Reliability and validity of indices of hand-grip strength and endurance

BACKGROUND/AIM: Grip strength is useful in clinical practice for the assessment of disease and/or rehabilitation progression. Brief maximal gripping is seldom required in everyday occupations, with repeated or sustained gripping at sub-maximal power more commonly involved. It has been proposed that assessment of both maximal hand-grip force and endurance is utilised. While the suitability of maximal contraction measures has been clearly established, the reliability and validity of other hand-grip indices have not been investigated. This study examined the reliability of various hand-grip indices and their validity in relation to distance walked during the six-minute walk test, a standardised exercise capacity test. METHODS: Subjects undertook static sub-maximal (50%) and maximal force contraction hand-grip testing from which various indices were derived, and six-minute walk testing from which distance walked was determined. Testing was repeated on three separate occasions for determination of test-retest reliability. RESULTS: Pre- and post-fatigue maximal contraction measurements demonstrated excellent test-retest reliability and validity. Conversely, other hand-grip indices were shown to be unreliable and exhibited no relationship with distance walked and hence concurrent validity could not be established. CONCLUSIONS: Based on the results of this study, it is recommended that pre- and post-fatigue maximal contraction may be utilised for the assessment of client ability and progression due to their established validity and test-retest reliability. However, previously proposed measures of fatigue such as endurance (duration of sustained contraction), Strength Decrement Index and work performed (function of endurance and force of contraction) are unreliable and invalid and may have limited use in clinical practice.