Post-Exercise Rehydration in Athletes: Effects of Sodium and Carbohydrate in Commercial Hydration Beverages

he effects of varying sodium (Na) and carbohydrate (CHO) in oral rehydration solu- tions (ORS) and sports drinks (SD) for rehydration following exercise are unclear. We compared an ORS and SD for the percent of uid retained (%FR) following exercise-induced dehydration and hypothesized a more complete rehydration for the ORS (45 mmol Na/L and 2.5% CHO) and that the %FR for the ORS and SD (18 mmol Na/L and 6% CHO) would exceed the water placebo (W). A placebo-controlled, randomized, double-blind clinical trial was conducted. To induce 2.6% body mass loss (BML,p> 0.05 between treatments), 26 athletes performed three 90 min interval training ses- sions without drinking uids. Post-exercise, participants replaced 100% of BML and were observed for 3.5 h for the %FR. Mean SD for the %FR at 3.5 h was 58.1 12.6% (W), 73.9 10.9% (SD), and 76.9 8.0% (ORS). The %FR for the ORS and SD were similar and greater than the W (p< 0.05 ANOVA and Tukey HSD). Two-way ANOVA revealed a signi cant interaction with the ORS having greater suppression of urine production in the rst 60 min vs. W (SD did not differ from W). By 3.5 h, the ORS and SD promoted greater rehydration than did W, but the pattern of rehydration early in recovery favored the ORS. Keywords:carbohydrate; dehydration; oral

ANOVA and Tukey HSD). Two-way ANOVA revealed a signi cant interaction with the ORS having greater suppression of urine production in the rst 60 min vs. W (SD did not differ from W). By 3.5 h, the ORS and SD promoted greater rehydration than did W, but the pattern of rehydration early in recovery favored the ORS. Keywords:carbohydrate; dehydration; oral rehydration solution; sports drink; sodium 1. Introduction Inadequate uid intake during sports participation and training can lead to dehydra- tion. Persistent dehydration at or beyond 2% of body mass negatively impacts performance during subsequent efforts and increases the risks of heat illness [1,2]. Prompt and adequate rehydration between training sessions and competitions is important particularly when the period to rehydrate is brief before returning to physical and environmental challenges [1,3]. Rehydration is a function of gastric emptying, intestinal uid absorption, and retention of uid to restore body uid compartments. A comprehensive measure of these processes is the percentage of uid retained after a de ned recovery period following ingestion of a speci ed volume of uid [4,5]. To restore euhydration after exercise, ingesting from 125 to 150% of the volume lost has been recommended to offset urine losses during the recovery preceding subsequent exercise [1,6]. In research protocols, the de ned recovery is often 4–6 h long [5,7–13]; however, athletes often need to perform sooner than that. Additionally, ingesting substantial amounts of beverage can be discomforting and could impact performance when the calculated replacement volume is great [14]. Consequently, the composition of the rehydration beverage may play an especially important role when time is lacking for the rehydration process or ingestion of merely 100% of the sweat loss volume can be tolerated. The ingredients in a sports drink that promote rehydration include sodium (Na) and carbohydrate (CHO) with sodium being the primary factor [1,5,7,8,15,16]. Sodium helps maintain blood osmolality, which suppresses renal excretion of water and promotes uid Nutrients2023,15, 4759.

rehydration include sodium (Na) and carbohydrate (CHO) with sodium being the primary factor [1,5,7,8,15,16]. Sodium helps maintain blood osmolality, which suppresses renal excretion of water and promotes uid Nutrients2023,15, 4759.

