0206 Muscular damage can elicit metabolic and structural alterations in the affected fibers, including increased amino-acid turn-over. Urea is a well-known biochemical marker for amino-acid metabolism. PURPOSE: Given the similarities between sweat and blood plasma, this study aims to assess muscular damage induced by physical exercise through a non-invasive way by using sweat analysis. METHODS: 14 rugby players (male, 26±1 yrs, 87±4 kg, 48±2 ml·kg−1·min−1 VO2max) were studied. A continuous triangular cyclo-ergometric test was performed, using loads progressively increased by 25 W·min−1 until fatigue, to estimate VO2 from the heart rate and get the load in a rugby match. At the beginning of the sport season, a match was played by the subjects, which, being not well trained, suffered muscle damage. Before the match and 24, 48 and 72 h after the match ended, all subjects were having a sauna (81 °C and 87 % relative humidity). Sweat samples were taken from upper back skin (24 cm2), after the match was finished and after each sauna. Blood and urine samples were taken before each sauna and after the match. Sweat urea levels were expressed as cumulative concentration (mmol·L−1), and relative to the total estimated sweat volume (mmol) and body surface (mmol·m2). RESULTS: Exercise load during the match was estimated as 80% of VO2max (39±2 ml·kg−1·min−1). Creatine-kinase (CK) activity increased after 24 h (350±34 IU·L−1 vs. 140±23 IU·L−1 at rest, p<0.001), decreasing after 72 h towards resting values (160±22 IU·L−1). At rest, blood and urine urea levels were 5.3±0.5 and 351±30 mmol·L−1, respectively. In both cases a decrease was observed after 24 h (blood 3.8±0.3 mmol·L−1; urine 236±32 mmol·L−1, p<0.05), progressively increasing at 48 and 72 h. However, sweat urea concentration showed a delayed decay at 48 h (p<0.05). Sweat urea levels relative to sweat volume and body surface yielded a similar pattern to that of blood. To summarize, in parallel to a CK increase 24h after the match, blood, urine and sweat urea levels were significantly decreased. CONCLUSIONS: 1) Physical exercise causes important changes in blood, urine and sweat urea concentration, which could partly reflect metabolic changes attributable to muscle damage. 2) Normalization procedures in sweat analysis should be taken into account in order to standardize future non-invasive analytic procedures.