Figure 3.

Human reach and hold experiments, and analysis of kinematic and EMG data during posture and movement. (A) Experimental set up: the subject is seated at the table to make fast reaching movement of elbow joint in the horizontal plane. Subjects' arm and hand were secured on a manipulandum to keep the upper arm stable and ensure smooth extension and flexion of the forearm. Elbow angle (θ_el) is defined as the included angle between forearm and the extending line of upper arm. Movements with a range of 30, 45, and 90 degrees are performed in Block 1, 2, and 3, respectively. During extension, the elbow angle (θ_el) changes from initial posture of 90° to terminal posture of 0°, the filled dot indicates the holding posture between reaching movements. The reversal flexion from 0° to 90° has the same movement range and holding postures. The shoulder angle (θ_sh) kept at 90° during all experiments. (B) Analysis of kinematic and EMG data during posture and movement. During movement, the elbow moves from initial posture to terminal posture, and the movement onset (t₀) and offset (t₁) are defined as the time at which the velocity change (increases or decreases) is 10% of the peak velocity (V_peak). Initial posture period starts at time (t₀ – 1.5) and terminal posture is defined from time (t₀ + 4) after the angle stabilizes. The time window is 1 s. The tri-phasic EMG pattern of extensor Triceps long head (Tlh) and flexor Biceps short head (Bsh with inverse value) is shown in the bottom (low passed at a cut off frequency of 50 Hz with digital Butterworth filter).