Nutrients2023,15, 4759 2 of 13 retention [5]. Hydration beverages with Na concentration of at least 40 mmol/L have been shown to help restore Na balance in individuals who underwent exercise-induced dehydration [5,8]. Furthermore, beverages with 40 and 50 mmol/L Na promoted greater uid retention than beverages containing 31 mmol/L or less (p< 0.05) and produced retention similar to that of a 100 mmol/L beverage [5,8]. In these studies, beverages were either devoid of any carbohydrates [5] or the carbohydrate was maintained at 2% for all Na levels [8]. To date, other electrolytes such as potassium have not been demonstrated to have a clear effect on retention [4,16]. Carbohydrate content might also promote uid retention during rehydration by prolonging gastric emptying and intestinal absorption [1]. This effect is apparent when the beverage CHO content is high, in the range of 10 to 12% with a xed sodium content [9,10]. Beverages containing 10% CHO, well beyond that in sports drinks, have been reported to reduce plasma volume initially, likely due to slower gastric emptying because of the high energy density and/or osmolality of the hypertonic solution drawing water into the intestinal lumen from the serosal space [9]. Comparing beverages with Na xed at ~31–32 mmol/L, Evans et al. reported a 2% CHO beverage promoted greater plasma volume expansion within the rst hour of recovery vs. water or 10% CHO, suggesting enhanced absorption [9]. Ultimately, though, the 2% CHO beverage did not differ from the water placebo for uid retention at the end of the 6 h recovery. In contrast, the 10% CHO beverage outperformed water for uid retention by the 6 h mark [9]. The effect of varying CHO content in rehydration beverages having 6% or less CHO such as in sports drinks and oral rehydration solutions (ORS) is equivocal. Osterberg et al. found no difference in post-exercise rehydration uid retention (~75% of the ingested volume) for a 3% vs. 6% CHO [10]. Kamijo et al. reported that, during recovery after exercise, less urine was lost for a 6.5% CHO beverage vs. a 3.3% CHO beverage and water control, but the 3.3%

drinks and oral rehydration solutions (ORS) is equivocal. Osterberg et al. found no difference in post-exercise rehydration uid retention (~75% of the ingested volume) for a 3% vs. 6% CHO [10]. Kamijo et al. reported that, during recovery after exercise, less urine was lost for a 6.5% CHO beverage vs. a 3.3% CHO beverage and water control, but the 3.3% beverage also had less uid loss than the water trial [11]. The total percent retained was not reported, but the higher CHO beverage induced a greater uid balance based on urine loss. To rehydrate, participants in both studies ingested 100% of their exercise-induced weight loss and, while the CHO varied, the Na was xed at 18 mmol/L [10] or 21 mmol/L [11]. The question that remains is whether variations in CHO concentrations of between 2 and 6% enhance rehydration when Na content also varies in the beverage. A low- CHO, hypotonic beverage, i.e., ~2%, with a Na concentration above 40 mmol/L might promote equal or greater uid retention compared to a sports drink with 6% CHO and only 10–20 mmol/L of Na. Dumke's lab examined this and reported no difference in uid retention for an ORS (3.4% CHO and 60.9 mmol Na/L) or sports drink (6% CHO, 18 mmol Na/L) [17]. However, the protocol involved minimal dehydration (~1.2% of body mass) and the ingestion of 150% of weight loss before exercise was completed, and it lacked a placebo or water-control trial as a frame of reference for the unique protocol [17]. The lack of studies on this question hinders decision-making by athletes and recommendations by sports nutritionists regarding beverage selection to optimize rehydration particularly as athletes chose to limit dietary CHO. The purpose of the present study was to compare beverages that varied in both Na and CHO content within the range found in sports drinks for rehydration properties following exercise-induced dehydration in male athletes. The main outcome variable used to de ne completeness of rehydration was the percentage of uid retained during a 3.5 h period following beverage ingestion. To explore the effect of inversely varying Na and CHO,

beverages that varied in both Na and CHO content within the range found in sports drinks for rehydration properties following exercise-induced dehydration in male athletes. The main outcome variable used to de ne completeness of rehydration was the percentage of uid retained during a 3.5 h period following beverage ingestion. To explore the effect of inversely varying Na and CHO, two commercially available and commonly used rehydration beverages were administered in volumes that replaced 100% of the acute body weight loss. A water placebo was compared to an ORS containing 2.5% CHO and 45 mmol/L Na and a standard sports drink containing 6% CHO and 18 mmol/L Na. We hypothesized that the higher Na, lower CHO beverage would promote the greatest rehydration.

