Potvin J R
Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada.
J Appl Physiol (1985). 1997 Jan;82(1):144-51. doi: 10.1152/jappl.1997.82.1.144.
Fifteen male subjects performed a repetitive elbow flexion/extension task with a 7-kg mass until exhaustion. Average joint angle, angular velocity, and biceps brachii surface electromyographic (EMG) amplitude (aEMG) and mean power frequency (MPF) were calculated with each consecutive 250-ms segment of data during the entire trial. Data were separated into concentric or eccentric phases and into seven 20 degree-ranges from 0 to 140 degrees of elbow flexion. A regression analysis was used to estimate the rested and fatigued aEMG and MPF values. aEMG values were expressed as a percentage of amplitudes from maximum voluntary contractions (MVC). Under rested dynamic conditions, the average concentric aEMG amplitude was 10% MVC higher than average eccentric values. Rested MPF values were similar for concentric and eccentric phases, although values increased approximately 20 Hz from the most extended to flexed joint angles. Fatigue resulted in an average increase in concentric and eccentric aEMG of 35 and 10% MVC, respectively. The largest concentric aEMG increases (up to 58% MVC) were observed at higher joint velocities, whereas eccentric increases appeared to be related to decreases in velocity. Fatigue had a similar effect on MPF during both concentric and eccentric phases. Larger MPF decreases were observed at shorter muscle lengths such that values within each angle range were very similar by the end of the trial. It was hypothesized that this finding may reflect a biological minimum in conduction velocity before propagation failure occurs.
15名男性受试者进行了一项重复的肘部屈伸任务，负荷为7千克，直至疲劳。在整个试验过程中，对每连续250毫秒的数据段计算平均关节角度、角速度、肱二头肌表面肌电图（EMG）幅度（aEMG）和平均功率频率（MPF）。数据被分为向心或离心阶段，并分为从肘部屈曲0度到140度的七个20度范围。采用回归分析来估计静息和疲劳状态下的aEMG和MPF值。aEMG值以最大自主收缩（MVC）幅度的百分比表示。在静息动态条件下，平均向心aEMG幅度比平均离心值高10%MVC。静息时的MPF值在向心和离心阶段相似，尽管从最伸展到屈曲的关节角度，值增加了约20赫兹。疲劳导致向心和离心aEMG分别平均增加35%和10%MVC。在较高关节速度下观察到最大的向心aEMG增加（高达58%MVC），而离心增加似乎与速度降低有关。疲劳在向心和离心阶段对MPF有类似影响。在较短肌肉长度时观察到较大的MPF降低，以至于在试验结束时每个角度范围内的值非常相似。据推测，这一发现可能反映了在传导失败发生之前传导速度的生物学最小值。
