90009-L.
Different behaviours of the EMG power spectrum across increasing force levels have been reported for the masseter muscle. A factor that could explain these different behaviours may be the type of contraction used, as was recently shown for certain upper limb muscles(5). The purpose of this study was to compare, between two types of isometric contractions, the behaviour of EMG power spectrum statistics (median frequency (MF) and mean power frequency (MPF)) obtained across increasing force levels. Ten women exerted, while biting in the intercuspal position, three 5 s ramp contractions that increased linearly from 0 to 100% of the maximal voluntary contraction (MVC). They also completed three step contractions (constant EMG amplitude) at each of the following levels: 20, 40, 60 and 80% MVC. EMG signals from the masseter muscle were recorded with miniature surface electrodes. The RMS, as well as the MPF and MF of the power spectrum were calculated at 20, 40, 60 and 80% MVC for each type of contraction. As expected, the RMS values showed similar increases with increasing levels of effort for both types of contractions. Different behaviours for both MPF (contraction(∗)force interaction, ANOVA, P<0.05) and MF (contraction(∗)force interaction, ANOVA, P>0.05) across increasing levels of effort were found between the two types of contraction. The use of step contractions gave rise to a decrease of both MPF and MF with increasing force, while the use of ramp contractions gave rise to an increase in both statistics up to at least 40% MVC followed by a decrease at higher force levels. These findings suggest that the type of contraction used does influence the behaviour of the spectral statistics across increasing force levels and that this could explain the differences obtained in previous studies for the masseter muscle.
不同的力水平下，咀嚼肌肌电图（EMG）功率谱的行为已经有报道。这种不同行为的一个可能的解释因素可能是所使用的收缩类型，正如最近某些上肢肌肉的研究所示（5）。本研究的目的是比较两种等长收缩类型，即在力逐渐增加的过程中，获得的 EMG 功率谱统计数据（中值频率（MF）和平均功率频率（MPF））的行为。十名女性在牙尖交错位咬住时，进行了三次 5 秒斜坡收缩，力从 0 线性增加到最大自主收缩（MVC）的 100%。她们还在以下每个水平完成了三次阶跃收缩（恒定 EMG 幅度）：20%、40%、60%和 80% MVC。使用微型表面电极记录咀嚼肌的 EMG 信号。对于每种类型的收缩，在 20%、40%、60%和 80% MVC 时，计算 RMS 以及功率谱的 MPF 和 MF。正如预期的那样，对于两种类型的收缩，RMS 值随着努力水平的增加而呈现出相似的增加。对于两种类型的收缩，在力逐渐增加的过程中，MPF（收缩（∗）力相互作用，ANOVA，P<0.05）和 MF（收缩（∗）力相互作用，ANOVA，P>0.05）都表现出不同的行为。使用阶跃收缩会导致 MPF 和 MF 随着力的增加而降低，而使用斜坡收缩会导致这两种统计数据增加，至少在 40% MVC 之前，然后在更高的力水平下降低。这些发现表明，所使用的收缩类型确实会影响在力逐渐增加的过程中光谱统计数据的行为，这可以解释以前在咀嚼肌研究中获得的差异。
