Birmingham T B, Kramer J F, Speechley M, Chesworth B M, MacDermid J
School of Physical Therapy, Elborn College, University of Western Ontario, London, Canada.
Ergonomics. 1998 Jun;41(6):853-63. doi: 10.1080/001401398186685.
Although the use of measures of strength variability as a means of judging sincerity of effort is becoming common practice, the accuracy of doing so has been questioned. Coefficient of variation (CV) cut-off points, indicating the upper limit of variability for repeated maximal efforts, are routinely used to identify workers providing submaximal efforts during various strength tests. However, the stability of the CV itself has not been considered when comparing an individual's observed CV score to these cut-off points. The purpose of the present study was to examine the day-to-day variability of the CV calculated from maximal isokinetic knee extension efforts, and to describe how this measurement error affects the accuracy of the CV as a distinguishing criterion between maximal and submaximal efforts. Thirty-one healthy males (mean age 25 +/- 4.5 years) completed three maximal and three submaximal isokinetic knee extension efforts on two separate occasions. Although submaximal CVs were significantly greater than maximal CVs (15.6 versus 3.7%; p < 0.01), there was considerable overlap between submaximal and maximal CV frequency distributions. More importantly, an individual observed CV could vary +/- 3.1% as a result of day-to-day variation or measurement error. This range in possible CV scores should be considered when comparing an individual's score to proposed cut-off points. Since individual CVs vary considerably from day-to-day, and since precise cut-off values distinguishing between maximal and submaximal conditions cannot be identified, CV scores must be interpreted cautiously, and the potential errors in relying extensively on this approach to identifying insincere efforts should be recognised.
尽管将力量变异性测量作为判断努力程度真实性的一种手段的做法正变得越来越普遍，但这样做的准确性却受到了质疑。变异系数（CV）截止点用于指示重复最大努力时变异性的上限，在各种力量测试中经常被用来识别付出次最大努力的工人。然而，在将个体观察到的CV分数与这些截止点进行比较时，CV本身的稳定性却未被考虑。本研究的目的是检验由最大等速膝关节伸展努力计算得出的CV的每日变异性，并描述这种测量误差如何影响CV作为区分最大努力和次最大努力的判别标准的准确性。31名健康男性（平均年龄25±4.5岁）在两个不同的场合分别完成了三次最大努力和三次次最大努力的等速膝关节伸展。尽管次最大努力时的CV显著大于最大努力时的CV（15.6%对3.7%；p<0.01），但次最大努力和最大努力的CV频率分布之间有相当大的重叠。更重要的是，由于每日变化或测量误差，个体观察到的CV可能会有±3.1%的变化。在将个体分数与提议的截止点进行比较时，应考虑到CV分数的这个可能范围。由于个体的CV每日变化很大，且无法确定区分最大努力和次最大努力条件的精确截止值，因此必须谨慎解释CV分数，并且应该认识到过度依赖这种方法来识别不真诚努力时的潜在误差。
