CORE™ wearable sensor: Comparison against gastrointestinal temperature during cold water ingestion and a 5 km running time-trial.

Five km running time-trials (TT) are associated with rapid and significant increases in core body temperature (TC). For such races, real-time feedback from pre-exercise and exercise TC may be helpful in the design of an optimal pacing strategy aimed at limiting the possibility of developing heat-related illnesses. This study compared measurements of TC obtained with a wearable device, the CORE™, to those of a gastrointestinal pill (GI pill), during cold water ingestion and a 5 km running TT. Twelve participants (25 ± 4 yrs) ingested 7.5 mL/kg fat-free mass of 4 °C water over the first 5 min of a 120 min sitting period, after which they completed a 5 km running TT at 30 °C, 50% relative humidity. A TC difference > ± 0.25 °C between sensors was deemed clinically unacceptable. Prior to water ingestion, the CORE-derived TC was 0.49 ± 0.25 °C lower than the GI pill. The CORE was irresponsive to the 0.26 ± 0.22 °C peak decline in TC captured with the GI pill 40 min following water ingestion. Prior to the TT, TC was 0.30 ± 0.25 °C lower with the CORE than the GI pill. During the TT, the CORE underestimated the rate of increase in TC by 0.0125 ± 0.019 °C/min compared with the GI pill, and mean absolute difference in TC between sensors was of 0.47 ± 0.34 °C. In conclusion, the CORE does not capture the cooling effect of cold water ingestion and provides a clinically relevant underestimation of TC during a 5 km running TT in the heat.

Impact of dehydration on perceived exertion during endurance exercise: A systematic review with meta-analysis.

Background: Understanding the impact of stressors on the rating of perceived exertion (RPE) is relevant from a performance and exercise adherence/participation standpoint. Athletes and recreationally active individuals dehydrate during exercise. No attempt has been made to systematically determine the impact of exercise-induced dehydration (EID) on RPE. Objective: The present meta-analysis aimed to determine the effect of EID on RPE during endurance exercise and examine the moderating effect of potential confounders. Data analyses: Performed on raw RPE values using random-effects models weighted mean effect summaries and meta-regressions with robust standard errors, and with a practical meaningful effect set at 1 point difference between euhydration (EUH) and EID. Only controlled crossover studies measuring RPE with a Borg scale in healthy adults performing ≥30 min of continuous endurance exercise while dehydrating or drinking to maintain EUH were included. Results: Sixteen studies were included, representing 147 individuals. Mean body mass loss with EUH was 0.5 ± 0.4%, compared to 2.3 ± 0.5% with EID (range 1.7-3.1%). Within an EID of 0.5-3% body mass, a maximum difference in RPE of 0.81 points (95% CI: 0.36-1.27) was observed between conditions. A meta-regression revealed that RPE increases by 0.21 points for each 1% increase in EID (95% CI: 0.12-0.31). Humidity, ambient temperature and aerobic capacity did not alter the relationship between EID and RPE. Conclusion: Therefore, the effect of EID on RPE is unlikely to be practically meaningful until a body mass loss of at least 3%.

The ability of exercise to meaningfully improve glucose tolerance in people living with prediabetes: A meta-analysis.

BACKGROUND: Individuals with prediabetes are likely to progress to Type 2 diabetes. Although exercise training is an established method to improve glycemic control, the degree to which this translates into meaningful improvements, particularly in individuals with prediabetes, is unclear. The purpose of this meta-analysis was to investigate the ability of exercise training to improve 2-hour glucose tolerance beyond the smallest worthwhile difference in individuals with prediabetes. It was hypothesized that the majority of implemented exercise programs designed for individuals with prediabetes would not result in meaningful improvements in glucose tolerance. METHODS: Searches were performed in MEDLINE, The Cumulative Index to Nursing and Allied Health Literature, SPORTDiscus, and the Cochrane Library. Included studies reported glucose tolerance using a 2-hour oral glucose tolerance test at baseline and post-intervention; implemented an exercise program lasting at least 12 weeks; and included adults living with prediabetes. Mean effect summaries were determined using random-effects models. Magnitude-based inference statistic was used to estimate the likelihood that observed changes in glucose tolerance were meaningful to patients. RESULTS: Nine articles were included in the meta-analysis, producing 12 independent exercise interventions. The interventions led to an average improvement in glucose tolerance of 5.9% (95% confidence interval: 3.7%-8.0%). Seven (58%) exercise interventions were deemed likely to benefit patients, whereas five (42%) had trivial or unclear findings. CONCLUSION: While exercise intervention led to statistically significant improvements in 2-hour glucose tolerance, the benefit for individuals living with prediabetes remains unclear. Further research is needed to delineate optimal prescription parameters for generating meaningful benefits in glucose tolerance.

