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Updated: Jul 15, 2026

Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations
Published on: May 1, 2018
Rugby Players Exhibit Stiffer Biceps Femoris, Lower Biceps Femoris Fascicle Length to Knee Extensors, and Knee
Gokhan Yagiz1, Nami Shida2, Hironobu Kuruma2
1Institute for Applied Human Physiology, School of Human and Behavioural Sciences, College of Human Sciences, Bangor University, Bangor,United Kingdom.
Purpose:
This study aimed to determine if hamstring-strain-injury risk factors related to muscle structure and morphology differed between rugby union players and controls.
Methods:
The biceps femoris long head (BFlh) fascicle length and passive muscle stiffness and relative and absolute muscle volume of knee flexors (KF) and extensors (KE) were measured in 21 male subelite rugby players and 21 male physically active nonathletes.
Results:
BFlh fascicle length was significantly longer (mean difference [MD] = 1.6 [1.7] cm) and BFlh passive muscle stiffness was significantly higher in rugby players (MD = 7.8 [14.8] kPa). The absolute BFlh (MD = 71.9 [73.3] cm3), KF (MD = 332.3 [337.2] cm3), and KE (MD = 956.3 [557.4] cm3) muscle volumes were also significantly higher in rugby players. There were no significant differences in the relative BFlh and KF muscle volumes. The relative KE muscle volumes were significantly higher in rugby players (MD = 2.3 [3.7] cm3/kg). However, the percentage BFlh fascicle length:KE (MD = -0.1% [0.1%]), BFlh/KE (MD = -0.9% [1.9%]), and KF:KE (MD = -4.9% [5.9%]) muscle volume ratios were significantly lower in the rugby players. BFlh muscle volume significantly correlated with BFlh fascicle length (r = .59, r2 = .35) and passive muscle stiffness (r = .46, r2 = .21).
Conclusion:
Future prospective studies should examine whether there are threshold values in BFlh passive muscle stiffness and BFlh fascicle length:KE, BFlh:KE, and KF:KE muscle volume ratios for predicting hamstring strain injuries.
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