Background: No previous studies have investigated the test-retest reliability of tip, key, and palmar pinch force sense in healthy adults. The present study explores the test-retest reliability of tip, key, and palmar pinch force sense for different force levels in healthy adults during an ipsilateral force reproduction task. Methods: Fifty-six healthy subjects were instructed to produce varying levels of reference forces (10, 30, and 50% maximal voluntary isometric contraction (MVIC)) using three types of pinches (tip pinch, palmar pinch, and key pinch) and to reproduce these forces using the same hand. The subjects were tested twice by the same experienced testers, 1 week apart. Results: Based on the high values of the intraclass correlation coefficient (ICC), the tip pinch (0.783-0.895) and palmar pinch (0.752-0.903) force sense tests demonstrated good reliability for all the variables. The ICCs for the key pinch (0.712-0.881) indicated fair to good relative test-retest reliability. Conclusion: 1) This study demonstrates that high test-retest reliability of tip, key, and palmar pinch force sense in healthy adults can be achieved using standardized positioning and the proposed approach. 2) According to the reliability measurements, 30 and 50% maximal voluntary isometric contraction (MVIC) are the most reliable pinch force sense levels.

The aim of the current work was to verify three-dimensional directional effects on the reproduction error precision of the human upper limb position. Thirty male subjects without history of upper limb pathology were recruited from Renmin University of China. A three-dimensional position reproduction task in six directions (up, down, left, right, far, and near) was performed by each subject. The results suggested that the proprioceptive sense of upper limb position depends on the direction, with smaller absolute errors in Directions 4 (right) and 5 (far) than in Directions 1 (up), 2 (down), 3 (left), and 6 (near). Proprioception near the end of the elbow joint range of motion may be more reliable and sensitive. Subjects reproduced fewer ranges in the horizontal plane (Directions 3, 5, and 6) and they overshot the target position along the z-axis (vertical direction) except for Direction 6. Overestimations of position in the z-axis may be caused by overestimations of force.