Permanent tattooing has no impact on local sweat rate, sweat sodium concentration and skin temperature or prediction of whole-body sweat sodium concentration during moderate-intensity cycling in a warm environment.

PURPOSES: This study investigated the impact of permanently tattooed skin on local sweat rate, sweat sodium concentration and skin temperature and determined whether tattoos alter the relationship between local and whole-body sweat sodium concentration. METHODS: Thirteen tattooed men (27 ± 6 years) completed a 1 h (66 ± 4% of [Formula: see text]) cycling trial at 32 °C, 35% relative humidity. Sweat rate and sweat sodium concentration were measured using the whole-body washdown and local absorbent patch techniques. Patches and skin-temperature probes were applied over the right/left thighs and tattooed/non-tattooed (contralateral) regions. RESULTS: Local sweat rates did not differ (p > 0.05) between the right (1.11 ± 0.38) and left (1.21 ± 0.37) thighs and the permanently tattooed (1.93 ± 0.82) and non-tattooed (1.72 ± 0.81 mg cm-2 min-1) regions. There were no differences in local sweat sodium concentration between the right (58.2 ± 19.4) and left (55.4 ± 20.3) thighs and the permanently tattooed (73.0 ± 22.9) and non-tattooed (70.2 ± 18.9 mmol L-1) regions. Difference in local skin temperature between the right and left thighs (- 0.043) was similar to that between the permanently tattooed and non-tattooed (- 0.023 °C) regions. Prediction of whole-body sweat sodium concentration for the permanently tattooed (41.0 ± 6.7) and the non-tattooed (40.2 ± 5.3 mmol L-1) regions did not differ. CONCLUSION: Permanent tattoos do not alter local sweat rate, sweat sodium concentration or local skin temperature during moderate-intensity cycling exercise in a warm environment. Results from a patch placed over a tattooed surface correctly predicts whole-body sweat sodium concentration from an equation developed from a non-tattooed region.

Validity and Reliability of the CorTempTM Telemetric Pill during 50 h of Reuse in a Circulating Water Bath.

It has been shown that CorTempTM telemetric pills (CTTPs) provide valid measures of rectal temperature when used as suppositories. While encapsulated into a condom linked to a thread, CTTPs can be inserted in and extracted from the rectum and be reused. The validity and reliability of the CTTP throughout repeated use remains to be demonstrated. Three CTTPs were compared to a YSI 401 wired rectal probe inside a circulating water bath (temperatures varying from 36.5 to 39.4 °C) during 50 h of intermittent use. Each CTTP underwent 20 trials comprising 6 protocols of varying duration: 6 · 1 h, 5 · 2 h, 4 · 3 h, 3 · 4 h and 2 · 5 h. All CTTPs were washed, switched off and disinfected after each trial to reproduce real-life use. Acceptable agreement between sensors was taken as a mean bias within ±0.27 °C. None of the pills showed signs of deterioration following 50 h of reuse. As for relative validity, where all CTTPs showed robust coefficients of determination ranging from 0.98 to 0.99, absolute validity was excellent with each CTTP showing mean biases and typical errors of the estimate (TEE) within ±0.27 °C. Comparisons between the first and last trial each CTTP underwent resulted in means biases and TEEs within ±0.27 °C and coefficients of determination ranging from 0.97 to 0.99, which indicates strong absolute and relative reliability. The present results show that CTTPs can provide valid and reliable measurements of temperature when reused up to 50 h.

