Neurophysiology of Movement Laboratory, Carlson 202G 354 UCB, Department of Integrative Physiology, University of Colorado, Boulder, CO 80309-0354, USA.
J Neurophysiol. 2011 Feb;105(2):571-81. doi: 10.1152/jn.00841.2010. Epub 2010 Dec 15.
The purpose of this study was to compare the discharge characteristics of motor units recruited during an isometric contraction that was sustained with the elbow flexor muscles by older adults at target forces that were less than the recruitment threshold force of each isolated motor unit. The discharge times of 27 single motor units were recorded from the biceps brachii in 11 old adults (78.8 ± 5.9 yr). The target force was set at either a relatively small (6.6 ± 3.7% maximum) or large (11.4 ± 4.5% maximum) difference below the recruitment threshold force and the contraction was sustained until the motor unit was recruited and discharged action potentials for about 60 s. The time to recruitment was longer for the large target-force difference (P = 0.001). At recruitment, the motor units discharged repetitively for both target-force differences, which contrasts with data from young adults when motor units discharged intermittently at recruitment for the large difference between recruitment threshold force and target force. The coefficient of variation (CV) for the first five interspike intervals (ISIs) increased from the small (18.7 ± 7.9) to large difference (35.0 ± 10.2%, P = 0.008) for the young adults, but did not differ for the two target force differences for the old adults (26.3 ± 14.7 to 24.0 ± 13.1%, P = 0.610). When analyzed across the discharge duration, the average CV for the ISI decreased similarly for the two target-force differences (P = 0.618) in old adults. These findings contrast with those of young adults and indicate that the integration of synaptic input during sustained contractions differs between young and old adults.
这项研究的目的是比较在等长收缩期间募集的运动单位的放电特征，这些运动单位由老年受试者在低于每个分离运动单位募集阈值力的目标力下募集。从 11 名老年受试者（78.8 ± 5.9 岁）的肱二头肌中记录了 27 个单运动单位的放电时间。目标力设定为募集阈值力以下的相对较小（6.6 ± 3.7%最大）或较大（11.4 ± 4.5%最大）差值，收缩持续至运动单位募集并放电动作电位约 60 秒。大目标力差值时的募集时间更长（P = 0.001）。在募集时，运动单位对于两种目标力差值都重复放电，这与年轻人的数据形成对比，年轻人在募集阈值力与目标力之间的差值较大时，运动单位间歇性放电。年轻人的第一个五个峰间隔（ISI）的变异系数（CV）从小（18.7 ± 7.9）到大差异（35.0 ± 10.2%，P = 0.008）增加，但老年人的两个目标力差值之间没有差异（26.3 ± 14.7 到 24.0 ± 13.1%，P = 0.610）。当在放电持续时间上进行分析时，老年人的两个目标力差值的平均 ISI 变异系数（CV）也相似下降（P = 0.618）。这些发现与年轻人的发现形成对比，表明在持续收缩期间，突触输入的整合在年轻人和老年人之间存在差异。