Nutrients2023,15, 4759 3 of 13 2. Materials and Methods 2.1. Subjects Physically t males of ages from 18 to 30 y were recruited. Females were excluded to avoid the potential effects of estrogen uctuations on water retention that might confound rehydration comparisons for the duration of testing a given subject [18]. The subject sample consisted of intercollegiate athletes, club sport athletes, several personal trainers, and several former military personnel, all of whom had to train regularly, i.e., >60 min a day at moderate to vigorous intensity, 3 d per week. All participants had to be free of any cardiovascular, metabolic, endocrine, or renal disease or dysfunction. Participants had to answer no to all seven questions on the PAR-Q, and each had to have a peak oxygen uptake (peak VO2) of 50 mL/kg/min. The study protocol was reviewed and approved by the institutional review board (no. 2013-0558), and written informed consent was obtained from each participant before testing. Physical characteristics are listed in Table. Table 1.Physical characteristics of the participants (n= 26). Characteristic Mean SD Age, y 21.0 3.0 Height, cm 177.8 7.0 Weight, kg 74.5 10.0 Body fat, % 13.1 4.0 TM peak VO 2, mL/kg/min 56.4 6.9 Body fat was determined using skinfolds. Peak VO2was measured using a metabolic cart (TrueOne 2400, Parvo Medics, Park City, UT, USA) during progressive resistance treadmill running. The running speed was 6–7 mph based on self-selection of the participant. After a two-minute warmup at 0% grade at the selected speed, the treadmill slope was increased by 1% every minute until volitional fatigue. An RER > 1.15, a heart rate within 10% of the age-predicted maximum, and a rating of perceived exertion 17 were used to con rm that maximum effort was delivered. 2.2. Experimental Design, Exercise Protocol, and Beverage Treatments A randomized counter-balanced crossover design with double blinding was used. Each of the three trials occurred at least 3 days apart. During the 24 h period prior to each 8 h experiment, participants ate the exact same diet and did not exercise. To ensure a standardized diet with consistent energy and sodium intake,

Experimental Design, Exercise Protocol, and Beverage Treatments A randomized counter-balanced crossover design with double blinding was used. Each of the three trials occurred at least 3 days apart. During the 24 h period prior to each 8 h experiment, participants ate the exact same diet and did not exercise. To ensure a standardized diet with consistent energy and sodium intake, participants were provided with identical foods for meals during the 24 h period and surveyed for physical activity and diet to con rm consistency of conditions prior to each experiment. A diagram of the protocol is presented in Figure. To induce dehydration, participants exercised during a ~90 min session composed of three 25 min periods of intermittent-intensity exercise performed indoors after a 2 min warm-up. Exercise occurred on a treadmill, stationary bike, and elliptical machine; the order of use of the exercise machines varied between participants but was the same for an individual for all trials. Each 25 min period consisted of a xed number of intervals at paces of walking (~3 mph), jogging (~7 mph), and running (10 mph), or the equivalent perceived intensities on the bike or elliptical machine (Table). Resistance settings for the bike and elliptical were identical for all three trials within a subject. A 5 min break was provided between periods for participants to dry off as needed, have body weight checked, and stretch.

Nutrients2023,15, 4759 4 of 13Nutrients 2023, 15, 4759 4 of 14 Figure 1. Sequence of the study protocol. Gray arrows indicate data collection times. Blue arrows during 60 min rehydration period indicate the percentage of volume ingested every 10 min. To induce dehydration, participants exercised during a ~90 min session composed of three 25 min periods of intermittent-intensity exercise performed indoors after a 2 min warm-up. Exercise occurred on a treadmill, stationary bike, and elliptical machine; the order of use of the exercise machines varied between participants but was the same for an individual for all trials. Each 25 min period consisted of a fixed number of intervals at paces of walking (~3 mph), jogging (~7 mph), and running (10 mph), or the equivalent perceived intensities on the bike or elliptical machine (Table 2). Resistance settings for the bike and elliptical were identical for all three trials within a subject. A 5 min break was provided between periods for participants to dry off as needed, have body weight checked, and stretch. Table 2. Intermittent Variable-Intensity Exercise Protocol. Phase Interval No. Intensity Duration Warm-up “Jog” 2 min Treadmill 1–5 Jog 1 min Walk 30 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Walk 30 s 5 min break Stationary cycle 2–10 Jog 1 min Walk 30 s Jog 40 s Sprint 20 s Jog 40 s Sprin t 20 s Jog 40 s Sprint 20 s Walk 30 s Figure 1. Sequence of the study protocol. Gray arrows indicate data collection times. Blue arrows during 60 min rehydration period indicate the percentage of volume ingested every 10 min. Table 2.Intermittent Variable-Intensity Exercise Protocol. Phase Interval No. Intensity Duration Warm-up “Jog” 2 min Treadmill 1–5 Jog 1 min Walk 30 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Walk 30 s 5 min break Stationary cycle 2–10 Jog 1 min Walk 30 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20

2 min Treadmill 1–5 Jog 1 min Walk 30 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Walk 30 s 5 min break Stationary cycle 2–10 Jog 1 min Walk 30 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Walk 30 s 5 min break Elliptical 11–15 Jog 1 min Walk 30 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Jog 40 s Sprint 20 s Walk 30 s Order of machine use was the same within a participant for all 3 trials but varied between subjects. During data collection on the nal six participants, a pilot study was conducted to explore the role of sodium balance on the completeness of rehydration. Sweat samples were obtained during the second 25 min period of exercise, after sweating was well established,