Wireless measurement of rectal temperature during exercise: Comparing an ingestible thermometric telemetric pill used as a suppository against a conventional rectal probe.

Wireless measurement of rectal temperature during exercise may circumvent some limitations associated with the use of a conventional wired probe. We determined, for the first time, whether temperatures provided in vivo by wireless ingestible thermometric telemetric pills and a rectal probe compare favorably under conditions producing slow and rapid increases and decreases in rectal temperature. While wearing a rectal probe linked to a wireless ingestible thermometric telemetric pill, 13 participants completed the following phases: 1) 30 min sitting; 2) 45 min passive heat exposure (40-42 °C); 3) 45 min sitting while ingesting 7.5 g of ice slurry · kg body mass-1; 4) running exercise (38 °C) at 68% V˙O2max until a 39.5 °C increase in rectal probe temperature and; 5) cold-water (10 °C) immersion until a 1.5 °C decrease in rectal probe temperature. Acceptable differences between devices were taken as ≤ 0.3 °C. Mean differences within phases were all < 0.3 °C, whereas 95% limits of agreement ranged from ±0.2 °C to ±0.4 °C, coefficient of variations from ±0.3% to ±0.6% and typical error of measurements from ±0.1 °C to ±0.2°. Of the 14881 rectal temperature values measured over the experiment with the wireless ingestible thermometric telemetric pills and rectal probe, 91% of the differences between devices were found to be ≤ 0.3 °C. Results suggest that rectal temperatures provided by a wireless ingestible thermometric telemetric pill used as a suppository agree with those of a conventional wired probe. Hence, rectal temperature can reliably be measured using a wireless ingestible thermometric telemetric pill as a suppository.

Salt + Glycerol-Induced Hyperhydration Enhances Fluid Retention More Than Salt- or Glycerol-Induced Hyperhydration.

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.

Impact of Mild Hypohydration on Muscle Endurance, Power, and Strength in Healthy, Active Older Men.

Goulet, EDB, Mélançon, MO, Lafrenière, D, Paquin, J, Maltais, M, and Morais, JA. Impact of mild hypohydration on muscle endurance, power, and strength in healthy, active older men. J Strength Cond Res 32(12): 3414-3424, 2018-Under particular circumstances older persons may be vulnerable to developing mild chronic hypohydration. In young adults, hypohydration has been shown to impair muscle endurance, power and strength. Muscle performance declines with aging, a condition known as dynapenia. How hypohydration impacts muscle performance in older persons remains unclear. In this study, we examined this question, believing it may identify a factor exacerbating dynapenia. One-hour after having been passively exposed to heat where either a body mass loss of 1% was induced or euhydration maintained with fluid ingestion, 8 healthy, active older men (age: 68 ± 5 years) completed an exercise testing session where indices of muscle strength (30-second chair stand, grip strength, maximal isometric seated leg-press extension), endurance (seated leg-curl flexion + seated leg-press extension to exhaustion at 60% of 1 repetition maximum), and power (30-second Wingate test) were assessed. Gastrointestinal temperature before exercise testing was not significantly different from that measured before heat exposure with neither hydration regimen. Magnitude-based inferential statistics indicate that from a clinical perspective, the effect of hypohydration on 30-second chair stand (-1.0 ± 4.4%) is possibly harmful, for grip strength (-2.4 ± 4.1%), lower limbs endurance (-7.5 ± 11.2%), and anaerobic power (-3.9 ± 4.3%) likely detrimental, and unclear with respect to maximal isometric lower limb strength. Maintaining adequate hydration in older men is important, since hypohydration of only 1% body mass could impede muscle endurance, power and strength and, consequently, worsen the impact of dynapenia.

Sweat Sodium Concentration: Inter-Unit Variability of a Low Cost, Portable, and Battery Operated Sodium Analyzer.

