31 Mar The FSI Conference 2021: Martino Franchi

The hamstrings are the most common location of injuries in football (37%), in which biceps femoris long head (BFlh) is the most injured muscle (86%). These injuries can cause structural disruption at the muscle and connective tissue level. Muscle architecture properties seems to be related to function and capacity of the muscle and potentially related to hamstring injuries.

Different muscle contractions can result in different architectural arrangements, with eccentric promoting increased length in fascicles due to more sarcomeres in-parallel. For example, the Nordic hamstring exercise (NHE) acts in the structural component of the muscle by increasing it. The addition of sarcomeres in series that could provide this kind of exercises has shown to be protective of the muscle in high-intensity football-specific activities such as sprint or change of direction. However, this changes in fascicles length are not easy to corroborate with ultrasounds in which a small portion of the muscle is displayed, potentially overestimating fascicle length and, hence, changes in architecture. At this respect, even though sarcomerogenesis has been observed in animals, the only study to date in humans showed that after eccentric training no sarcomerogenesis occured, which suggests that hamstrings injuries are not only a matter of contractile properties, but the connective tissue and neuromechanics play a critical role in the process.

Therefore, although literature showing eccentric exercise may increase fascicle length is useful to better know how muscles can be stimulated, with simple images of muscle architecture it cannot be told the whole history of hamstrings injury prevention.

Question: which angle and velocity is recommended for performing the NHE? Think about anatomy, physiology and biomechanics, and along with athlete’s specific objectives, try to adapt accordingly the angle, velocity and flexion (or not) of the hip to provide the desired stimulus to the muscle.

Key words: eccentric exercise, Nordic hamstrings, muscle architecture, penneation angle, fascicle length.