Hydroxylysine excretion does not indicate collagen damage with downhill running in young men.

The purpose of this study was to determine whether urinary excretion of hydroxylysine (HO-Lys) is increased following prolonged, predominantly downhill running. Such an increase would be evidence of exercise-induced collagen damage. Each of ten young men performed a treadmill running test to determine VO2peak (an approximation of VO2max) followed by 60 min of intermittent running on -10% slope. Total urine excreted from 48 h pre-exercise to 96h post-exercise was collected in 8-h samples for measurement of HO-Lys. In addition, both urinary 3-methylhistidine (3-MeHis) excretion and serum creatine kinase (SCK) activity were measured as indicators of muscle tissue damage. In no sampling period was post-exercise HO-Lys excretion altered compared with pre-exercise (e.g., pre-exercise: 82.2 +/- 9.6 mumol.24 h-1, mean +/- SE; 51.0 +/- 3.7 mumol.g creatinine-1; post-exercise: 72.9 +/- 2.0 mumol.24 h-1; 47.0 +/- 1.5 mumol.g creatinine-1). SCK activity was increased (346%) 24 h post-exercise, but not immediately, 48 h, or 72 h post-exercise. 3-MeHis excretion was not altered following exercise. There were no strong associations between HO-Lys excretion and either of the markers of muscle damage. We concluded that no evidence of exercise-induced collagen damage was provided by urinary HO-Lys excretion.