The B-722 Laqua Twin is a low cost, portable, and battery operated sodium analyzer, which can be used for the assessment of sweat sodium concentration. The Laqua Twin is reliable and provides a degree of accuracy similar to more expensive analyzers; however, its interunit measurement error remains unknown. The purpose of this study was to compare the sodium concentration values of 70 sweat samples measured using three different Laqua Twin units. Mean absolute errors, random errors and constant errors among the different Laqua Twins ranged respectively between 1.7 mmol/L to 3.5 mmol/L, 2.5 mmol/L to 3.7 mmol/L and -0.6 mmol/L to 3.9 mmol/L. Proportional errors among Laqua Twins were all < 2%. Based on a within-subject biological variability in sweat sodium concentration of ± 12%, the maximal allowable imprecision among instruments was considered to be £ 6%. In that respect, the within (2.9%), between (4.5%), and total (5.4%) measurement error coefficient of variations were all < 6%. For a given sweat sodium concentration value, the largest observed difference in mean and lower and upper bound error of measurements among instruments were, respectively, 4.7 mmol/L, 2.3 mmol/L, and 7.0 mmol/L. In conclusion, our findings show that the interunit measurement error of the B-722 Laqua Twin is low and methodologically acceptable.

Comparison of Sodium Chloride Tablets-Induced, Sodium Chloride Solution-Induced, and Glycerol-Induced Hyperhydration on Fluid Balance Responses in Healthy Men.

Savoie, FA, Asselin, A, and Goulet, EDB. Comparison of sodium chloride tablets-induced, sodium chloride solution-induced, and glycerol-induced hyperhydration on fluid balance responses in healthy men. J Strength Cond Res 30(10): 2880-2891, 2016-Sodium chloride solution-induced hyperhydration (NaCl-SolIH) is a powerful strategy to increase body water before exercise. However, NaCl-SolIH is associated with an unpleasant salty taste, potentially dissuading some athletes from using it and coaches from recommending it. Therefore, we evaluated the hyperhydrating potential of sodium chloride tablets-induced hyperhydration (NaCl-TabIH), which bypasses the palatability issue of NaCl-SolIH without sacrificing sodium chloride content, and compared it to NaCl-SolIH and glycerol-induced hyperhydration (GIH). Sixteen healthy males (age: 21 ± 2 years; fat-free mass (FFM): 65 ± 6 kg) underwent three, 3-hour long passive hyperhydration protocols during which they drank, over the first 60 minutes, 30-ml·kg FFM of an artificially sweetened solution. During NaCl-TabIH, participants swallowed 7.5, 1 g each, sodium chloride tablets with every liter of solution. During NaCl-SolIH, an equal quantity of sodium chloride tablets was dissolved in each liter of solution. With GIH, the glycerol concentration was 46.7 g·L. Urine production, fluid retention, hemoglobin, hematocrit, plasma volume, and perceptual variables were monitored throughout the trials. Total fluid intake was 1948 ± 182 ml. After 3 hour, there were no significant differences among treatments for hemoglobin, hematocrit, and plasma volume changes. Fluid retention was significantly greater with NaCl-SolIH (1150 ± 287 ml) than NaCl-TabIH (905 ± 340 ml) or GIH (800 ± 211 ml), with no difference between NaCl-TabIH and GIH. No differences were found among treatments for perceptual variables. NaCl-TabIH and GIH are equally effective, but inferior than NaCl-SolIH. NaCl-TabIH represents an alternative to hyperhydration induced with glycerol, which is prohibited by the World Anti-Doping Agency.

Half-marathon running performance is not improved by a rate of fluid intake above that dictated by thirst sensation in trained distance runners.

