Dimitrov George V, Arabadzhiev Todor I, Mileva Katya N, Bowtell Joanna L, Crichton Nicola, Dimitrova Nonna A
Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Med Sci Sports Exerc. 2006 Nov;38(11):1971-9. doi: 10.1249/01.mss.0000233794.31659.6d.
The aim of the present study was to test the applicability and sensitivity of new electromyography (EMG) spectral indices in assessing peripheral muscle fatigue during dynamic knee-extension exercise.
Seven subjects completed 10 sets of 15 repetitions of right knee-extension exercise lifting 50% of their one-repetition maximum. Torque (T), knee-joint angle, and the interference EMG of rectus femoris muscle were recorded simultaneously. Maximal voluntary isometric contraction (MVC) was tested before and after exercise. Median spectral frequency (Fmed) and new spectral indices of muscle fatigue (FInsmk) were calculated for each repetition.
The rate and range of FInsmk- and Fmed-relative changes against the first repetition of the corresponding set increased gradually across successive repetitions within the set, reflecting accumulation of peripheral muscle fatigue. The maximal change of FInsmk observed in the present experiment was approximately eightfold, whereas that of Fmed was only 32%. Significant between-subject variability in the range of FInsmk changes (P < 0.0001) was found, so a hierarchical cluster analysis of muscle fatigue indices was conducted. Three distinct subgroups of subjects were identified: high (N = 1, FInsmk change > 400%), medium (N = 4, 200% < FInsmk change < 400%), and low (N = 2, FInsmk change < 200%) muscle fatigability. The changes in muscle performance during (last vs first repetition peak T, P = 0.03) and after (post- vs preexercise MVC, P = 0.012) exercise were significantly different between clusters (one-way ANOVA). The rate of fatigue development was also significantly different between clusters (linear regression analysis of Fmed and FInsmk changes).
The new spectral indices are a valid and reliable tool for assessment of muscle fatigability irrespective of EMG signal variability caused by dynamic muscle contractions, and these indices are more sensitive than those traditionally used.
本研究旨在测试新的肌电图（EMG）频谱指标在评估动态伸膝运动期间外周肌肉疲劳方面的适用性和敏感性。
7名受试者以其一次重复最大值的50%完成10组，每组15次的右膝伸展运动。同时记录扭矩（T）、膝关节角度和股直肌的干扰肌电图。在运动前后测试最大自主等长收缩（MVC）。计算每组每次重复的中位频谱频率（Fmed）和新的肌肉疲劳频谱指标（FInsmk）。
在相应组的连续重复中，FInsmk和Fmed相对于第一次重复的相对变化率和范围逐渐增加，反映了外周肌肉疲劳的积累。在本实验中观察到的FInsmk的最大变化约为8倍，而Fmed仅为32%。发现FInsmk变化范围存在显著的受试者间变异性（P < 0.0001），因此对肌肉疲劳指标进行了分层聚类分析。确定了三个不同的受试者亚组：高肌肉疲劳性（N = 1，FInsmk变化> 400%）、中肌肉疲劳性（N = 4，200% < FInsmk变化< 400%）和低肌肉疲劳性（N = 2，FInsmk变化< 200%）。各聚类之间运动期间（最后一次与第一次重复峰值T，P = 0.03）和运动后（运动后与运动前MVC，P = 0.012）肌肉性能的变化有显著差异（单因素方差分析）。各聚类之间疲劳发展速率也有显著差异（Fmed和FInsmk变化的线性回归分析）。
新的频谱指标是评估肌肉疲劳性的有效且可靠的工具，无论动态肌肉收缩引起的EMG信号变异性如何，并且这些指标比传统使用的指标更敏感。
