Isometric strength assessment, Part II: Static testing does not accurately classify validity of effort

The purpose of this study was to determine if these two commonly-administered isometric tests are accurate indices of effort.

34 healthy subjects were tested once giving a maximum voluntary effort and once attempting to feign weakness of 50% of maximum.

During feigned weakness sessions, 20 of 34 subjects (58.5%), produced CVs of 15% or less during the Leg Lift. At the 95% CI, the expected frequency of false negatives for feigned weakness is 42.3 to 75.3% for the Leg Lift. At the 95% CI, the expected frequency of false negatives for feigned weakness is 51.9% to 83.3% for the Arm Lift.

Neither isometric lift is appropriate for classifying validity of effort. Use of these isometric lifts should be discontinued for the assessment of effort.