No abstract

Hyperhydration has been demonstrated to improve work capacity and cardiovascular and thermoregulatory functions, enhance orthostatic tolerance, slow or neutralize bone demineralization, and decrease postdive bubble formation. Adding sodium or glycerol to a hyperhydration solution optimizes fluid retention. Sodium and glycerol produce their effect through different physiological mechanisms. If combined into a hyperhydration solution, their impact on fluid retention could potentially be greater than their singular effect. We compared the effect of salt-induced hyperhydration (SIH), glycerol-induced hyperhydration (GIH), and salt + glycerol-induced hyperhydration (SGIH) on fluid balance responses during a 3-hr passive experiment. Using a randomized, crossover, and counterbalanced experiment, 15 young men (22 ± 4 years) underwent three, 3-hr hyperhydration experiments during which they ingested 30 ml/kg fat-free mass (FFM) of water with an artificial sweetener plus either (a) 7.5 g of table salt/L (SIH), (b) 1.4 g glycerol/kg FFM (GIH), or (c) 7.5 g of table salt/L + 1.4 g glycerol/kg FFM (SGIH). After 3 hr, there were no significant differences in plasma volume changes among experiments (SIH: 11.3% ± 9.9%; GIH: 7.6% ± 12.7%; SGIH: 11.3% ± 13.7%). Total urine production was significantly lower (SIH: 775 ± 329 ml; GIH: 1,248 ± 270 ml; SGIH: 551 ± 208 ml) and fluid retention higher (SIH: 1,127 ± 212 ml; GIH: 729 ± 115 ml; SGIH: 1,435 ± 140 ml) with SGIH than either GIH or SIH. Abdominal discomfort was low and not significantly different among experiments. In conclusion, results show that SGIH reduces urine production and provides more fluid retention than either SIH or GIH.

Sweat sodium concentration (SSC) can be determined using different analytical techniques (ATs), which may have implications for athletes and scientists. This study compared the SSC measured with 5 ATs: ion chromatography (IChr), flame photometry (FP), direct (DISE) and indirect (IISE) ion-selective electrode, and ion conductivity (IC). Seventy sweat samples collected from 14 athletes were analyzed with 5 instruments: the 883 Basic IC Plus (IChr, reference instrument), AAnalyst 200 (FP), Cobas 6000 (IISE), Sweat-Chek (IC), and B-722 Laqua Twin (DISE). Instruments showed excellent relative (intraclass correlation coefficient (ICC) ≥ 0.999) and absolute (coefficient of variation (CV) ≤ 2.6%) reliability. Relative validity was also excellent between ATs (ICC ≥ 0.961). In regards to the inter-AT absolute validity, compared with IChr, standard error of the estimates were similar among ATs (2.8-3.8 mmol/L), but CV was lowest with DISE (3.9%), intermediate with IISE (7.6%), and FP (6.9%) and highest with IC (12.3%). In conclusion, SSC varies depending on the AT used to analyze samples. Therefore, results obtained from different ATs are scarcely comparable and should not be used interchangeably. Nevertheless, taking into account the normal variability in SSC (∼±12%), the imprecision of the recommendations deriving from FP, IISE, IC, and DISE should have trivial health and physiological consequences under most exercise circumstances.

No abstract

Gastrointestinal temperature (Tgint) measurement with a telemetric pill (TP) is increasingly used in exercise science. Contact of cool water with a TP invalidates Tgint assessment. However, what effect a heat sink created in the proximity of a TP may have on the assessment of Tgint remains unknown. We examined the impact of an ice slurry-induced heat sink on Tgint and rectal temperature (Trec) following exercise. After 20 min of seating (20–22 °C, 25–40% relative humidity (RH)), 11 men completed two intersperse exercise periods (31–32 °C, 35% RH) at 75–80% of estimated maximal heart rate until a Trec increase of 1 °C above baseline level. Following the first exercise period, participants were seated for 45 min and ingested 7.5 g·kg−1 of thermoneutral water, whereas, following the second period, they ingested 7.5 g·kg−1 of ice slurry. Both Tgint and Trec were measured continuously. The TPs were swallowed 10 h prior to the experiments. A bias ≤0.27 °C was taken as an indication that Tgint and Trec provided similar core temperature indices. Mean biases and 95% limits of agreement during passive sitting, first exercise, water ingestion, second exercise, and ice slurry ingestion periods were 0.16 ± 0.53, 0.13 ± 0.41, 0.21 ± 0.70, 0.17 ± 0.50, and 0.18 ± 0.66 °C, respectively. The rates of decrease in Tgint and Trec did not differ between the water and ice slurry ingestion periods. Our results indicate that ice slurry ingestion following exercise does not impact TP-derived assessment of Tgint compared with Trec.