Grip force monitoring on the hand: Manugraphy system versus Jamar dynamometer

For clinical grip force assessment, the Jamar dynamometer is a wide accepted tool. Users have to be aware that this method does not represent all grip efforts applied. The Manugraphy system is a tool that measure total grip force as well as identify load distribution patterns of the hand while gripping cylinders wrapped with calibrated capacitive matrix sensor mats. The aim of this study was to validate an assessment setting of the Manugraphy system for clinical use. Further, the relationship and difference between the Manugraphy system and the Jamar dynamometer were investigated. At two study centers, 152 healthy volunteers performed grip force tests with a digital Jamar dynamometer using handle positions 3 and 4 and the novel(A (R)) Manugraphy system using two cylinders with circumferences of 150 and 200 mm. The subjects performed grip force testing with both devices on three different days. The intra- and inter-day variability for both methods was evaluated. To compare the values of both systems, the Spearman correlation coefficient was calculated. The force values, as measured by the sensor matrix, were higher than those of the Jamar dynamometer. Analyses showed significant positive correlations between values obtained by the two measurement methods (p < 0.001). There was no significant inter-day variation for the 200-mm cylinder of the Manugraphy system. For the 150-mm cylinder, a significant variation was observed at center B, but not at A. Nevertheless, the fluctuation of the grip force values obtained with the Manugraphy system was equal or better than those obtained with the Jamar dynamometer. The force values, obtained using the two systems, have a high correlation but are not directly comparable. Both systems allow valid and constant grip force measurement. As the sensor mat detects all forces applied perpendicularly to the cylinder surface, it characterizes grip force better than the Jamar dynamometer. In addition, information about load distribution of the hand is gained.