Lauren E. Pacinelli1, Ty B. Palmer2, John P. Vardiman1, Ryan M. Thiele1

1Kansas State University, Manhattan, KS; 2Texas Tech University, Lubbock, TX

PURPOSE: To examine the relationship between static ultrasonographic (US) measurements of biceps femoris (BF) pennation angle (PA) and passive musculotendinous stiffness (MTS) of the hamstrings measured during a straight-leg raise (SLR) assessment. METHODS: Twelve healthy college-aged females (mean±SD: age=22±2 years, mass=65±9 kg, height=165±5cm) volunteered for this investigation. For all US assessments, participants laid in a prone position, on a cushioned table, with their hip and knee resting comfortably in extension. US settings were enhanced to improve image quality, including the gain (50dB), depth (8cm), and frequency (12MHz). Images were captured with the US probe aligned with the long axis of the BF at 50% of the distance between the greater trochanter and the lateral joint line of the knee. PA measurements were analyzed using a third-party image analysis software and were identified as the angle formed between the muscle fascicles and the deep fascia of the BF muscle. Mean PA from two separate measurements was obtained from the highest quality image and used for subsequent analysis. Passive MTS of the hamstrings was quantified during a manually-applied SLR, which consisted of the investigator applying slow passive resistance against a load cell positioned immediately posterior to the heel, while the limb was moved toward the head. Stretches were performed on the right leg to the point of discomfort but not pain, as indicated by the participant. An electrogoniometer was used to measure the hip joint angle and MTS was calculated as the tangential slope of the passive angle-torque curve (Nm·deg-1) at the last common joint angle for all SLR assessments. Pearson product-moment correlation coefficients (r) were used to examine the relationships between passive MTS and PA. RESULTS: A significant negative relationship (r = - 0.647; R2 = 0.419; p = 0.023) was observed between PA (15.22° ± 2.47°) and MTS (0.75 ± 0.26 Nm·deg-1). CONCLUSION: The present study showed that BF PA is negatively correlated to passive stiffness of the hamstrings. This finding may be influenced by the variation in the fascicle alignment throughout the BF and the passive SLR being a global stiffness assessment of all three major hamstring muscles.

ACKNOWLEDGEMENTS: This study was supported and funded by the Mid-America Athletic Training Association.

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