**2.3. Common experimental set-up**

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 them gave their informed consent.

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 and extensor muscles.

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 times in each session.

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 a chair, with the forearm and the arm forming an angle of about 15o . The forearm of the righthand 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 them. The subject was then given a brief explanation of how the system functions.

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 maximum detected value). The EMG signals of each subject were normalized to the range of 0-1 by their respective MVC values.

To familiarize the subject with the equipment and functioning of the simulator, the subject was firstly instructed to freely move the virtual hand contracting his forearm muscles. When he felt comfortable with the system, the different sessions of experiments were performed. In order to avoid fatigue, a rest was scheduled between tasks, and the subject was not asked to keep any of the postures for more than a few seconds (Basmajian and Deluca, 1985; Kampas, 2001).

After the experiments, a short questionnaire was given to the amputee volunteer to gather feedback on the *Osaka Hand* and on its simulator. Some questions were based on the surveys described by Sears and Shaperman (1998) as well as Atkins *et al.* (1996). This gathered infor‐ mation allowed us to plan the direction of our future research.
