Objectives: To determine changes in common urinary markers of hydration maintained by the drivers (mushers) during a wilderness endurance event in the arctic and to determine water turnover in this select group of individuals.
Study design: During this descriptive study, data was systematically collected on hydration, water turnover, changes in resting and exercise heart rate, fatigue and rating of perceived exertion during an arduous dogsled race in the arctic.
Methods: Sixteen mushers were recruited for the study, 13 of whom completed the entire race. At five different checkpoints along the 1049-mile trail (symbolic distance), urine was collected. Urine osmolality (U(osm)) was determined using freezing point depression. Urine specific gravity (U(sg)) was determined using a hand-held refractometer. Water turnover was measured in 5 mushers from rates of deuterium (2H2O) elimination (rH2O). Prior to the start of the race, and at five checkpoints along the trail, a resting heart rate, fatigue rating scale and a rating of perceived exertion (RPE), were collected.
Results: Out of the 13 subjects that completed the event, four of the mushers had a U(sg) > or = 1.030 (mean 1.023 +/- 0.007) at some point during the event. Ten had a urine osmolality > or = 900 mOsm L(-1) at some point during the event, with an average U(osm) of 868 +/- 277 mOsm L(-1) over the duration of the event. Water turnover demonstrated that rH2O averaged 2.85 +/- 1.18 ml kg(-1) day(-1) (range 2.03 -4.60) over the duration of the event. Resting heart rate increased significantly over the course of the race. The RPE was related to the overall fatigue rating scale.
Conclusions: These data demonstrate that the majority of mushers studied showed signs of dehydration based on common urinary markers during the long-distance dogsled race. The dehydration appears to have had an influence on the resting heart rate, overall fatigue and the rating of perceived exertion during the race.