Effect of prone trunk-extension on lumbar and lower limb muscle stiffness

The role of muscle function and pointe shoe characteristics in Arabesque movement among ballet dancers with non-specific low back pain

This study aimed to investigate posterior chain muscle function and the influence of pointe shoes in ballet dancers with and without low back pain (LBP) in the Arabesque. Twenty-nine young professional ballet dancers (17 with LBP and 12 healthy controls) were recruited. Muscle strength and mechanical properties of the erector spinae and hamstrings were assessed. The displacement of centre of mass (COM) during Arabesque under different shoe conditions (R-class, Chacott, and own shoes) was measured with a motion capture system. The LBP group exhibited greater dynamic stiffness and decreased mechanical stress relaxation time in the lateral hamstring compared to the control group. During Arabesque, the LBP group demonstrated significantly greater anterior-posterior displacement of the COM and a larger percentage of time to achieve maximal trunk extension angle. The COM displacement in vertical and medial-lateral directions was smaller in the R-class than in their own shoes. LBP impacts muscle mechanical properties, particularly in the lateral hamstring. The compromised muscle function resulted in a longer time to spinal extension during Arabesque, signifying that reduced trunk control contributed to greater COM displacement. Hence, it is essential to emphasise that evaluating muscle properties and dynamic postural control is imperative for dancers experiencing LBP.

Effect of different isometric trunk extension intensities on the muscle stiffness of the lumbar and lower limbs

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.