Metabolic Habituation Following Repeated Resting Cold-Water Immersion Is Not Apparent During Low-Intensity Cold-Water Exercise.

Abstract

This project examined the effects of repeated, resting cold-water immersion on metabolic heat production and core temperature defence during subsequent rest and exercising immersions. Seven males undertook 15 days of cold-water adaptation, immersed to the fourth intercostal space, with cold-water stress tests (CWST) on days 1, 8 and 15 (18.1 SD 0.1°C: 60 min seated, followed by 30 min cycling (1 W·kg -1 )), and 90-min resting immersions (18.4 SD 0.4°C) on each of the intervening days. Adaptation elicited an habituated thermogenic response during the rest phase of CWST3 beyond 20 min, compared to CWST1 (P<0.05), with oxygen consumption averaging 11.15 (± 0.25) ml·kg -1 ·min -1 and 8.61 (± 0.90) ml·kg -1 ·min -1 by 50 min, for CWST1 and CWST3, respectively. During exercise, this metabolic blunting was only apparent over the first 10-min period (60-70 min). No significant differences were observed during either the rest or exercise phases of the CWSTs for oesophageal temperature (T es ). While repeated coldwater exposures produced an habituated-thermogenic response, for an equivalent drop in T es during rest, neither this response, nor an elevated thermogenesis, were apparent during subsequent cold-water exercise.

Cold-water acclimation does not modify whole-body fluid regulation during subsequent cold-water immersion

“…This fluid movement is independent of water temperature, at least within the range 18-33°C, and the movement of plasma fluid ). The current data from CWST2 and CWST3 are entirely consistent with this pattern, and reveal that cold-water acclimation, which elicited an habituated thermogenic response in these subjects (Stocks et al 2001), did not significantly modify wholebody fluid regulation during subsequent cold-water immersion. Furthermore, acclimation did not evoke significant changes in plasma osmolality, total protein, electrolyte, ANP or aldosterone concentrations, relative to that observed in the unacclimated state.…”

“…During CWST1 all subjects experienced significant thermal strain, as summarised by the following changes, which occurred over the whole immersion (0-60 min) and are reported in detail elsewhere (Stocks et al 2001: oesophageal temperature: À0.6 (0.1)°C; mean skin temperature: À7.4 (0.5)°C; oxygen uptake +0.5 (0.04) l min À1 . However, TBW was not altered during CWST1 (P>0.05, /<0.20; Fig.…”

“…After 60 min of rest, subjects cycled for an additional 30 min. However, these data were not used within the current study, but have been reported elsewhere (Stocks et al 2001). Acclimation immersions occurred on each intervening day (2-7 and 9-14), and were 90-min immersions in the same posture [18.4 (0.4)°C, air temperature 21.3 (1.0)°C].…”

“…Cardiac frequency was recorded at 0.2 Hz (Polar Electro SportTester, model PE3000; Finland), and oxygen uptake was measured every 10 min during immersion over a 3-min period (Q-Plex I, Quinton Instrument, Seattle, Wash., USA). These measures are more fully described and reported elsewhere (Stocks et al 2001, and do not form a central focus of this project.…”

Ethnic differences in thermoregulation: Genotypic versus phenotypic heat adaptation

“…One might therefore assume that homeostatic systems optimising energy efficiency, in parallel with body temperature regulation, would tend to favour heat conservation over heat production. In fact, the habituated metabolic reaction, once thought to be unique to Australian Aborigines, can readily be induced in cold-adapted Caucasians (Davis, 1961;Golden and Tipton, 1988;Stocks et al, 2001). Accordingly, it appears, at least superficially, that the metabolic response of Aborigines may simply be attributable, at least in part, to physiological adaptation, rather than solely to phylogenetic differences.…”