Author(s): OLIVEIRA, L., BRANDÃO, M.C., PALMIERI, D., VICTORINO, Y., Institution: UNIVERSIDADE FEDERAL DO RIO DE JANEIRO, Country: BRAZIL, Abstract-ID: 2004

INTRODUCTION:
The lumbar multifidus muscle is fundamental for spinal stabilization and trunk movement, and changes in its mechanical properties, particularly stiffness, have been associated with low back pain [1,2]. Shear wave elastography by SuperSonic Imaging (SSI) offers a non-invasive method to assess in vivo muscle stiffness through the shear modulus (μ) [3]. Although static stretching is commonly prescribed to alleviate symptoms and improve mobility, no studies have investigated changes in muscle stiffness during stretching. Therefore, this study aimed to examine the behavior of the lumbar multifidus µ in both superficial and deep layers at the L4–L5 level before, during, and after a session of static stretching..
METHODS:
Twenty-two healthy men participated in the study. The study was approved by the Ethical Committee (nº 3.672.989), and all participants provided informed consent. Participants had not engaged in stretching practice for at least one year and had no history of low back pathology. The protocol included SSI elastography assessment of lumbar multifidus stiffness at rest, during, and after a single 3-minute static stretching intervention, where they sat on their heels, with maximum trunk flexion and arms extended forward. Functional test (Schober test) was performed before and after stretching.
RESULTS:
Functional test performance improved significantly after stretching. No significant differences in μ were observed between layers before the intervention. However, immediately after stretching, multifidus μ was significantly lower in the deep layer than in the superficial layer. Considering the change in μ from the first to the last minute of stretching for each layer, K-means clustering identified two response patterns during stretching: responders (reduction in µ) and non-responders (increase µ). For the superficial layer, half of the participants were classified as responders and the remaining half as non-responders, whereas in the deep layer, 75% were classified as responders.
CONCLUSION:
A single 3-minute session of static trunk flexion stretching improved functional mobility, which may be attributed to other muscles and connective tissues involved in the stretching maneuver. The multifidus deep layer exhibited lower stiffness than the superficial layer only after stretching, suggesting a region-specific effect of the intervention. During stretching, distinct response patterns were observed among participants, with most showing a tendency toward decreased stiffness in the deep layer. These findings support the use of SSI elastography to assess individual tissue behavior during the intervention and highlight the importance of considering interindividual variability in responses to stretching.
REFERENCES:
1. Masaki M et al. Clin Biomech, 2017.
2. Koppenhaver et al. Musculoskelet Sci Prat, 2020.
3. Gennisson et al. Diagn Interv Imaging, 2013.