Abstract
Both intrinsic and extrinsic hand muscles contribute to finger flexion; however there are different ways in which individuals can flex their fingers. Due to different muscle insertions, it is possible to distinguish the mechanical effect of intrinsic muscles from extrinsic muscles. The aim of this observational study was to investigate the degree to which individuals in the population rely on either their intrinsic or extrinsic hand muscles. A high frequency camera was used to record the hands of 31 healthy participants, aged between 18 to 40, while they made a fist repeatedly. The hands were placed on a horizontal plane and the video was taken from the ulnar side, aligned horizontally with the hand. The maximum vertical distance between the fingertip and the distal palmer creases (XY) was recorded using WIN analyze 3D software. Three examiners independently analysed the videos and classified them into intrinsic dominant, extrinsic dominant or a mixed pattern. A t-test was performed on the XY values for the three different categories. The XY height difference between the intrinsic and extrinsic groups were statistically significant (P=0.001). The XY of mixed and intrinsic was also statistically significant (p=0.012) but not for mixed and extrinsic (p=0.46). Assessment of time when movement starts at each individual joint showed significant difference with intrinsic predominant moving the MCPJ before IPJ and extrinsic dominant individual moving their IPJ before MCPJ. This study shows that there is a difference in hand muscle dominance between individuals. More importantly it shows that there are individuals who rely on their intrinsic hand muscles more than their extrinsic muscles.