Nutrients2023,15, 4759 5 of 13 and analyzed for sodium concentration to estimate whole-body sodium loss during exercise. The collection technique has been used in prior rehydration studies [11] and is reliable but not without the potential to overestimate sweat sodium [19]. Just prior to resuming exercise, the forearm of each participant was sprayed thoroughly with distilled water to remove residual sodium on the skin and then thoroughly dried with a disposable, sodium-free towel. Immediately upon drying, a clear impermeable plastic bag was placed over the hand and forearm and secured with surgical tape to the inferior portion of the upper arm. At the end of that 25 min of exercise the bag was removed, and samples were analyzed immediately for sodium concentration. During the exercise-dehydration period, no uids were given to elicit a 2.5–3% re- duction in body mass. Environmental conditions ranged from 22 to 29 C (71 to 85 F) and from 13 to 43% relative humidity. Following exercise completion, participants were weighed and rested for 45 min before consuming a volume of the beverage that replaced 100% of body mass lost. Beverages were ingested in six aliquots over a 1 h period given at the end of the trial. Speci cally, 25% of the total volume was ingested every 10 min for the rst 20 min; thereafter, 12.5% of the volume was ingested at four 10 min intervals. The composition of the beverages is presented in Table. Table 3.Composition of Beverage Treatments. Water Placebo ORS Sports Drink Energy, Cal/L ~2.5 (CIT, MD) 100 240 Osmolality, mOsm/kg 0 270 330–380 CHO, g% 0 2.5% (GLU) 6.0% (SUC, GLU) Sodium, mmol/L 0.33 45 (NaCl, Na-CIT) 18 (NaCl, Na-CIT) Chloride, mmol/L 0 34 (NaCl) 11 (NaCl) Potassium, mmol/L 0 20 (K-CIT) 3 (KH 2PO 4) Zinc, mmol/L 0 0.12 (Zn-GLUC) 0 Nutrition form or source in parentheses. CIT: citrate; MD: maltodextrin; GLU: glucose; SUC: sucrose; Na: sodium; Cl: chloride; KH2PO4: potassium phosphate; GLUC: gluconate. Each participant ingested a water placebo (with avored powder, private label version of Crystal Lite ® (Signature Brand, Itasca, IL, USA), ORS (Pedialyte ® , Columbus, OH,

3 (KH 2PO 4) Zinc, mmol/L 0 0.12 (Zn-GLUC) 0 Nutrition form or source in parentheses. CIT: citrate; MD: maltodextrin; GLU: glucose; SUC: sucrose; Na: sodium; Cl: chloride; KH2PO4: potassium phosphate; GLUC: gluconate. Each participant ingested a water placebo (with avored powder, private label version of Crystal Lite ® (Signature Brand, Itasca, IL, USA), ORS (Pedialyte ® , Columbus, OH, USA), or sports drink (Gatorade ® , Chicago, IL, USA) during one of the three experimental sessions to replace 100% of the body mass lost and were compared for uid retention. All beverages were grape- avored, purple in color, and administered in opaque cups to prevent drawing attention to the beverage differences. Beverages, which were served at room temperature, were prepared according to the manufacturers' specs by a colleague who was not involved in any of the data collection or beverage administration for blinding purposes. 2.3. Analyses and Computations Retention of ingested uid was determined by measuring the mass of urine excreted at complete voids at minutes 30, 60, 135, and 210 after beverage ingestion. Body mass was measured at the 60- and 210-min time points, after urine collection. Between measurements, other than when they walked to the rest room or scale for data collection, participants remained seated and watched movies, worked on computers, or read self-selected materials. The amount of beverage provided to rehydrate participants and the amount of urine produced during the 3.5 h recovery period was weighed on a calibrated analytical balance that measured uid mass to within 0.02 g (ICS439-SW digital scale, Mettler-Toledo, Toledo, OH, USA). Body mass was measured to within 0.001 kg using a calibrated industrial scale (ICS439-SW digital scale, Mettler-Toledo, Toledo, OH, USA). The coef cient of variation for triplicate measures for the range of pre-exercise body masses within a subject was 0.005–0.009%. The change in body mass at the various times of measurement indicated the extent of uid loss and replacement needed for the subsequent rehydration. For all weight measurements, participants were measured in the nude behind a curtain with the

This study compares rehydration properties of beverages with different sodium and carbohydrate content in athletes.