PURPOSE: It has been demonstrated that exercise-induced dehydration (EID) does not impair, and ad libitum drinking optimizes, cycling time-trial (TT) performance. However, the idea that EID ≥ 2 % bodyweight (BW) impairs endurance performance is well ingrained. No study has tested the impact of EID upon running TT performance. We compared the effects of thirst-driven (TD) vs. programmed fluid intake (PFI) aimed at maintaining EID-associated BW loss <2 % on half-marathon performance. METHODS: Ten trained distance runners underwent, in a randomized, crossover fashion, two, 21.1 km running TTs on a treadmill (30 °C, 42 % relative humidity) while facing a wind speed matching running speed and drinking water (1) according to thirst sensation (TD) or (2) to maintain BW loss <2 % of their pre-exercise BW (PFI), as recommended by the American College of Sports Medicine. RESULTS: Despite that PFI significantly reduced EID from 3.1 ± 0.6 (TD) to 1.3 ± 0.7 % BW (PFI), mean rectal temperature from 39.4 ± 0.4 to 39.1 ± 0.3 °C, mean body temperature from 38.1 ± 0.4 to 37.7 ± 0.2 °C and mean heart rate from 175 ± 9 to 171 ± 8 bpm, neither half-marathon time (TD 89.8 ± 7.7; PFI 89.6 ± 7.7 min) nor running pace (TD 4.3 ± 0.4; PFI 4.2 ± 0.4 min/km) differed significantly between trials. CONCLUSION: Albeit providing trivial cardiovascular and thermoregulatory advantages, in trained distance runners, PFI (1,380 ± 320 mL/h) offers no performance benefits over TD fluid intake (384 ± 180 mL/h) during a half-marathon raced under warm conditions.

Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure.

OBJECTIVE: It is purported that exercise-induced dehydration (EID), especially if ≥ 2% bodyweight, impairs endurance performance (EP). Field research shows that athletes can achieve outstanding EP while dehydrated > 2% bodyweight. Using the meta-analytic procedure, this study compared the findings of laboratory-based studies that examined the impact of EID upon EP using either ecologically valid (EV) (time-trial exercise) or non-ecologically valid (NEV) (clamped-intensity exercise) exercise protocols. METHODS: EP outcomes were put on the same scale and represent % changes in power output between euhydrated and dehydrated exercise tests. Random-effects model meta-regressions and weighted mean effect summaries, mixed-effects model analogue to the ANOVAs and magnitude-based effect statistics were used to delineate treatment effects. MAIN RESULTS: Fifteen research articles were included, producing 28 effect estimates, representing 122 subjects. Compared with euhydration, EID increased (0.09±2.60%, (p=0.9)) EP under time-trial exercise conditions, whereas it reduced it (1.91±1.53%, (p<0.05)) with NEV exercise protocols. Only with NEV exercise protocols did EID ≥ 2% body weight impair EP (p=0.03). CONCLUSIONS: Evidence indicates that (1) EID ≤ 4% bodyweight is very unlikely to impair EP under real-world exercise conditions (time-trial type exercise) and; (2) under situations of fixed-exercise intensity, which may have some relevance for military and occupational settings, EID ≥ 2% bodyweight is associated with a reduction in endurance capacity. The 2% bodyweight loss rule has been established from findings of studies using NEV exercise protocols and does not apply to out-of-doors exercise conditions. Athletes are therefore encouraged to drink according to thirst during exercise.

Effects of quercetin supplementation on endurance performance and maximal oxygen consumption: a meta-analysis.

