BALLISTIC CONTRACTIONS IN MAN - CHARACTERISTIC RECRUITMENT PATTERN OF SINGLE MOTOR UNITS OF TIBIALIS ANTERIOR MUSCLE
BALLISTIC CONTRACTIONS IN MAN - CHARACTERISTIC RECRUITMENT PATTERN OF SINGLE MOTOR UNITS OF TIBIALIS ANTERIOR MUSCLE
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DOI：
10.1113/jphysiol.1977.sp011689
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发表时间：
1977-01-01
影响因子：
5.5
通讯作者：
GODAUX, E
中科院分区：
文献类型：
--
作者：
DESMEDT, JE;GODAUX, E
用高选择性电极记录成年人完整胫骨前肌的单个运动单位，对不同峰值力和不同力发展速率下的自主等长收缩过程中的放电模式进行了详细的参数分析。在斜坡力的平滑跟踪过程中，从给定肌肉部位记录的不同运动单元以一致的顺序被招募，当肌肉产生一定水平的力时，每个单元变得活跃。在这种缓慢的斜坡收缩中，一些单位的阈值超过8公斤。相比之下，在不到0.15秒的时间内达到12 kg峰值力的快速弹道收缩中，相同的运动单元在瞬时爆发中放电，这在很大程度上先于肌肉力量的产生。在缓慢跟踪斜坡收缩中，单个运动单元的瞬时频率最初相当低（5-15/s），并且随着斜坡力的增加而增加。相比之下，在（强）弹道收缩中，相同的单位在爆发早期以异常高的瞬时频率（60-120/s）放电，此后放电频率降低。先前未知的模式出现了弹道收缩的特征，并且在仅0.4 s内达到12 kg的快速跟踪斜坡收缩中也没有发现。在强烈弹道收缩的早期爆发中，激活的不同运动单位的电位在几毫秒的间隔内相当拥挤，对不同运动单位的等级激活的观察并没有为分析单位的募集顺序提供可靠的数据弹道收缩。提出了一种估算单运动单元冲击力阈值的新方法。当进行一系列峰值力范围为0.05-12 kg的快速弹道收缩时，只有当弹道峰值力超过某一可再现值时，任何给定的运动单元才开始活动。基于这些弹道力阈值的招募顺序的详细分析表明，它几乎与缓慢跟踪斜坡收缩中相同单位的招募顺序相同（相关性= 0.95）。弹道性收缩的强度分为两个等级，一个是在较强的收缩中招募了额外的运动单位，另一个是它们发射速率的增加。并对这些级配机理进行了探讨。
Single motor units were recorded with highly selective electrodes from intact tibialis anterior muscle in the adult man. A detailed parametric analysis was made of the discharge patterns during voluntary isometric contractions of different peak forces carried out at various rates of force development. During the smooth tracking of a ramp force, the different motor units recorded from a given muscle site were recruited in a consistent order, each unit becoming active when the muscle developed a certain level of force. The threshold of some of the units in such slow ramp contractions exceeded 8 kg. By contrast, in brisk ballistic contractions reaching a peak force of 12 kg in less than 0.15 s, the same motor units discharged in a transient burst which largely preceded the muscle force production. In slow tracking ramp contractions, the instantaneous frequency of single motor units was initially rather low (5-15/s) and it increased as the ramp force augmented. By contrast, in (strong) ballistic contractions, the same units discharged at an unusually high instantaneous frequency (60-120/s) early in the burst and the firing frequency decreased thereafter. A previous unknown pattern appeared characteristic of ballistic contractions and it was not found in even fast tracking ramp contractions achieving 12 kg in only 0.4 s. The potentials of the different motor units activated were rather crowded at intervals of a few milliseconds in the early burst of a strong ballistic contraction and observations on the rank activation of the different motor units did not provide reliable data for the analysis of the recruitment order of units in ballistic contractions. A new method was described for estimating ballistic force threshold of single motor units. When a large series of brisk ballistic contractions with peak forces ranging from 0.05-12 kg was carried out any given motor unit only became active when the ballistic peak force exceeded a certain reproducible value. A detailed analysis of the recruitment order based on these ballistic force thresholds showed it to be virtually identical to the recruitment order of the same units in slow tracking ramp contractions (correlation = 0.95). Ballistic contractions are graded in force both by the recruitment of additional motor units in stronger contractions, and by an increase in their rate of firing. These gradation mechanisms were discussed.