Saskia Baltrusch

91 Chapter 4 EMG monitoring Muscle activity was recorded using surface Electromyography (Cometa Srl, Milan, Italy, Bandwith: 100Hz, Input impedance: 20MOhm, Sampling Frequency: 2000Hz). Surface electrodes were placed at 7 bilateral sites on the skin after abrasion and cleaning with alcohol (Ag-AgCl electrodes†; interelectrode distance, 20 mm). The recording sites were: m. longissimus thoracis (LT) at the T9 level (4cm lateral), m. iliocostalis lumborum (IL) at the L2 level (6cm lateral), m. longissimus lumborum (LL) at the L3 level (3cm lateral), m. external oblique muscles (EO) about 15cm above the SIAS, m. rectus abdominis (RA), 3 cm lateral from the umbilicus, m. vastus medialis (VM) and m. biceps femoris (BF). Kinematic data To analyze movement patterns during lifting and walking we recorded 3D kinematics with an optoelectronic motion capture system (Optotrak, Northern Digital Inc., Waterloo ON, Canada) at a sample rate of 50 Hz. In the lifting trials, segment kinematics were measured using a dynamic three-dimensional linked segment model [24]. Cluster markers were attached to: lower and upper leg, pelvis, trunk, upper and lower arm, head, and box. Due to the fact that participants performed symmetric lifting, we only recorded kinematics from the right side of the body. To define the local segmental coordinate systems, anatomical landmarks were located through palpation and were related to the respective cluster markers using separate measurements (cf. [24]). In the walking trial only stride parameters were recorded using single heel markers attached to both shoes. 2.4 Testing procedure Before starting the experimental trials, resting metabolic rate was measured with the participant sitting in a chair for 5 minutes, followed by fitting and adjusting the two trunk exoskeletons to the participant. Subsequently, participants were instrumented with EMG equipment and maximum voluntary isometric contractions (MVCs) were performed against resistance to normalize EMG data collected during subsequent trials. 4