Raikova R, Pogrzebna M, Drzymała H, Celichowski J, Aladjov H
Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Sofia 1113, Acad. G. Bonchev St., Bl. 105, Bulgaria.
J Electromyogr Kinesiol. 2008 Oct;18(5):741-51. doi: 10.1016/j.jelekin.2007.02.010. Epub 2007 Apr 6.
Stimulation of motor units (MUs) with repeated pulses evokes tetanic contractions, which consist of overlapping mechanical responses. The summation of these responses into tetanus is a nonlinear process due to the dynamic changes in the amplitudes and time parameters of the successive components. In order to study these changes, two MUs (one fast and one slow) of rat medial gastrocnemius muscle were stimulated with a progressively increasing number of pulses, from one (i=1) to sixteen (i=16) at a frequency of 15 Hz for the slow MU and 60 Hz for the fast MU. The individual responses were calculated by subtracting the (i)th from the (i+1)th tetanus recording. The contractions obtained following subtraction were modeled using a novel 6-parameter analytical function. The main conclusions of this study are (1) the newly presented analytical function is able to precisely describe the variable shape of all subtracted experimental contractions; (2) the shapes of successive contractions are variable and the subtracted contractions differ from the individual twitches; (3) as the pulse number increases, the parameters of the subtracted contractions change in a different manner for the slow and fast MUs: for the slow MU, the maximal forces and the time parameters increase considerably up to the 4th response, after which they remain nearly constant or show only a slight increase; for the fast MU, the maximal forces and durations also increase, whereas the remaining time parameters initially increase and then maintain a constant level or decrease, which explains the sag phenomenon visible in the unfused tetanus of fast MUs.
用重复脉冲刺激运动单位（MUs）会诱发强直收缩，强直收缩由重叠的机械反应组成。由于连续成分的幅度和时间参数的动态变化，这些反应叠加成强直是一个非线性过程。为了研究这些变化，以逐渐增加的脉冲数刺激大鼠内侧腓肠肌的两个运动单位（一个快肌运动单位和一个慢肌运动单位），慢肌运动单位的刺激频率为15Hz，快肌运动单位为60Hz，脉冲数从1个（i = 1）增加到16个（i = 16）。通过从第（i + 1）次强直记录中减去第（i）次强直记录来计算个体反应。使用一种新颖的六参数分析函数对相减后得到的收缩进行建模。本研究的主要结论是：（1）新提出的分析函数能够精确描述所有相减后的实验性收缩的可变形状；（2）连续收缩的形状是可变的，相减后的收缩与单个抽搐不同；（3）随着脉冲数增加，慢肌运动单位和快肌运动单位相减后收缩的参数变化方式不同：对于慢肌运动单位，最大力和时间参数在第4次反应前大幅增加，之后它们几乎保持不变或仅略有增加；对于快肌运动单位，最大力和持续时间也增加，而其余时间参数最初增加，然后保持恒定水平或下降，这解释了在快肌运动单位的不完全强直中可见的松弛现象。
