Post-training urinary titin fragment concentration increases in athletes with previous muscle strain injury: a pilot study in soccer players

Urinary titin fragment concentration has been established as a noninvasive biomarker of muscle protein degradation and muscle damage after exercise. We hypothesized that concerning the microdamage in the chronic phase of muscle strain injury, muscle damage is more likely to occur after exposure to training workload. We aimed to evaluate the urinary titin fragment concentration in professional soccer players who previously had muscle strain injuries (injured vs uninjured group: mean ± SEM age [years], 26.25 ± 1.4 vs 23.75 ± 1.01; playing years, 14.375 ± 1.17 vs 12.25 ± 0.24; height [cm], 173.63 ± 1.98 vs 176.38 ± 1.0; weight [kg], 69.63 ± 2.05 vs 72.38 ± 1.87; mean body mass index [kg/m2], 23.0 ± 0.32 vs 23.25 ± 1.39). The urine titin N-terminal fragments of eight professional soccer players with a previous muscle strain and eight uninjured players were measured using enzyme-linked immunosorbent assay before and 12 h after general team training. The urinary titin fragment values before and after training and the change in the titin fragment-to-creatinine fragment ratio were compared between the groups. The initial urinary titin fragment value did not significantly differ between the injured (from 18,457.96 ± 3,615.54 to 115,480.29 ± 26,462.36) and uninjured groups (from 23,119.47 ± 8,107.72 to 46,206.32 ± 9,833.77); however, the urine titin fragment value and change in the changes in urinary titin fragment ratio from before to after training were higher in the injured group (Wilcoxon rank-sum test, p < 0.05). These findings may help guide the future management of athletes with previous muscle strain injuries. Urine titin fragment values could be used to evaluate athletes with previous muscle injury.