Lately, the effect of quercetin supplementation (QS) on endurance performance (EP) and maximal oxygen consumption (VO2max) has been receiving much scientific and media attention. Therefore, a meta-analysis was performed to determine QS's ergogenic value on these variables. Studies were located with database searches (PubMed and SPORTDiscus) and cross-referencing. Outcomes represent mean percentage changes in EP (measured via power output) and VO2max between QS and placebo. Random-effects model meta-regression, mixed-effects model analog to the ANOVA, random-effects weighted mean effect summary, and magnitude-based inferences analyses were used to delineate the effects of QS. Seven research articles (representing 288 subjects) were included, producing 4 VO2max and 10 EP effect estimates. Mean QS daily intake and duration were, respectively, 960 ± 127 mg and 26 ± 24 d for the EP outcome and 1,000 ± 0 mg and 8 ± 23 d for the VO2max outcome. EP was assessed during exercise with a mean duration of 79 ± 82 min. Overall, QS improved EP by 0.74% (95% CI: 0.10-1.39, p = .02) compared with placebo. However, only in untrained individuals (0.83% ± 0.78%, p = .02) did QS significantly improve EP (trained individuals: 0.09% ± 2.15%, p = .92). There was no relationship between QS duration and EP (p = .69). Overall, QS increased VO2max by 1.94% (95% CI: 0.30-3.59, p = .02). Magnitude-based inferences suggest that the effect of QS on EP and VO2max is likely to be trivial for both trained and untrained individuals. In conclusion, this meta-analysis indicates that QS is unlikely to prove ergogenic for aerobic-oriented exercises in trained and untrained individuals.

Effect of electric fan use in isolation or combined with ice slurry/cold water ingestion and lower-leg immersion in young men during intermittent physical activity in hot-humid conditions.

Using a randomized crossover protocol, 10 young men completed four 180 min exposures (38 °C, 60% relative humidity), alternating between 30 min of walking and 30 min of sitting where fluid or ice slurry were served. Participants underwent four trials: (i) 5 mL·kg body mass-1 of 20 °C water (CON); (ii) 5 mL·kg body mass-1 of 20 °C water + fan at 4 m·s-1 (FAN); (iii) fan + 3 mL·kg body mass-1 of ice slurry + 2 mL·kg body mass-1 of 4 °C water (FAN + ISCW); and (iv) FAN + ISCW + lower-leg immersion in 20 °C water (FAN + ISCW + LLI). Sweat and body mass losses were higher with FAN than CON, FAN + ISCW, and FAN + ISCW + LLI. Mean and peak changes in Δrectal temperature, heart rate, and perceived heat and thirst from baseline were not statistically and practically different between FAN and CON. FAN + ISCW + LLI decreased sweat loss compared with FAN + ISCW and mean and peak changes in Δrectal temperature, heart rate, and perceived thirst compared with CON. FAN + ISCW + LLI also attenuated the changes in Δrectal temperature (peak) and thirst (mean and peak) compared with FAN. In conclusion, FAN slightly exacerbates fluid loss but does not attenuate the changes in Δrectal temperature, heart rate, and perceived heat and thirst during intermittent physical activity in hot-humid conditions. However, coupling ISCW or ISCW + LLI with the use of a fan attenuates the increase in these outcomes compared with no intervention and to a greater extent for rectal temperature and thirst when fan is coupled with ISCW + LLI than when it is used in isolation.

Change in heart rate variability during two firefighting work cycles.

This study aimed to determine whether the change in heart rate variability from pre to post firefighting is modulated by different work cycles. Thirteen male firefighters underwent two firefighting simulations that comprised two identical 25-min work bouts intercalated by a passive recovery period of either 20 min (T20) or 5 min (T5). The square root of the mean squared differences of successive R-R intervals (RMSSD) and aural temperature were measured at rest before (PRE) and after (POST) firefighting simulations. The decrease in RMSSD was different between firefighting simulations (T20: -10 ± 21.2 ms, T5: -19.9 ± 20.9 ms, interaction, p = 0.02). Post-firefighting aural temperature was greater (p = 0.05) in T5 (37.18 ± 0.53 °C) than in T20 (36.88 ± 0.49 °C). In conclusion, a shorter recovery period of 5 min between firefighting work bouts decreases post-firefighting heart rate variability, possibly attributed to a lower parasympathetic reactivation and a higher absolute value of body temperature.

Effect of Glycerol-Induced Hyperhydration on a 5-kilometer Running Time-Trial Performance in the Heat in Recreationally Active Individuals.

