**2.2. Measurement of surface electromyography**

The SEMG signals are measured by three electrodes stuck on the forearm of the operator as shown in Fig.3. The electrode 1 was stuck on the musculus flexor carpi radialis, the electrode 2 was stuck on the musculus extensor carpi ulnaris, the electrode 3 was stuck on the musculus extensor carpi radialis longus, and the earth electrode was stuck on the wrist.

**Figure 3.** Allocation of surface electrode
