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00005768-200805001-0152400005768_2008_40_s190_klau_appearance_5miscellaneous< 16_0_1_0 >Medicine & Science in Sports & Exercise©2008The American College of Sports MedicineVolume 40(5) Supplement 1May 2008p S190Appearance of Deuterium Oxide in Sweat During Cycling at 29°C: 1347: Board #86 May 28 9:30 AM - 11:00 AM[A-27 Free Communication/Poster - Heat Stress and Fluid Balance: Hydration Status and Sodium Balance: MAY 28, 2008 7:30 AM - 12:30 PM: ROOM: Hall B]Klau, Jennifer F.1; Ganio, Matthew S.1; Lee, Elaine C.1; Yeargin, Susan W.2; McDermott, Brendon P.1; Van Heest, Jaci L.1; Maresh, Carl M. FACSM1; Armstrong, Lawrence E. FACSM11University of Connecticut, Storrs, CT. 2Indiana State University, Terre Haute, IN.Email: jennifer.klau@uconn.edu(No relationships reported)Sweat production and evaporation are essential to human heat dissipation during exercise. The path of fluid movement from mouth to sweat glands is well known; its temporal course is not.PURPOSE: The purpose of this study was to determine the elapsed time from consumption of fluid to appearance as sweat on the forehead and on the central back.METHODS: We used an oral deuterium oxide (D2O) bolus to trace the elapsed time from the point of fluid consumption to its appearance in sweat, on the forehead and the central back. Fifteen well-trained male cyclists (age 27.1± 5.8 y; 179.2± 3.7 cm; 73.11±7.31 kg; maximal aerobic power (VO2max) 60.43±6.79 ml·kg min−1) ingested bolus of D2O (0.15mg·kg −1 body mass) and rode on a cycle ergometer, alternating 60% VO2max and 75% VO2max every 15 min for 120 min in a warm environment. Sweat samples were collected at min 10, 15, 20, 30 and 40 on the back; at sweat onset, min 20 and min 40 on the forehead. Samples were analyzed for D2O content by isotope ratio mass spectrometerspectroscopy, after preparation as described by Davis et al.RESULTS: All samples contained D2O at sweat onset (mean onset 13.0 ± 4.4 min). One-way analysis of variance identified significant (P<.05) (a) differences of D2O between minutes 20 and 40 on the forehead, and (b) a main effect of time. D2O change on the central back was correlated (P<.05) with maximal sweat rate (r2 = 0.88).CONCLUSION: These results suggest that ingested fluid moves rapidly from mouth to sweat in 10 min or less during cycling. This unique discovery further supports the importance of fluid intake during exercise for thermoregulation.Appearance of Deuterium Oxide in Sweat During Cycling at 29°C: 1347: Board #86 May 28 9:30 AM - 11:00 AMKlau, Jennifer F.; Ganio, Matthew S.; Lee, Elaine C.; Yeargin, Susan W.; McDermott, Brendon P.; Van Heest, Jaci L.; Maresh, Carl M. FACSM; Armstrong, Lawrence E. FACSMA-27 Free Communication/Poster - Heat Stress and Fluid Balance: Hydration Status and Sodium Balance: MAY 28, 2008 7:30 AM - 12:30 PM: ROOM: Hall B540