Fig. 2

Placement of the surface electrodes. The electrodes were placed on the LD (1 cm lateral and inferior of the inferior scapular angle), ES (at level L1), MF (at level L5 on the line drawn from the posterior inferior iliac spine to the intervertebral space between level L1-L2) and GM (at the middle point between the posterior inferior iliac spine and the ischial tuberosity), with the patient in prone lying position. Placements of electrodes were decided based on the SENIAM recommendations (www.seniam.org) and expert opinions. Before admission of the surface electrodes (Ambu A/S, Denmark), skin preparation occurred by shaving, scrubbing and cleansing with alcohol. After electrode placement, 8 amplifiers were attached to the skin in the proximity of the measuring site. These amplifiers captured and amplified the electric signal prior to forwarding it to the desk receiver