Fingers’ Biomechanical Analysis with Smartphone User Tests

With the increase in life expectancy, some new information and communication technologies become poorly adapted to elderly, especially with devices of small size as smartphones for example. In order to predict and improve the accessibility of people with limited forearm motor capacity the paper deals with the study of interaction modalities based on EMG (electromyography) for human-computer interaction, for a more tolerant interaction in the face of vagueness of the gesture. For this purpose series of tests for finger activity estimation were performed according to an appropriated bio-medical protocol (two cases: with and without a strap) while manipulating a smartphone. The EMG signals of the three most involved muscles of the thumb were recorded and analyzed. The results shown that the finger’s EMG signals for these muscles are interdependent. It was found that the relationships between positions of touch, for five orders dots disposed on the smart phone screen, and applied force were no linear. The quantitative relationships between force and fingers’ displacements have been extracted by using linear regression analysis. Based on the comparison of force-displacement relationships, it is observed that the thumb induces less activating force than the other fingers. It was also found that the relief of the finger muscles involved in the gripping of the smartphone allows to reduce the muscular activity of the thumb and thus to delay the appearance of musculoskeletal disorders.