Publications

Purpose: To investigate the effect of isometric prone trunk extension (IPTE) contraction intensity on the stiffness of erector spinae (ES), semitendinosus (ST), biceps femoris (BF), and gastrocnemius muscles to understand the overall muscle mechanical behavior during IPTE and to explore the mechanisms of oordinated contraction of the body kinetic chain.

Methods: Twenty healthy females were recruited, and participants underwent IPTE at three contraction intensities, i.e., 0% maximum voluntary isometric contraction (MVIC), 30% MVIC, and 60% MVIC, and muscle stiffness was measured using MyotonPRO.

Results: Muscle stiffness was moderately to strongly positively correlated with contraction intensity (r = 0.408–0.655, p < 0.001). The percentage increase in stiffness at low intensity was much greater in ES than in lower limb muscles and greater in ST and BF than in gastrocnemius, whereas at moderate intensity, the percentage increase in stiffness decreased in all muscles, and the percentage increase in stiffness in ES was lower than that in ST. There was a moderate to strong positive correlation between ES stiffness variation and ST (r = 0.758–0.902, p < 0.001), BF (r = 0.454–0.515, p < 0.05), MG (r = 0.643–0.652, p < 0.01), LG (r = 0.659–0.897, p < 0.01).

Conclusion: IPTE significantly affected the stiffness of lumbar and lower limb muscles, and low-intensity IPTE activated the ES more efficiently. There were significant coordinated muscle contractions between ES, ST, and LG. This provides preliminary evidence for exploring the overall modulation pattern of the lumbar and lower limb muscles’ kinetic chains. In future studies, we will combine other stiffness assessment methods (such as Magnetic Resonance Elastography, Shear Wave Elastography, or electromyography) to corroborate our findings.

Keywords: MyotonPRO, erector spinae, stiffness, isometric prone trunk extension, coordinated contraction

In this study, we found that ES and lower limb muscles exhibited different muscle mechanical behaviors at different contraction intensities of IPTE. Muscle stiffness showed a moderate to strong positive correlation with contraction intensity, with 30% MVIC being the optimal intensity for effective ES activation. ES and lower limb muscle have a moderate to strong correlation between the stiffness percentage change, and there were significant coordinated muscle contractions between ES, ST, and LG. In this study, we provided preliminary evidence that coordinated contraction of the lumbar and lower limb muscles occurs during isometric prone trunk extensions, which provides a further reference for us to understand the overall regulation mode of the muscle kinetic chain. In future studies, we will combine the use of other stiffness assessment methods (e.g., Magnetic Resonance Elastography, Shear Wave Elastography, or electromyography) to corroborate our findings.