Professional football players have some particular physiological characteristics which allow them to run an average of 10-12 km per match as well as reaching speeds above 30 km/h. This makes those muscle groups with higher involvement in acceleration and deceleration scenarios (such as the hamstrings) be more susceptible to injury (they represent 12-16 % of total injuries).
One of the reasons why this area is more sensitive to getting injured could be related to the composition of its muscle fibres. The hamstrings have a high proportion of type II fibres, also called fast fibres,1 and due to structural and metabolic differences with respect to type I fibres, make them more vulnerable to damage from mechanical stress.2 That’s why if we know how these types of muscle fibre respond to workload, it could help prevent injuries.
Traditional blood tests which measure biomarkers, such as creatine kinase (CK), relate muscle response (specifically, muscle damage) to training load in football players,3 but the information it provides is limited and its reading does not differentiate between the types of fibre. A new study performed by researchers from the University of Barcelona,4 has shown how the concentration of fast and slow isoforms of myosin in blood could be a reliable marker for exercise-induced muscle damage, as well as being capable to differentiate by fibre type. Following this study, fast myosin isoform would be a characteristic of type II fibres, while the slow ones are type I fibres. Carmona et al. have seen that after an exercise with a high eccentric component, performed with an isoinertial device, the levels of fast myosin increase, while in endurance sports, such as an ultra-marathon, the levels of slow isoform increase; thus, this technique can distinguish between types of fibres and sports specialisation.5,6
It is well worth to highlight that isoform analysis can be sensitive when detecting first-degree muscle strains (small fibres breaking) that are difficult to diagnose through magnetic resonance imaging or ultrasound. Another aspect to have in consideration is that the traditional laboratory technique (Western blot) used to analyse myosin isoforms, is slow and not very sensitive, so it is not possible to implement it in a practical way for elite sports.
For this reason, research performed by members of FC Barcelona and the University of Barcelona,7 have used a faster and more precise technique (ELISA), rather than the traditional methods, by measuring myosin levels in the blood for Sporting de Gijón club throughout a season. Also, the concentrations of CK and lactate dehydrogenase (LDH) were measured in order to compare the evolution of myosin with that of biomarkers traditionally used for monitoring players.