Kinematics of the fingers during typing
When typing on a keyboard, the fingers may be in awkward postures, making repetitive motions, and exerting high forces which are risk factors of cumulative trauma disorders. In this experiment, the kinematics of the fingers while typing were investigated for 12 right-handed subjects (6 male and 6 female) to gain a better understanding of factors which influence how a finger strikes a key. The apparatus for this experiment included an exoskeleton to determine angular displacements of the finger joints and a motion analysis system to determine the coordinates of the wrist and the keys on the keyboard.
This experiment examined four dependent variables: the fingertip angle with respect to the horizontal at the point of contact and at the point of maximum depression of the key, and the linear vertical and horizontal components of velocity of fingertip due to the finger joints at the point of contact with the key. The factors investigated included Gender, Finger (Index, Middle, and Ring), Row (Upper, Middle, and Lower), and Digraph (typing two letters with the same finger, with two fingers on the same hand, or with two opposite hands).
The results indicated that for all four dependent measures, there was a significant difference between all three levels of Row. For the factor Finger, there was no significant difference between the middle and ring fingers. Typing with the index finger, typing two letters with the same finger, or typing on the upper row resulted in smaller fingertip angles than the other conditions. All levels of Digraph resulted in significantly different linear vertical velocities of the fingertip while certain combinations of the levels of Finger, Row, and Gender were significantly different for the linear horizontal velocities.
From the results, it appears that the methods employed in this experiment were effective to measure the angle of the fmgertip at the point of contact and at the point of maximum depression and to measure the linear vertical and horizontal components of velocity produced by the finger joints. The results for the linear vertical and horizontal components of velocity for the fingertip also indicate that the wrist velocity (which was not measured) may contribute to the overall fmgertip velocities at the point of contact with the key and for this reason, should be examined in future research.