Hanchard N C, Williamson M, Caley R W, Cooper R G
School of Health Sciences, The Robert Gordon University, Aberdeen, Scotland, UK.
Clin Rehabil. 1998 Oct;12(5):413-27. doi: 10.1191/026921598671467836.
To investigate the validity and reliability of submaximal voltage stimulation for assessing the 'fresh' contractile properties of human tibialis anterior muscle (TA) and the efficacy of such stimulation in inducing and assessing high- and low-frequency fatigue.
(A) Contractile properties of fresh TA were assessed in six normal volunteers using multifrequency stimulation trains (comprising 2 seconds at each of 10, 20 and 50 Hz, arranged contiguously) over a range of submaximal voltages. (B) On three separate occasions, fatigue was induced in the TA of 10 normal volunteers by means of a 3-minute unbroken sequence of the described multifrequency stimulation trains, delivered at a 'standardized' submaximal voltage. This fatiguing protocol was preceded by discrete multifrequency stimulation trains, at the same standardized voltage, but followed by discrete multifrequency trains delivered over a range of submaximal voltages (which included the standardized voltage).
In experiment A the 10:50 Hz and 20:50 Hz force ratios were analysed for between-voltages variability using coefficients of variation (CVs), and for trends using Friedman tests and post-hoc Wilcoxon tests. In experiment B low-frequency fatigue was detected using 10:50 Hz and 20:50 Hz force ratios derived from the discrete multifrequency trains. High-frequency fatigue was calculated from the decline in high-frequency force which occurred during the fatiguing protocol itself. Each parameter was assessed for between-days repeatability using CVs.
In experiment A the 'fresh' 10:50 Hz force ratio was clearly unreliable at voltages which generated <10% of maximal voluntary contractile force (MVC) (CV< or =29.7%), but was reasonably reliable at voltages which generated 20-30% of MVC (CV < or = 11.5%; p = 0.847). The 'fresh' 20:50 Hz force ratio was,in contrast, extremely reliable throughout the tested voltage range (CV< or =5.8%; p = 0.636) in fresh muscle. In experiment B paired t-tests indicated that the fatiguing protocol induced significant high-frequency fatigue (p <0.0037) and low-frequency fatigue (p <0.0008 for 'fresh' versus 'fatigued' 10:50 Hz force ratio; p <0.0001 for 'fresh' versus 'fatigued' 20:50 Hz force ratio). In muscle thus fatigued, the 20:50 Hz force ratio was extremely reliable in the 20-33% of MVC range (CV < or =7.3%; p = 0.847). Between-days repeatability was poor for the 10:50 Hz force ratio in both fresh and fatigued muscle (CV < or =23.8 and 44.4% respectively), but was highly acceptable for both voluntary and stimulated fatigue indices and for the 20:50 Hz force ratio, the latter in both fresh and fatigued muscle.
These results confirm the validity and reliability of submaximal voltages in assessing contractile properties (including low-frequency fatiguability) and inducing fatigue of human TA.
研究次最大电压刺激评估人胫骨前肌（TA）“新鲜”收缩特性的有效性和可靠性，以及这种刺激在诱导和评估高频及低频疲劳方面的效果。
（A）在6名正常志愿者中，使用多频率刺激序列（包括在10、20和50Hz下各持续2秒，连续排列）在一系列次最大电压下评估新鲜TA的收缩特性。（B）在三个不同时间，通过以“标准化”次最大电压进行3分钟不间断的上述多频率刺激序列，诱导10名正常志愿者的TA疲劳。在这个疲劳方案之前，以相同的标准化电压进行离散的多频率刺激序列，但之后在一系列次最大电压（包括标准化电压）下进行离散的多频率刺激序列。
在实验A中，使用变异系数（CV）分析10:50Hz和20:50Hz力比在不同电压之间的变异性，并使用Friedman检验和事后Wilcoxon检验分析趋势。在实验B中，使用离散多频率刺激序列得出的10:50Hz和20:50Hz力比检测低频疲劳。高频疲劳通过疲劳方案本身期间高频力的下降来计算。使用CV评估每个参数在不同日期之间的重复性。
在实验A中，当电压产生的力小于最大自主收缩力（MVC）的10%时（CV≤29.7%），“新鲜”的10:50Hz力比明显不可靠，但当电压产生MVC的20 - 30%时则相当可靠（CV≤11.5%；p = 0.847）。相比之下，“新鲜”的20:50Hz力比在新鲜肌肉的整个测试电压范围内都极其可靠（CV≤5.8%；p = 0.636）。在实验B中，配对t检验表明疲劳方案诱导了显著的高频疲劳（p <0.0037）和低频疲劳（“新鲜”与“疲劳”的10:50Hz力比，p <0.0008；“新鲜”与“疲劳”的20:50Hz力比，p <0.0001）。在如此疲劳的肌肉中，20:50Hz力比在MVC的20 - 33%范围内极其可靠（CV≤7.3%；p = 0.847）。新鲜和疲劳肌肉中10:50Hz力比在不同日期之间的重复性都很差（分别为CV≤23.8%和44.4%），但自愿和刺激疲劳指数以及20:50Hz力比（新鲜和疲劳肌肉中的后者）的重复性都非常可接受。
这些结果证实了次最大电压在评估收缩特性（包括低频疲劳性）和诱导人TA疲劳方面的有效性和可靠性。
