Abstract

Introduction: in rugby, some muscle characteristics visible with ultrasound have been related to the risk of injury to the long head of the biceps femoris. However, scientific evidence is scarce. Objective: to evaluate the changes in the morphofunctional ultrasound characteristics of the long head of the biceps femoris in rugby players of a professional rugby team at the end of the season. Material and method: a prospective analytical observational study was carried out at the University of Alcalá, with 19 players belonging to the Rugby Division Honor B team. Three ultrasound measurements were taken, measuring muscle thickness, perimeter, cross-sectional area and penile angle using the free software Fiji/Image, contraction and relaxation speed with M-mode, and the strength of the quadriceps and hamstring with a dynamometer. Results: significant differences were evidenced in quadriceps and hamstring strength and relaxation speed, with large and medium and significant effect sizes. When comparing backs and forwards, a significant effect was found on quadriceps strength of both the playing position factor and the training factor. In hamstring strength there was only a significant effect of the training factor. Conclusions: the results obtained in this study reveal, on the one hand, the existence of statistically significant differences in the variables of muscle strength of the quadriceps and hamstrings and relaxation speed, as well as in the muscle strength of the quadriceps when comparing backs and forwards; and on the other hand, there could be a relationship between the variables of pennation angle and muscle strength with the reduction in the risk of injury, which could provide a boost towards new research in this field. Regarding inter- and intraobserver reliability, it was moderate to excellent.