**3. Experiments and results**

*2.2.3. Display system*

subject to achieve the proposed goal.

276 Electrodiagnosis in New Frontiers of Clinical Research

**2.3. Common experimental set-up**

them gave their informed consent.

and extensor muscles.

times in each session.

The tasks depicted in Figure 3(c1) to (c4) were implemented in a program that used OpenGL graphical library to represent the virtual arm and prosthetic hand by the wire-frame drawing shown in Figure 3(d). The refresh rate was 25 frames/s, which was sufficient to give the impression of smooth motion. In addition, the GW displayed the processed EMG signals used as input. During the experiments, supplementary information was displayed to guide the

To test the performance, validity, and controllability of the simulated hand, several experi‐ ments were carried out with three male, able-bodied subjects aged 22, 24, and 32; and a 43 years-old male who had both hands amputated 18 years earlier after a traffic accident. All of

The amputee subject uses a body-powered hook at the end of the right upper limb and a bodypowered hand at the end of the left upper limb. He had worn a myoelectric prosthetic hand on the right upper-limb until four years before the experiment. Since then, he has not been actively using his forearms muscles; for this reason, he suffered from muscular atrophy (very weak muscles) in both forearms. Consequently, his EMG signals corresponding to the maximal voluntary contraction (MVC) had a value of less than 20% of the average MVC of the three non-amputee subjects (0.65V/3.51V). In addition, he exhibited a slightly higher level of involuntary co-contraction (simultaneous contraction of antagonist muscles) in his wrist flexor

All subjects performed the same protocol composed of four sessions. One session consisted of two different tasks: angle and position control. Subjects repeated these tasks from three to five

The subject sat barefoot in a chair, with one foot on a steel sheet on the floor in front of the chair and with sleeves rolled up to expose the forearm. The steel sheet was used as reference voltage for the EMG processing unit. The subject was instructed to sit in a relaxed position in

hand was cleaned with SkinPure skin abrasion gel (NIHON KOHDEN Corp., Tokyo, Japan) and ethanol. A pair of bipolar, surface electrodes (Ag-AgCl, 1 cm in diameter; NIHON KOHDEN Corp., Tokyo, Japan. Type NS-111U) was attached, with a centre-to-centre distance of about 2 cm, following the muscle fiber direction of the wrist flexor muscle (*flexor carpi radialis*), and another pair was positioned on the wrist extensor muscle (*extensor carpi radialis brevi*). Gelaid electrode paste (NIHON KOHDEN Corp., Tokyo, Japan) was placed in the contact area between the skin and the electrodes to ensure good electric conductivity between

Before starting the experiments, the subject was instructed to exert for 1 second his maximal contraction of each target muscle from which the EMG signals were taken. The simulator calculated the MVC amplitude value for each muscle as the average around its EMG peak (the

them. The subject was then given a brief explanation of how the system functions.

. The forearm of the right-

a chair, with the forearm and the arm forming an angle of about 15o

Two types of experiments were carried out; the ones of the first block (3.1) were oriented to check whether the behavior of the simulator corresponded to the behavior of the *Osaka Hand*. The experiments of the second block (3.2) checked the controllability of the simulator.
