Author(s): MIKATA, S., KAWAMA, R., OKUDA, Y., SATO, K., TAKAHASHI, K., WAKAHARA, T., Institution: DOSHISHA UNIVERSITY, Country: JAPAN, Abstract-ID: 1867

INTRODUCTION:
Changes in joint angle alter passive tension applied to the muscle-tendon unit and its surrounding connective tissues. When the muscle-tendon unit is elongated by changes in joint angle, both muscle and deep fascia stiffness increase [1, 2]. This angle-dependent increase in stiffness reflects changes in tissue loading and could be involved in force transmission within the musculoskeletal system. Although the stiffness of muscle and deep fascia has been reported to differ across regions within the quadriceps femoris [3, 4], it remains unclear how the stiffness of these regions varies with to changes in joint angle. Clarifying whether stiffness changes differ across anatomical regions may help to better understand how the quadriceps femoris distributes mechanical load during passive elongation. Here, we examined region-specific changes in deep fascia stiffness within the quadriceps femoris at different knee flexion angles.
METHODS:
Shear wave elastography was used to measure shear wave velocity (SWV) of muscle and deep fascia as an index of stiffness in 25 healthy males. The SWV was measured under passive conditions in the proximal and distal regions of the rectus femoris, vastus lateralis, and vastus medialis at knee flexion angles of 0 (full extension), 45, and 90 deg. In addition, we measured SWV in the medial and lateral regions of the vastus lateralis. Linear mixed-effects models were used to test the effects of region, knee flexion angle, and their interaction.
RESULTS:
Muscle SWV increased with knee flexion angle in all examined regions of the rectus femoris, vastus lateralis, and vastus medialis (all p < 0.001). A significant interaction between region and knee flexion angle was found for the SWV of deep fascia (p < 0.01). The deep fascia SWV increased with knee flexion angle in most regions (p < 0.001), whereas no significant change in deep fascia SWV was detected in the proximal-lateral region of the vastus lateralis across the tested angles (p = 0.998).
CONCLUSION:
Across the quadriceps femoris, the muscle stiffness increased consistently with knee flexion angle, whereas the deep fascia stiffness changed differently between regions. The mechanisms underlying these regional differences may be related to regional variations in fascial microstructure, such as differences in collagen fiber organization and multilayered structure [5]. Such region-dependent stiffness changes suggest complexity of local mechanical loading within the vastus lateralis, and may be relevant when considering region-specific effects of stretching.

REFERENCE:
[1] Chen B. et al., Sci Rep, 2020
[2] Chanel B. et al., Translational Sports Med, 2025.
[3] Kodesho T. et al., Eur J Appl Physiol, 2021.
[4] Otsuka S. et al., J Biomech, 2020
[5] Otsuka S. et al., J Biomech, 2018