Maximal oxygen consumption (V˙O2max) is a major determinant of 5-km running time-trial (TT) performance. Glycerol-induced hyperhydration (GIH) could improve V˙O2max in recreationally active persons through an optimal increase in plasma volume. Moreover, ingestion of a large bolus of cold fluid before exercise could decrease thermal stress during exercise, potentially contributing to improved performance. We determined the effect of GIH on 5-km running TT performance in 10 recreationally active individuals (age: 24 ± 4 years; V˙O2max: 48 ± 3 mL/kg/min). Using a randomized and counterbalanced protocol, participants underwent two, 120-min hydration protocols where they ingested a 1) 30 mL/kg fat-free mass (FFM) of cold water (~4 °C) with an artificial sweetener + 1.4 g glycerol/kg FFM over the first 60 min (GIH) or 2) 7.5 mL/kg FFM of cold water with an artificial sweetener over the first 20 min (EUH). Following GIH and EUH, participants underwent a 5-km running TT at 30 °C and 50% relative humidity. After 120 min, GIH was associated with significantly greater fluid retention (846 ± 415 mL) and plasma volume changes (10.1 ± 8.4%) than EUH, but gastrointestinal (GI) temperature did not differ. During exercise, 5-km running TT performance (GIH: 22.95 ± 2.62; EUH: 22.52 ± 2.74 min), as well as heart rate, GI temperature and perceived exertion did not significantly differ between conditions. This study demonstrates that the additional body water and plasma volume gains provided by GIH do not improve 5-km running TT performance in the heat in recreationally active individuals.

Repeatability of Ad Libitum Water Intake during Repeated 1 h Walking/Jogging Exercise Sessions Conducted under Hot Ambient Conditions.

A drinking strategy aiming to replace a given percentage of the sweat losses incurred during exercise should result in reproducible fluid intake volume and, hence, fluid balance from one exercise session to the other performed under similar scenarios. Whether this may also be the case with ad libitum drinking during exercise is unclear. We characterized the repeatability of ad libitum water intake during repeated 1 h exercise sessions and examined its effect over time on fluid balance and selected physiological functions and perceptual sensations. Twelve (3 women) healthy individuals participated in this study. At weekly intervals, they completed four 2 × 30 min walking/jogging exercise bouts (55% V˙O2max, 40 °C, 20-30% relative humidity) interspersed by a 3 min recovery period. During exercise, participants consumed water (20 °C) ad libitum. There were no significant differences among the four exercise sessions for absolute water intake volume (~1000 mL·h-1), percent body mass loss (~0.4%), sweat rate (~1300 mL·h-1) and percent of sweat loss replaced by water intake (~80%). Heart rate, rectal temperature, and perceived thirst and heat stress did not differ significantly between the first and fourth exercise sessions. Perceived exertion was significantly lower during the fourth vs. the first exercise session, but the difference was trivial (<1 arbitrary unit). In conclusion, ad libitum water intake during four successive identical 1 h walking/jogging sessions conducted in the heat will result in similar water intake volumes and perturbations in fluid balance, heart rate, rectal temperature, and perceived thirst, heat stress and exertion.

Validity and reliability of the Horiba C-122 compact sodium analyzer in sweat samples of athletes.

Accurate sodium replacement during prolonged exercise is possible when sweat rate and sweat sodium content are directly measured. Few athletes have access to sweat sodium content measurement, as the equipment needed to perform such analyzes is costly, laboratory-based or requires technical skills. Using 70 sweat samples collected in 24 athletes from 3 anatomical sites, this study determined the reliability [single-trial and inter-day (7 samples over 3 days)] and validity (instrument error) of a pocket-sized, easy-to-use and low cost sodium analyzer (Horiba C-122, Kyoto, Japan) against reference values of an ion chromatograph, the 883 Basic IC plus (Metrohm AG, Herisau, Switzerland). The Horiba C-122 showed high single-trial reliability with an intraclass correlation coefficient (ICC) of 0.997, a typical error of measurement (EM) of 1.77 mmol/L and a coefficient of variation (CV) of 3.73%. As expected, the reliability of the 883 Basic IC plus was superior to that of the Horiba C-122 (ICC: 0.999; typical EM: 0.70 mmol/L; CV: 1.52%). The Horiba's C-122 inter-day reliability was high (ICC: 1.00; typical EM: 0.35 mmol/L). An ICC of 0.975 indicates there was a strong relationship between results provided by both analyzers. Compared with reference values, the Horiba C-122 demonstrated a mean bias of 1.71 mmol/L, a pure EM of 7.52 mmol/L and 68% limits of agreement ranging from -5.81 to 9.23 mmol/L. We propose that the Horiba C-122 is sufficiently reliable to be used under field conditions where some degree of imprecision is acceptable, but not for research purposes where high accuracy is required.

