STUDY DESIGN: Descriptive reliability study.

INTRODUCTION: A well-functioning wrist requires sufficient range of motion accompanied by adequate strength in every movement and direction-factors that are not regularly measured simultaneously in patients with wrist problems today. The ISOmetric Power device (ISOP) is a new instrument that measures isometric wrist force in all six directions of motion, but its intrarater reliability in a healthy population has not yet been evaluated.

PURPOSE OF THE STUDY: The purpose of this study was to perform an intrarater reliability test of the ISOP in healthy participants.

METHODS: Thirty-two healthy study participants (16 women/16 men; mean age 38.3 years; SD 6.5) were included. With a standardized testing protocol, the three planes of wrist motion- wrist flexion/extension, radial/ulnar deviation, pro/supination-were measured at one time interval (T1) and repeated after one week (T2). The results were analyzed using the intraclass correlation coefficient (ICC). A paired-samples t-test was also performed to determine if a statistically significant difference (P < .05) existed between the first and the second test values. Measurements with Jamar Dynamometer were performed at both time intervals, for internal control of measurement intrarater reliability.

RESULTS: Excellent correlations (ICC: 0.90-0.99) were found for all test-retests performed. The lowest value (ICC: 0.90) was seen for supination and the highest value (ICC: 0.99) for flexion of the left hand. No statistically significant differences were found in any of the pairs (P > .05) in terms of test-re-test, which additionally strengthen the correlation between the first and second test values.

DISCUSSION: Contrary to the Jamar Dynamometer, the ISOP is not designed for measuring grip strength, but for assessing the isometric muscle force in flexion, extension, pronation, supination, and radial and ulnar deviation. A systematic review has reported a moderate to strong correlation between isometric strength and dynamic performances. Thus, the ISOP is a more complete and applicable instrument for evaluating the functional strength in different directions in the upper extremity.

CONCLUSIONS: The ISOmetric Power device shows excellent intrarater reliability and is proposed to be a possible valuable wrist strength assessment tool to aid in both diagnostics and outcome measures of wrist and upper extremity disorders.