All subjects were instructed to maintain a balanced posture during their
attempts on the balance platform. The balance of a human body is
limitedly stable due to the small fulcrum, as well as the high location
of the general center of mass of the body. Therefore, even the most
insignificant internal or external influences can disturb the balance
and result in the balance platform touching the floor.
During the experimental session, we were recording EMG
signals. The arrangement includes the following muscles: Tibialis
Anterior (TA), Gastrocnemius Medial head (GM), Rectus Femoris Straight
head (RF), Semitendinosus (ST). Before the electrodes were placed, the
subject was instructed on how to selectively activate each muscle to
optimize the EMG signal and minimize cross-talk from adjacent muscles
during isometric contractions. The signals were acquired via the
pre-gelled single-use electrodes Swaromed 1036 (Vermed, Austria) with a
silver/silver chloride sensor placed on the skin above the muscle. The
impedance was monitored after the electrodes were installed throughout
the experiments. Usually, the impedance values varied within a 2--5 kOhm
interval. The "Encephalan-EEG-19/26" (Medicom MTD company, Taganrog,
Russian Federation) with a set of A-5364 cables for EMG derivations was
used in the experiment. This device possessed the registration
certificate of the Federal Service for Supervision in Health Care No.
FCP 2007/00124 of 07.11.2014 and the European Certificate CE 538571 of
the British Standards Institute. We filtered raw EMG signals with a
band-pass filter with cut-off frequencies at 1 Hz (LP) and 100 Hz (HP)
and with a 50 Hz notch filter embedded in the hardware-software data
acquisition complex.
