Running Title: Glycerol hyperhydration during cold air exposure Correspondence:

Hypohydration occurs during cold air exposure (CAE) through combined effects of reduced fluid intake and increased fluid losses. Since hypohydration is associated with reduced physical performance, strategies for maintaining hydration during CAE are important. Glycerol ingestion (GI) can induce hyperhydration in hot and temperate environments, resulting in greater fluid retention compared to water (WI) alone, but is not effective during cold water immersion. Water immersion induces a greater natriuresis and diuresis than cold exposure; therefore, whether GI might be effective for hyperhydration during cold air exposure remains unknown. This study examined physiological responses, i.e., thermoregulatory, cardiovascular, renal, vascular fluid and fluid-regulating hormonal responses, to GI in seven men during 4 h CAE (15oC, 30 % rh). Subjects completed three separate, double-blind and counterbalanced trials including: WI (37 ml waterL total body water-1); GI (37 ml waterL total body water-1 plus 1.5 g glycerolL total body water-1); and no fluid (NF). Fluids were ingested 30 min before CAE. Thermoregulatory responses to cold were similar during each trial. Urine flow rates were higher (p=0.0001) with WI (peak 11.8 mlmin-1, SD 1.9) than GI (5.0 mlmin-1, SD 1.8), and fluid retention was greater (p=0.0001) with GI (34%, SD 7) than WI (18%, SD 5) at the end of CAE. Differences in urine flow rate and fluid retention were the result of a greater free water clearance with WI. These data indicate glycerol can be an effective hyperhydrating agent during CAE