*2.3. Urinary Damage Markers*

## 2.3.1. Urinary Cystatin C (uCyst-C)

Since Cyst-C is freely filtered by the glomerulus, reabsorbed and metabolized in the renal tubule, even a small elevation of urinary Cyst-C (uCyst-C) reflects proximal tubule injury [13].

Bongers et al. studied subjects performing submaximal exercise at an 80% HR rate and found a significant increase in uCyst-C with higher values after prolonged exercise (150 min) compared to acute (30 min) exercise [26]. In 2012, the same authors studied urinary markers after single and repetitive bouts of exercise. They examined participants of the International Four Day Marches Nijmegen. Subjects walked at 70% intensity over 30, 40 or 50 km for 3 consecutive days. Bongers studied several

urinary markers and found that uCyst-C increased 1.8 times after the first day (from 0.05 to 0.09 mg/L), but this effect disappeared on day 3 (uCyst-C = 0.06 mg/L) [44]. Interestingly, in these studies, uCyst-C was measured mainly to normalize uKIM-1 and uNGAL levels [26,44]. The increase in uCyst-C was also found by Wolyniec after 10 and 100 km runs. There was a 2.56-fold increase after 10 km and a 4.96-fold increase after 100 km. When normalized to creatinine, these increases were 1.39- and 1.95-fold, respectively [45].

The number of studies coming from only two centers is small, but it seems that uCyst-C is a very sensitive marker of proximal tubule dysfunction after exercise.
