Detecting submaximal efforts in grip strength testing with the coefficient of variation

The use of the coefficient of variation (CV) to determine level of effort in grip strength testing was examined empirically. Twenty-nine asymptomatic subjects participated in two conditions of testing: 100% effort and 50% effort. Order of conditions was counterbalanced and each subject was run in both conditions twice in the same order in order to assess the stability of the method. The number of trials (grasps) per condition was three for a total of 12 grasps for the study. The submaximal (50%) effort condition showed significantly more variability than the maximal effort condition in both sets of conditions (p<.01). Intra-class correlation coefficients were very low for both maximal effort and submaximal efforts (.036 and .025) indicating very low stability for the coefficient of variation. Classification rates were also found to have unacceptably large errors with 69% of the submaximal efforts being classified as maximal with the traditional 15% CV cutoff and 55% misclassification of submaximal efforts with an optimized 11% CV cutoff. It was concluded that the currently practiced method of using a low number of repetitions to calculate the CV may result in very unstable measures. Furthermore the "false negative" rate in using this method is unacceptably high for practical application. The implications of using the method and suggestions for improvement are discussed.