Two separate bipolar surface EMG electrode (circular 20 mm diameter, silver/silver chloride, Biopac Systems, Inc., Santa Barbara, CA) orientations (20 mm interelectrode distances) were placed over the flexor carpi ulnaris and extensor digitorum muscles of the affected and non-affected forearms. The parallel electrode orientation was placed in accordance with the recommendations from the SENIAM Project [25 ]. The skin at each electrode site was carefully abraded and cleaned with alcohol, and the impedance was less than 2000 Ω. The EMG signal from each electrode arrangement was amplified (gain: × 1000) using differential amplifiers (
EMG 100, Biopac Systems, Inc., Santa Barbara, CA, bandwidth 1.0–500 Hz).
The raw EMG signals were digitized at 1000 Hz and stored for subsequent analyses. All signal processing was performed using custom programs written with
LabVIEW programming software (Student Version 8.5.1, National Instruments, Austin TX). The EMG signals were bandpass filtered (fourth-order Butterworth) at 10–500 Hz, and the amplitude (microvolts root-mean-square, μVrms) was calculated for a 2.0 s time period corresponding to the middle 33% of the 6-s isometric muscle action.
Co-contraction was calculated by the coactivation index (CI) and was expressed as percent activation of antagonist over agonist [1 (
link)].
Zuniga J.M., Dimitrios K., Peck J.L., Srivastava R., Pierce J.E., Dudley D.R., Salazar D.A., Young K.J, & Knarr B.A. (2018). Coactivation index of children with congenital upper limb reduction deficiencies before and after using a wrist-driven 3D printed partial hand prosthesis. Journal of NeuroEngineering and Rehabilitation, 15, 48.