Fine adaptive control of precision grip without maximum pinch strength changes after median nerve mobilization

Abstract

Fine dexterity critically depends on information conveyed by the median nerve. While the effects of its compression and vibration are well characterized, little is known about longitudinal tension and excursion. Using a force-sensitive manipulandum, a numeric dynamometer and Semmes Weinstein monofilaments, we examined the adaptations of precision grip control, maximum pinch strength and fingertips pressure sensation threshold before and immediately after the application of longitudinal tension and excursion mobilizations applied on the median nerve. Grip (GF ) and load (LF ) forces applied by the thumb, index and major fingers were collected in 40 healthy young participants during three different grip precision tasks along the direction of gravity. For grip-lift-drop task, maximum GF and LF and their first time derivatives were computed. For up-down oscillations, means of GF and LF and their variability were computed. For oscillations with up and down collisions, peaks of GF and LF , time delay between GF peak and contact, and values of GF and LF at contact were collected. Our findings show that median nerve mobilizations induce significant fine adaptations of precision grip control in the three different tasks but mainly during grip-lift drop and oscillations with collisions. Fingertips pressure sensation thresholds at index and thumb were significantly reduced after the mobilizations. No significant changes were observed for maximum pinch strength. We conclude that precision grip adaptations observed after median mobilizations could be partly explained by changes in cutaneous median-nerve mechanoreceptive afferents from the thumb and index fingertips.