Trigno wireless system

Prior to exercise, the right upper-limb was prepared for EMG. The skin over the biceps brachii, brachioradialis, and anterior deltoid was shaved, abraded, and cleansed with alcohol. Wireless surface electrodes were placed on the skin (Trigno Wireless System, Delsys, Natick, USA; sampling rate: 2148 Hz; bandwidth frequency: 20–450 Hz). The biceps brachii electrode was placed along the longitudinal midline and over the distal-most portion of the muscle when the elbow angle was 90°. For brachioradialis and anterior deltoid, electrodes were placed over the most distal portion of the muscle bellies as determined by palpation. All electrodes were secured to the skin with tape. The EMG signals were acquired with electrode manufacturer’s software (Delsys EMGworks Analysis 4.7.9).
An electrogoniometer was used to measure elbow joint angle during exercise (Biometrics Ltd, Ladysmith, USA; sampling rate: 519 Hz; gain: 1400 dB). The goniometer consisted of two endblocks connected by a wire that had strain gauges mounted around it, with the wire protected by an outer spring. Using double-sided tape, the proximal and distal endblocks were secured to the medial sides of the humerus and forearm, respectively. The mid-point of the spring was positioned at the medial epicondyle of the humerus.

Bilateral surface EMG was performed for six spinal and abdominal muscle groups: rectus abdominis (RA) (3 cm lateral to umbilicus)^{36 (link)}, oblique externus (OE) (15 cm lateral to umbilicus)^{37 (link)}, erector spinae at L3 (ESL3) (3 cm lateral to the L3 spinous process)^{36 (link)}, erector spinae at Th9 (EST9) (5 cm lateral to the T9 spinous process)^{38 (link)}, erector spinae at Th1 (EST1) (5 cm lateral to the T1 spinous process)^{38 (link)}, and latissimus dorsi (LD) (lateral to T9 over the muscle belly)^{37 (link)}. The activities of the muscles were recorded using a wireless EMG system (Trigno Wireless System, DELSYS, Boston, MA, USA). Each electrode had an inter-electrode spacing of 10 mm. The EMG signals were bandpass filtered (20–450 Hz), amplified (with a 300-gain preamplifier), and sampled at 1000 Hz. To prepare the skin for electrode placement, natural oil and other contaminants were removed from the skin surface with an alcohol swab. The starting point was initiated with the verbal cue “go” when the examiner manually pressed the electrical trigger once^{10 (link),39 (link)}. After participants completed the tasks and returned to a resting posture for approximately 1 s, the examiner manually pressed the electrical trigger twice with the verbal cue “end” to define the end of the movement^{10 (link),39 (link)}.

Wireless EMG sensors (Trigno EMG sensors, DELSYS, Boston, MA, United States) were placed on the bilateral medial gastrocnemius (MG) and SL muscles according to the SENIAM recommendations¹, after the skin was gently abrased and cleaned with alcohol, as these two muscles are mainly involved in postural control (Masani et al., 2003 (link); Heroux et al., 2014 (link)). The sensors were placed as far as anatomically possible from each other to minimize the potential risk of cross-talk between the EMG recordings (Hansen et al., 2005 (link)). EMG signals were amplified and filtered (band pass filter of 20–450 Hz) using a bio-amplifier (Trigno Wireless System, DELSYS, Boston, MA, United States), and sampled at 2000 Hz. Force signals were also recorded using a force plate (Tec Gihan, Kyoto, Japan) at a sampling rate of 1000 Hz to compute the COP position. A customized LabVIEW program (National Instruments, Austin, TX, United States) was used to display the horizontal lines and COP position on the PC monitor.

We used a special bike (Retül Müve SL Dynamic Fit Bike) and a dynamic bike fitting system (Retül bike fitting system, Boulder, CO, USA) to control the standard cycling position while allowing us to change the KFOF parameter only. The Delsys Trigno Wireless System (Delsys Inc., Natick, MA, USA) was used to record muscle activation in the lower limb. The surface electrodes had four silver bar contacts (5 × 1 mm) spaced 10 mm apart in a rectangular configuration. Before the riding tests, the electrodes were placed at the vastus lateralis (VL), vastus medialis (VM), semimembranosus (SEMI), biceps femoris (BF), gluteus maximus (GM), tensor fascia lata (TFL), medial gastrocnemius (MG), and tibialis anterior (TA) of the right leg according to the method described in the previous study [18 (link)]. A portable metabolic system (COSMED K4b2) and a chest strap of the heart rate monitor (POLAR) were used to collect data on oxygen consumption (VO₂) and heart rate during the cycling exercise testing.