Veraksits, A. | bioRxiv Science

bioRxiv2024

Dissociation between biomechanical stiffness and sEMG activity in trapezius and lumbar skeletal muscles in steady postures

BackgroundProlonged sitting posture and sedentary behaviour, spent mostly in sitting are harmful for general health. The low back and shoulder area are the most vulnerable. In these regions the sEMG registration of neuromuscular activity shows low activity in steady postures. Stiffness of according muscle can be measured by myotonometry. We were not able to find any direct comparison between these parameters although separately, direct correlations between contraction force and sEMG or stiffness have been clearly established. Research questionWhether and how stiffness is modulated by neuromuscular activity in standing, lying or in different sitting postures in these vulnerable regions. MethodsThe muscles biomechanical stiffness (measured with MyotonPRO) and mean power frequency (MPF) with amplitude (AMP) on surface electromyography (sEMG) were registered in the upper part of musculus trapezius (UT) and musculus erector spinae (ES, at the level of L4 vertebrae). Nine healthy physically active males aged 19-46 (mean{+/-}SD, 28.6{+/-}10.9 years), participated in the study. The standing, prone, and three sitting postures where studied. The latter were distinguished by the back-tight-angle (BTA): 1) sitting on a common chair, straight back, BTA 90{degrees}), 2) slumped sitting on the same chair (BTA<90{degrees}), and 3) sitting on an experimental chair with a convex base, BTA 115-120{degrees}. Results and SignificanceMuscle stiffness did not correlate with either of the sEMG parameters in ES but did so only in low grade with the AMP in UT (Spearman rank {rho}=0.24, p=0.02). It was interesting that contrary to UT, in ES a significant positive correlation ({rho}=0.24, p=0.02) was noted between MPF and AMP. It is likely that the steady body position under the Earths g-force may be ensured by the biomechanical characteristics of the tissue rather than neuromuscular activity. This can be explained by incompressible nature of soft tissues and be a less resource-consuming strategy. HighlightsO_LIMuscle stiffness in the low back is similar to standing straight and lying. C_LIO_LIIn steady postures muscle stiffness does not correlate with neuromuscular activity. C_LIO_LIBody position is consolidated by the muscles biomechanical stiffness. C_LI

biophysics↗

bioRxiv2023

Rectus Femoris Muscle Elasticity and Stiffness Correlates with Maximal Oxygen Consumption in Triathletes

VO2max is considered single best indicator of cardiovascular fitness and aerobic endurance. We analyzed retrospectively, are there any relationships between muscle parameters and oxygen consumption in a study where the myoton equipment was used to establish muscle biomechanical properties, such as elasticity, stiffness, and tension (measured as oscillation frequency) in triathletes. Eight muscles were studied in 14 male triathletes over three years. Relaxed and contracted states of muscles were measured. VO2max was recorded in these athletes up to four times during this period. Average values were calculated for each athlete and High (max 71.8-min 62.3 ml/kg/min) and Low (59.1-51.3) oxygen consumption groups were formed. Higher oxygen consumption correlated significantly (r=-0.58; p=0.029) with improved elasticity (represented by smaller decrement values) of the rectus femoris muscle in a contracted state. Also, in the High VO2max group, this muscle (in a relaxed state) was significantly more elastic and stiffer at the same time compared to the Low group. An ultrasound registration was also conducted to observe the depth of the devices impact in the posterior crural muscles. It was confirmed that deep and substantial tissue disturbances were caused by this impact. According to our findings, myotonometry is an adequate method to establish muscle parameters. Elasticity and stiffness of the rectus femoris muscle may determine success in triathlon.

physiology↗