Trigno wireless biofeedback system

Surface EMG (sEMG) activity was recorded using Trigno® Wireless Biofeedback System (Delsys Inc., Natick, MA). The sensors used are composed of two pairs of silver bar contacts with 10 mm interelectrode spacing; they have a sampling rate of 1926 Hz, a common-mode rejection ratio of 80 dB, and a 2.4-GHz transmission frequency. Before electrode placement, the skin was shaved and wiped clean with 70° alcohol to reduce impedance. Four electrodes were placed and secured with double side tape and kinesiology taping following the SENIAM recommendation and the anatomical location previously described (32 (link)).

PL EMG-BF training was performed with the Trigno® Wireless Biofeedback System (Delsys Inc, USA) and the “PL EMG”, which allowed the acquisition of signals in real-time. Subjects were seated in a highchair and held their legs in the air to allow an eversion movement. A screen in front of the subjects displayed the EMG signal. During the exercise, subjects were asked to use their PL EMG signal to trace a parabola curve displayed on the screen. This simulated daily muscle activation with gradual contraction and relaxation [42 (link)]. The peak of the parabola was set at 65% of the maximal electrical activity measured before training, which is similar to the PL activity during walking [12 (link)], making the training demanding but not too strenuous. The neuromuscular training lasted five minutes, divided into rounds of eight seconds of muscle contraction and fifteen seconds of rest. Before the training began, the task was demonstrated, and the investigator made sure that the subjects understood the task. The PL EMG-BF is shown in Additional file 1: Appendix III.

The handgrip and EMG evaluations will be synchronized using Labview v19 software (National Instruments Corp., Austin TX, USA) that makes it possible to simultaneously display feedback on strength and EMG activity. The handgrip dynamometer used will be the K-Force GRIP (K-Invent Inc., Montpellier, France), with 1000 Hz acquisition frequency and an accuracy of 100 g. The EMG signal will be recorded using the Trigno Wireless Biofeedback System (DelSys Inc., Boston MA, USA) with the Trigno Avanti™ electrodes, which are composed of a 4 silver bar contacts, 10 mm interelectrode, a 1926 Hz acquisition frequency per channel and with a second-order band-pass Butterworth filter set at 20–450 Hz and a second-order low-pass filter set at 100 Hz.