Urinary N-terminal titin fragment concentration as a non-invasive biomarker of exercise-induced muscle damage in males and females.

Purpose: To examine the effects of muscle-damaging exercise on urinary N-terminal fragments of titin (UTF) in males and females, and its association with markers of exercise-induced muscle damage.

Methods: 27 males (n = 16) and females (n = 11) (height: 1.74 ± 0.10 m; body mass: 72.2 ± 11.4 kg; age: 22 ± 3 years) performed 200 eccentric contractions of the knee extensor on an isokinetic dynamometer. Urine and serum samples were collected pre-, post- and 48 h post-exercise to quantify UTF and creatine kinase (CK). Additionally, knee extensor maximal voluntary isometric force (MVIF), voluntary activation (VA), time to peak twitch (TTP), evoked maximal rate of force development (RFD), potentiated twitch force (Tw), and delayed-onset muscle soreness (DOMS) were recorded.

Results: UTF (2.3 ± 1.8 to 3.3 ± 3.4 nmol/mg/dL) and CK (9.7 ± 4.8 to 14.5 ± 8.7 units/L) concentrations were elevated 48 h after exercise (p < 0.01). DOMS was greater at all post-exercise time points vs. pre-exercise (p < 0.01). MVIF, evoked RFD, VA, and Tw all decreased after exercise (p < 0.01). The pre- to 48 h post-exercise change in UTF strongly correlated with CK (r = 0.73; p < 0.01), TTP (r = -0.77; p < 0.01) and evoked RFD (r = -0.62; p < 0.01) and moderately correlated with MVIF (r = -0.45; p < 0.01). Moderate strength correlations were found between the pre- to 48 h post-change in CK with DOMS (r = 0.47; p = 0.03). There were no sex differences for any variables (p > 0.05).

Conclusion: UTF was similarly increased post- and 48 h post-exercise in males and females and was moderately to strongly correlated to CK and some markers of neuromuscular function, but not DOMS.