Abstract
Hamstring strain injuries are common in sports, with the biceps femoris long head (BFlh)
muscle being the most frequently injured. BFlh injuries may result in changes to muscle
architectural parameters, including muscle thickness (MT), pennation angle (PA), and fascicle
length (FL). Ultrasound (US) is a non-invasive imaging tool capable of visualising muscle
architecture and providing real-time injury assessment. A limitation of standard static image
(SI) US is its narrow field of view, prompting the development of SI extrapolation equations,
extended field of view (EFOV), and wide field of view (WFOV) US techniques. However,
research of these techniques in relation to BFlh is limited. The aim of this study was to assess
the validity and reliability of these US techniques in cadaveric specimens and healthy
participants.
Lower limbs from eight cadavers (5 male, 3 female; mean age 80.3 years) were used to
assess BFlh architecture, employing each US technique to measure MT, PA, and FL. The
validity of the US measurements was evaluated by comparing them to the corresponding
physical measurements obtained following dissection. Additionally, measurements acquired
by each technique were compared in 20 healthy participants (10 male, 9 female, 1 non-binary;
mean age 19.2 years). Intra-rater reliability was assessed through repeated image analysis
(cadaver specimens and healthy participants) and repeated US scans (healthy participants).
Means and standard deviations of architectural parameters were calculated, and intra-class
correlation coefficients (ICCs) and Student’s paired t-tests were calculated to evaluate validity
and reliability.
At the femur midpoint, both SI and EFOV US techniques produced valid measurements
of muscle architecture when compared to dissection (ICCs: 0.84-0.98), except for PA measured
by EFOV (ICC: 0.73). EFOV demonstrated greater validity in measurements of FL than SI
throughout the muscle length. However, EFOV underestimated PA in comparison to
dissection. Comparison of US techniques in healthy participants found high agreement across
all architectural parameters (ICCs: 0.80-0.98). Both US techniques demonstrated acceptable
Iintra-rater reliability (ICCs: 0.75-0.99), except for FL in repeated EFOV scans (ICC: 0.61).
The investigation of WFOV US was withdrawn due to unforeseen circumstances.
The findings of this study demonstrate the strengths and weaknesses of US techniques in
assessing BFlh architecture. Both SI and EFOV are valid and reliable at the femur midpoint.
However, EFOV shows more promise in validity of FL measurement throughout the length of
BFlh. Future studies should investigate the potential positive implications of artificial
intelligence on both techniques and investigate the validity of WFOV.