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

## TL;DR

This study shows that a urinary protein fragment called UTF can be a non-invasive indicator of muscle damage after exercise in both men and women.

## Contribution

The study introduces UTF as a non-invasive biomarker for exercise-induced muscle damage with strong correlations to traditional markers like CK.

## Key findings

- UTF and CK levels increased significantly 48 hours after muscle-damaging exercise.
- UTF showed strong correlations with CK and neuromuscular function markers but not with muscle soreness.
- No sex differences were observed in UTF or other measured variables.

## Abstract

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.

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 (RFDmax), potentiated twitch force (Twpot), and delayed-onset muscle soreness (DOMS) were recorded.

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 RFDmax, VA, and Twpot all decreased after exercise (p < 0.01). The pre- to 48 h post-exercise change in UTF strongly correlated with CK (rs = 0.73; p < 0.01), TTP (rs = -0.77; p < 0.01) and evoked RFDmax (rs = -0.62; p < 0.01) and moderately correlated with MVIF (rs = -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).

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.

The online version contains supplementary material available at 10.1007/s00421-025-05936-6.