Vitrode f 150s

For GVS, electrical stimulation with a single rectangular pulse for 1 s was delivered from another constant-current isolator unit (SS-104J; Nihon Kohden Corporation). A pair of disposable surface electrodes (Vitrode F-150S, Nihon Kohden Corporation) was placed over the bilateral mastoid processes for bipolar stimulation [15 (link), 16 (link), 26 (link), 27 (link)]. We used two electrode montages for GVS: anodal and cathodal GVS (e.g., anodal GVS indicated that the right electrode was the anode). All of the subjects confirmed verbally that they perceived the roll of their head toward the anodal side during GVS [28 (link), 29 (link)]. The stimulus intensity of the GVS was expressed as multiplies of the threshold of the roll perception (i.e., perceptual threshold: PT). The PT ranged from 0.7 to 1.0 mA.

EMG recordings were made using bipolar Ag/AgCl surface electrodes (Vitrode F-150S; Nihon Kohden, Tokyo, Japan) on the TA, SOL, medial gastrocnemius (MG), vastus medialis (VM), and biceps femoris long head (BF) muscles. After cleaning the skin with alcohol, the electrodes were placed over the muscle belly with an interelectrode distance of 20 mm. The EMG signals were amplified (×1000) and filtered with a band-pass filter between 15 Hz and 3 kHz using a bio-amplifier system (MEG-6108; Nihon Kohden, Tokyo, Japan).

Surface electromyographic (EMG) signals were recorded from the SOL, medial gastrocnemius (MG), lateral gastrocnemius (LG), and tibialis anterior (TA) in the left lower leg. Ag-AgCl electrodes (Vitrode F-150S, Nihon Kohden, Tokyo, Japan) with an inter-electrode distance of 20 mm were used for EMG acquisition from each muscle (Saito et al., 2019 (link)). The amplifier was set to a gain of 1,000-fold with a band-pass filter between 5 Hz and 1 kHz (AB-611J, Nihon Kohden). The EMG signals and torque signals were simultaneously sampled at 4 kHz using an AD converter (PowerLab, ADInstruments, Melbourne, Australia) and stored on a personal computer using software (LabChart 7, ADInstruments). The root-mean-square (RMS) values of EMG signals of the SOL, MG, LG, and TA during the passive ankle dorsiflexion test were determined for the initial 5° and for the final 5° of dorsiflexion, respectively (Mizuno, 2023 (link)). In each intervention, the RMS values of EMG signals in the lower leg muscles ranged from 21.6 to 41.6 μV for the initial 5° and 21.5 to 40.3 μV for the final 5° of dorsiflexion. Thus, it was ensured that subjects relaxed their lower legs during the passive ankle dorsiflexion test by surface EMG recordings.

Electromyographic (EMG) activity was recorded unilaterally from the right (dominant in all the subjects) hand: (1) biceps brachii (BB), (2) triceps brachii (TB), (3) flexor carpi radialis (FCR), (4) extensor carpi radialis (ECR), (5) first dorsal interosseous (FDI), and (6) abductor pollicis brevis (APB) muscles. Surface EMG electrodes (Ag/AgCl; Vitrode F-150S; Nihon Kohden, Tokyo, Japan) were placed on the muscle belly of the right upper limb with an approximate interelectrode distance of 20 mm, whereas APB electrodes were placed over the muscle belly and first metacarpophalangeal joint, and FDI electrodes were placed over the muscle belly and the second metacarpophalangeal joint [23 (link)]. A reference electrode was placed around the lateral epicondyle. Prior to application of electrodes, skin was cleaned using alcohol swabs to reduce skin impedance. Signals were band-pass filtered (5–1000 Hz) and amplified (×1000) using a multi-channel EMG amplifier (MEG-6108, Nihon Kohden, Tokyo, Japan). All data were digitized at a sampling frequency of 4000 Hz using an analog-to-digital converter (PowerLab/16SP, AD Instruments, Castle Hill, Australia) and stored on a computer for post processing.

Electrical stimulation with a single rectangular pulse for 200 μs was delivered to the right ulnar nerve at the wrist with a pulse regulating system (SEN-8203; Nihon Kohden Corporation) and isolator (SS-104J; Nihon Kohden Corporation). A pair of surface electrodes (Vitrode F-150S, Nihon Kohden Corporation) was carefully placed on the optimal site for evoking a larger direct motor (M-) wave in the FDI at the lowest stimulus intensity. The stimulus intensity of the ulnar nerve stimulation was expressed as multiplies of the motor threshold (MT) of the FDI. The MT was defined as the minimum stimulus intensity that evoked an M-wave and twitch, which was confirmed by tendon palpation.

Surface electromyography (EMG) was performed on the right SOL muscle using surface Ag/AgCl electrodes (Vitrode F-150-S, Nihon Kohden, Japan). EMG signals were pre-amplified 1000-fold and filtered with a bandpass filter of 5–1000 Hz (MEG-6108, Nihon Kohden, Japan). All EMG signals were digitized at 4000 Hz using an analog-to-digital converter (Power lab/16SP, AD Instruments, Australia) and stored on a computer for offline analysis.

EMG activities were recorded unilaterally from right side of: (1) ES muscle on the 12th thoracic vertebral level (ES; trunk extensor muscle); (2) RA muscle lateral to the umbilicus (RA; trunk flexor muscle); and (3) tibialis anterior muscle lateral to the tibia (TA; lower-limb muscle). Two bipolar Ag/AgCl surface electrodes (Vitrode F-150S, Nihon Kohden) were placed over the muscle belly with 1 cm separation. A ground electrode was placed over the right anterior superior iliac spine. Before application of electrodes, skin was cleaned using alcohol to reduce impedance. All EMG signals were bandpass filtered (5–1000 Hz) and amplified (1000×) using a multichannel amplifier (MEG-6108, Nihon Kohden). All data were digitized at a sampling frequency of 4000 Hz using an analog-to-digital (A/D) converter (Powerlab/16SP, AD Instruments) and stored on the computer for postprocessing.