Intestinal temperature does not reflect rectal temperature during prolonged, intense running with cold fluid ingestion.

It is generally assumed that intestinal temperature (Tint), as measured with a telemetric pill, agrees relatively well with rectal temperature (Trec) during exercise. However, whether Tint reflects Trec during prolonged, intense and continuous exercise when cold fluids are consumed is unknown. Therefore, we compared Trec and Tint during a half-marathon during which cold water was ingested to prevent bodyweight (BW) losses >2%. Nine endurance athletes (age 30 ± 5 years) underwent a 21.1 km running time-trial (TT) in the heat (~30 °C and 44% RH) while BW losses were maintained to ~1% with continuous cold (4 °C) water provision. Tint and Trec were monitored throughout the TT. Hypohydration level, TT time and fluid intake were 1.2 ± 0.4% BW, 93.2 ± 9.9 min and 2143 ± 264 ml, respectively. Trec was systematically higher than Tint by 0.25 °C (95% CI: 0.14-0.37 °C). Tint and Trec showed an excellent relative (r = 0.90, p < 0.01), but poor absolute agreement as reflected by a 95% limit of agreement of ±1.07 °C and a standard error of measurement of ±0.39 °C. In conclusion, Tint does not mirror Trec during prolonged, intense running with cold fluid ingestion and, therefore, these measures should not be used interchangeably under this scenario.

Sodium-induced hyperhydration decreases urine output and improves fluid balance compared with glycerol- and water-induced hyperhydration.

Before 2010, which is the year the World Anti-Doping Agency banned its use, glycerol was commonly used by athletes for hyperhydration purposes. Through its effect on osmoreceptors, we believe that sodium could prove a viable alternative to glycerol as a hyperhydrating agent. Therefore, this study compared the effects of sodium-induced hyperhydration (SIH), glycerol-induced hyperhydration (GIH) and water-induced hyperhydration (WIH) on fluid balance responses. Using a randomized, double-blind and counterbalanced protocol, 17 men (21 ± 3 years, 64 ± 6 kg fat-free mass (FFM)) underwent three 3-h hyperhydration protocols during which they ingested, over the first 60-min period, 30 mL/kg FFM of water with (i) an artificial sweetener (WIH); (ii) an artificial sweetener + 7.45 g/L of table salt (SIH); or (iii) an artificial sweetener + 1.4 g glycerol/kg FFM (GIH). Changes in body weight (BW), urine production, fluid retention, hemoglobin, hematocrit, plasma volume, and perceptual variables were monitored throughout the 3-h trials. After 3 h, SIH was associated with significantly (p < 0.05) lower hemoglobin, hematocrit (SIH: 43.1% ± 2.8%; GIH: 44.9% ± 2.4%), and urine production, as well as greater BW, fluid retention (SIH: 1144 ± 294 mL; GIH: 795 ± 337 mL), and plasma volume (SIH: 11.9% ± 12.0%; GIH: 4.0% ± 6.0%) gains, compared with GIH and WIH. No significant differences in heart rate or abdominal discomfort were observed between treatments. In conclusion, our results indicate that SIH is a superior hyperhydrating technique than, and proves to be a worthwhile alternative to, GIH.

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.

Pre-exercise hyperhydration-induced bodyweight gain does not alter prolonged treadmill running time-trial performance in warm ambient conditions.

This study compared the effect of pre-exercise hyperhydration (PEH) and pre-exercise euhydration (PEE) upon treadmill running time-trial (TT) performance in the heat. Six highly trained runners or triathletes underwent two 18 km TT runs (~28 °C, 25%-30% RH) on a motorized treadmill, in a randomized, crossover fashion, while being euhydrated or after hyperhydration with 26 mL/kg bodyweight (BW) of a 130 mmol/L sodium solution. Subjects then ran four successive 4.5 km blocks alternating between 2.5 km at 1% and 2 km at 6% gradient, while drinking a total of 7 mL/kg BW of a 6% sports drink solution (Gatorade, USA). PEH increased BW by 1.00 ± 0.34 kg (P < 0.01) and, compared with PEE, reduced BW loss from 3.1% ± 0.3% (EUH) to 1.4% ± 0.4% (HYP) (P < 0.01) during exercise. Running TT time did not differ between groups (PEH: 85.6 ± 11.6 min; PEE: 85.3 ± 9.6 min, P = 0.82). Heart rate (5 ± 1 beats/min) and rectal (0.3 ± 0.1 °C) and body (0.2 ± 0.1 °C) temperatures of PEE were higher than those of PEH (P < 0.05). There was no significant difference in abdominal discomfort and perceived exertion or heat stress between groups. Our results suggest that pre-exercise sodium-induced hyperhydration of a magnitude of 1 L does not alter 80-90 min running TT performance under warm conditions in highly-trained runners drinking ~500 mL sports drink during exercise.

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.

Effects of soya isoflavones and exercise on body composition and clinical risk factors of cardiovascular diseases in overweight postmenopausal women: a 6-month double-blind controlled trial.

Results from a pilot project indicate that isoflavones and exercise could have an additive effect on body composition and clinical risk factors of CVD in postmenopausal women. The objective of the present study was to assess the combined effect of exercise and isoflavones in overweight-to-obese postmenopausal women. In this double-blind randomised controlled trial, 100 overweight-to-obese (BMI 29·9 (sd 3·2) kg/m2) postmenopausal women were assigned to four groups: (1) placebo (PLA); (2) isoflavones (ISO); (3) exercise and placebo (Ex+PLA); (4) exercise and isoflavones (Ex+ISO). The supplementation contained 70 mg/d of isoflavones. Exercise consisted of three weekly sessions of resistance training and aerobics. Outcome measures included fat mass (FM), lean body mass (LBM), bone mineral density, lipid profile, fasting glucose, fasting insulin and insulin resistance (homeostasis assessment model). The main effects of exercise were observed for total FM (P = 0·02), FM% (P < 0·01), trunk FM% (P = 0·05), arm FM% (P < 0·01), leg FM% (P = 0·02), arm LBM (P < 0·01), leg LBM (P = 0·02) and C-reactive protein (P < 0·01). A main effect was detected for isoflavones in improving leg FM% (P = 0·05). No interactions were observed between isoflavones and exercise. In conclusion, it was observed that 6 months of exercise brought favourable changes in total FM, FM% and LBM in overweight postmenopausal women. No synergistic effects were observed between exercise and isoflavones. However, isoflavones could have a beneficial effect on leg FM%.