Author(s): WINIARSKI, S.1, MOLEK-WINIARSKA, D.2, Institution: WROCLAW UNIVERSITY OF HEALTH AND SPORT SCIENCES, Country: POLAND, Abstract-ID: 2459

INTRODUCTION:
The purpose of the study was to assess the changes in muscle fatigue and stiffness of the muscles stabilizing the body in the sitting position in administrative workers of a corporation.
METHODS:
45 participants were divided into intervention (N=22) and comparison (N=23) groups and tested before and after PT training. The exclusion criteria were serious health problems or a certified degree of disability.
Muscle fatigue and stiffness were assessed for the muscles crucial for maintaining upright posture and spinal stability: upper and lower Trapezius Descendens (Trap.Up, Trap.Lw), Erector Spinae in the lumbar (ESpin.Lumb) and thoracic region (ESpin.Thor). Calculations of the EMG signal using Noraxon Ultium EMG included the use of an FIR filter, smoothing, reduction of artefacts, and calculation of the slope of the median frequency curve (in Hz/s) for each muscle on the right and left side.
Participants performed an endurance test in a sitting position with a 30° trunk forward inclination, holding 2kG weights in their hands. This forced position lasted until the moment of the participant’s refusal.
Muscle elastic stiffness (in N/m) of the damped oscillation was tested by the MyotonPro device.
The PT training covered physical exercises to reduce tension and fatigue of muscles used during a long-term sitting position.
RESULTS:
In summary, the intervention group showed a significant decrease in stiffness in the upper trapezius (from 417.6 to 344.0 N/m, p=0.02) and erector spinae (from 573.1 to 494.9, p=0.01) central on both sides. A slight insignificant decrease was also observed in the erector spinae inferior (from 284.7 to 243.6 N/m, p>0.05) on the left side, with a small increase on the right side (from 292.5 to 287.4 N/m, p>0.05).
The intervention group showed a general trend of reduced muscle fatigue rates across all measured muscles (on average from -0.075 to -0.022 Hz/s on the left and right side) post-intervention, as indicated by the less negative slope of the median frequency.
CONCLUSION:
The median frequency of the EMG signal reflects the frequency spectrums central point. It is influenced by both the muscle fiber conduction velocity and the recruitment of different types of muscle fibers. As muscle fatigue progresses, there is a noticeable shift in the median frequency towards lower values. The stiffness measurements revealed a general decrease in muscle stiffness in the intervention group post-treatment, suggesting the potential effectiveness of the intervention in alleviating muscle tension due to prolonged sitting.
Fatigue assessment through median frequency slope analysis indicated that the intervention group experienced a reduction in the rate of muscle fatigue, as evidenced by the less negative slope post-intervention.
These findings support the application of dedicated physical therapy interventions tailored for individuals who experience the effects of long sitting positions, which may include strategies to reduce stiffness and slow down the onset of fatigue.