Christie Anita, Kamen Gary
Department of Kinesiology, Totman Building, University of Massachusetts, Amherst, MA 01003, United States.
J Electromyogr Kinesiol. 2009 Aug;19(4):543-52. doi: 10.1016/j.jelekin.2008.03.005. Epub 2008 Apr 29.
The purpose of this study was to investigate changes in motor unit firing behavior during prolonged contractions in young and older adults. Motor unit activity was recorded from the tibialis anterior of 16 subjects (8 young and 8 older), while they performed isometric dorsiflexion at 50% MVC until task failure. Mean motor unit firing rate, the standard deviation (SD), and coefficient of variation (CV) of the interspike intervals, and number of doublet discharges were calculated for a total of 52 motor units, tracked for an average of 92.9+/-68.6s. There was no age-related difference in the time to task failure. A modest decline in firing rate was observed in 71% of the motor units, with no significant age-related difference. The SD and CV of the interspike interval had a positive slope in 65% and 69% of the motor units, respectively, with no significant age-related differences. The number of doublet discharges remained stable throughout the contraction. Both groups exhibited motor unit dropout (discharge cessation) during the contraction. Thus, a fatiguing task producing modest changes in firing rate in young and older adults is accompanied by an appreciable increase in firing rate variability. The incidence of doublet discharges is not increased during fatiguing contractions.
本研究的目的是调查年轻人和老年人在长时间收缩过程中运动单位放电行为的变化。记录了16名受试者（8名年轻人和8名老年人）胫骨前肌的运动单位活动，他们以50%最大随意收缩力进行等长背屈，直至任务失败。对总共52个运动单位计算了平均运动单位放电率、峰间期的标准差（SD）和变异系数（CV）以及成对放电次数，这些运动单位平均跟踪了92.9±68.6秒。任务失败时间在年龄上没有差异。71%的运动单位放电率出现适度下降，在年龄上没有显著差异。分别有65%和69%的运动单位峰间期的SD和CV呈正斜率，在年龄上没有显著差异。成对放电次数在整个收缩过程中保持稳定。两组在收缩过程中均出现运动单位丢失（放电停止）。因此，一项使年轻人和老年人放电率产生适度变化的疲劳任务伴随着放电率变异性的显著增加。在疲劳收缩过程中，成对放电的发生率没有增加。
