EMG and postural stability: parallel vs. semi-tandem foot position 4-Stage Balance Test

There is a lack of research that methodically clarifies baseline muscle tone values and demonstrates their activation during balance tests using selected parts of the 4-Stage Balance Test. The study involved 41 men and 34 women (mean age approximately 22 years (X = 21.83 y, SD 1.5 y)). Data were collected using a questionnaire containing socio-demographic and anthropometric data. Range of motion was measured using a goniometer (SFTR Goniometer Baseline 360 degrees), limb length and circumference were measured using a ADE MZ10021 tape measure and static balance was assessed using two tests from the 4-Stage Balance Test. Eight muscles (Rectus Femoris (RF), Vastus Lateralis (VL), Vastus Medialis (VM), Semitendinosus (S), Biceps Femoris (BF), Tibialis Anterior (TA), Gastrocnemius Medialis (GM), Gastrocnemius Lateralis (GL)) bioelectrical activity data were obtained using a Noraxon MR 400 sEMG device and MyoTrace software. Statistical analysis was performed using SPSS Statistics v25. In parallel foot position the highest EMG activity was observed in the VM (99.18 mV), S (55.27 mV) and RF (33.06 mV) muscles. In semi-tandem foot position the highest activity was observed in S (120.8 mV), GM (59.03 mV), and TA (47.84 mV) muscles, with the lowest in BF (6.58 mV) muscle. 1. Lowered base of support increases the activity of the semitendinosus and medial gastrocnemius muscles. 2. Maintaining the feet-together stance depends on the synergy between the semitendinosus and medial gastrocnemius muscles. 3. Maintaining semi-tandem positioned halfway in front of the other foot depends on the synergy between the vastus lateralis and tibialis anterior muscles.