Effect of Pre-Exercise Caffeine Intake on Endurance Performance and Core Temperature Regulation During Exercise in the Heat: A Systematic Review with Meta-Analysis.

BACKGROUND: Heat is associated with physiological strain and endurance performance (EP) impairments. Studies have investigated the impact of caffeine intake upon EP and core temperature (CT) in the heat, but results are conflicting. There is a need to systematically determine the impact of pre-exercise caffeine intake in the heat. OBJECTIVE: To use a meta-analytical approach to determine the effect of pre-exercise caffeine intake on EP and CT in the heat. DESIGN: Systematic review with meta-analysis. DATA SOURCES: Four databases and cross-referencing. DATA ANALYSIS: Weighted mean effect summaries using robust variance random-effects models for EP and CT, as well as robust variance meta-regressions to explore confounders. STUDY SELECTION: Placebo-controlled, randomized studies in adults (≥ 18 years old) with caffeine intake at least 30 min before endurance exercise ≥ 30 min, performed in ambient conditions ≥ 27 °C. RESULTS: Respectively six and 12 studies examined caffeine's impact on EP and CT, representing 52 and 205 endurance-trained individuals. On average, 6 mg/kg body mass of caffeine were taken 1 h before exercises of ~ 70 min conducted at 34 °C and 47% relative humidity. Caffeine supplementation non-significantly improved EP by 2.1 ± 0.8% (95% CI - 0.7 to 4.8) and significantly increased the rate of change in CT by 0.10 ± 0.03 °C/h (95% CI 0.02 to 0.19), compared with the ingestion of a placebo. CONCLUSION: Caffeine ingestion of 6 mg/kg body mass ~ 1 h before exercise in the heat may provide a worthwhile improvement in EP, is unlikely to be deleterious to EP, and trivially increases the rate of change in CT.

Cognitive Performance Before and Following Habituation to Exercise-Induced Hypohydration of 2 and 4% Body Mass in Physically Active Individuals.

We investigated the effect of repeated exposures to hypohydration upon cognitive performance. In a randomized crossover design, ten physically active adults completed two 4-week training blocks, one where they maintained euhydration (EUH) and the other where they were water-restricted (DEH) during walking/running at 55% V.O2max, 40 °C. Three sessions per week were performed: (1) 1 h of exercise, (2) exercise until 2% or (3) 4% of body mass has been lost or replaced. Limited to the first and fourth training week, a 12 min walking/running time-trial was completed following the 2 and 4% exercise bouts. Trail making, the Wisconsin card sort, the Stop signal task, Simple visual reaction time and Corsi block-tapping tests were performed immediately following the time-trials. Body mass loss was maintained < 1% with EUH and reached 2.7 and 4.7% with DEH following the time-trials. Except for a lower percentage of correct responses (% accuracy) during the Wisconsin card sort test (p < 0.05) with DEH compared to EUH, no statistically significant decline in cognitive performance was induced by low and moderate levels of hypohydration. Compared to week 1, no statistical differences in cognitive responses were observed after repeated exposures to hypohydration (all p > 0.05). From a practical perspective, the gains in cognitive performance following training to DEH were mostly unclear, but under certain circumstances, were greater than when EUH was maintained. Based on the battery of cognitive tests used in the current study, we conclude that whether physically active individuals are habituated or not to its effect, exercise-induced hypohydration of 2 and 4% has, in general, no or unclear impact on cognitive performance immediately following exercise. These results encourage further research in this area.