“We were suspicious as we observed certain cases”, explained Ricard Pruna and Gil Rodas, doctors at F.C. Barcelona. “When we worked with football players who had suffered injuries to the long head of the biceps femoris, it seemed as though the players with shorter proximal free tendons, had a faster recovery. But as this was only our subjective impression, we decided to use the data available in order to study and thoroughly test our theory”.
The biceps femoris is one of the muscles that make up the hamstrings, which is one of the most injured muscle groups in sports such as football. Dr Xavier Yanguas, who is also a doctor at the club, has established that this type of injury accounts for 12% of all injuries suffered by football players, and 37% of muscle injuries. More specifically, 84% of hamstring injuries occur to the biceps femoris, hence its importance.
The biceps femoris muscle has two heads, one long and the other short. The first, which is more prominent, inserts into the ischial tuberosity of the pelvis through a tendon shared with the semitendinosus and can be studied as two separate sections: the intramuscular tendon and the free tendon, which is devoid of muscle fibre. The length of the free tendon is what appeared to influence recovery, which made certain biological sense: “Its length can influence the pennation angle formed by the muscle fibres and the muscle axis itself, which has been associated with the risk of injury and re-injury”, explained Rodas. The hypothesis had been formulated, but as with any scientific approach is needed to be verified, hence the study carried out by club doctors Ricard Pruna, Xavier Yanguas and Gil Rodas, together with leading international experts in muscle pathology including doctors Ramón Balius and Hans Tol. The results were recently published as a scientific letter in the Apunts. Medicina del Deporte journal.
A necessary but counter-intuitive study
The study included two large groups of athletes; one was made up of 50 F.C. Barcelona players, and the other used data taken from a sample of 58 players from the ASPETAR centre in Doha (Qatar) who had participated in a previous clinical trial.
All of the players had undergone an MRI to diagnose muscle injuries, which in turn allowed to measure the length of the free tendon; the distance between the ischial tuberosity and the point where muscle fibres begin to appear. This measurement was then compared with the progress (marked by the return-to-play – RTP) made by each athlete and its biceps femoris muscle injury. The length estimation was very reliable, with an almost perfect correlation when two radiologists interpreted the image independently or when it was re-analysed by the same specialist.
However, contrary to the prediction made, no statistically significant relationship was found between tendon length and the injury prognosis or RTP. In other words, having a longer free tendon does not necessarily mean a worse prognosis for biceps femoris muscle injuries.
Both measurements were within the normal parameters observed in other studies, but the variation between them is not associated. “The data is quite reliable as it includes a large number of players”, assured Rodas. One small flaw in the study could be that “the return to play criteria used by the doctors in the two groups were probably different”, he explained.
If this is the case, can the conclusions be seen as definitive? Maybe not. “Perhaps the study hypothesis could be proven with a larger sample”, said Rodas. “It is also possible that a subgroup of biceps femoral injuries, whether myotendinous or myofascial in different locations and with different characteristics, could be associated in some way. This is something that could be analysed in the future with a larger number of player”, he concluded.
The Barça Innovation Hub team