Human physiological responses to cold-water immersion: acute and repeated exposures

Investigations regarding both acute and repeated cold-water immersions are limited. Most importantly, there is a paucity of information pertaining to the impact of such exposures on whole-body fluid distribution and plasma constituents. Furthermore, previous studies have not differentiated between the hydrostatic and thermal effects of water immersion. males participated in a warm-water stress test (WWST), and a 15-d cold water acclimation programme, with cold-water stress tests (CWST) on days 1, 8 and 15, and 90-min cold-water immersions at rest on intervening days. Stress tests were 90 min in duration (60 min seated rest, 30 min cycling at 1 watt-kg"1). The WWST and first CWST comparison allowed the hydrostatic and thermal differentiation, while repeated influences were determined from the CWST comparisons. Measurements during the stress tests included body-fluid volumes (radionuclides and Evan's blue dye), plasma constituents (haematocrit, haemoglobin, electrolytes, osmolality, protein, hormones), core and skin temperatures, cardiac frequency, oxygen consumption, and skin blood flow. the rest phase of the WWST, plasma volume (PV) underwent an hydrostatically-induced elevation (12%), which appeared to be due to an influx of intracellular water. This intravascular fluid shift was not evident during the CWST , and was possibly countered by thermally-induced venoconstriction. Furthermore, increased plasma atrial natriuretic peptide concentration during the CWST was uniquely shown to be a response to the cold temperature, rather than the hydrostatic effects of immersion, since it remained constant during the WWST . The increased PV during the WWST subsided during the exercise period, but remained above pre-immersion levels, possibly due to a redistribution of blood from the central volume to exercising muscles. Repeated cold-water immersion produced an habituated-thermogenic response during the resting phase of the final CWST , compared to CWST1 (12.18 ml.kg-1.min-1 reduction), which was not accompanied by an hypothermic core-temperature response. While there was a 3.2% reduction in pre-immersion total body water, and an attenuated decrease in PV during the resting phase of CWST3 , habituation did not result in significant changes in body-fluid distribution or plasma constituents, at rest or during exercise across the CWST days.