Finger Forces and High-Density sEMG Analysis By Implementation of a Handheld Device

Human hand is capable of performing various accurate motions as it is controlled by several intrinsic and extrinsic muscles simultaneously. Due to the complexity of hand physiology, it is especially challenging to achieve an efficient hand exoskeleton control for patients with affected motor functions. A preliminary investigation demonstrated a technique to identify common synaptic input for various finger pinching motions. It is, therefore, possible to extend the findings towards an efficient control algorithm, even with patients with neurological diseases. Several devices have been developed in the past with the aim to measure and evaluate finger forces, but an adjustable and portable device providing individual digit force recordings in both direction (flexion and extension) is still missing. Hence, this work presents the development of a handheld and lightweight system, capable of measuring finger forces in different grasping dimensions, and the graphic user interface for its management. In comparison to previous works, this work presents for the first time individual finger extension force measurements on a portable device. Three subjects were recruited and an experiment was conducted to investigate the muscle activity of the hand together with finger forces, during common digits motions. The experimental protocol repeats motions that are commonly used in daily activities, including fingers flexion and extension movements, pinching and grasping with different finger combinations, during which High density electromyographic signals (HD-sEMG) were recorded from six different muscles: First Dorsal Interosseous, Dorsal Interossei, Abductor Digiti Minimi, Thenar, Extensor Digitorum, and Flexor Digitorum Superficialis. Two different activities were evaluated: steady contraction and sinusoidal force production. An NMF was therefore performed in order to identify common synergistic strategies operating during the aforementioned tasks. This preliminary examination showed the presence of hand muscle synergies and identified control signals, which can be possibly used in future motion control applications.