Protein requirements may be lower on a training compared to rest day but are not influenced by moderate training volumes in endurance trained males.

The impact of training volume on protein requirements in endurance trained males was investigated with indicator amino acid oxidation (IAAO) methodology on a recovery day (REST) or after a 10 or 20 km run while consuming a single suboptimal protein intake (0.93 g/kg/day). Phenylalanine excretion (F13CO2; inverse proxy for whole body protein synthesis) was greatest and phenylalanine net balance was lowest on REST compared to post-exercise recovery with no difference between training volumes. Single point F13CO2 was indistinguishable from past IAAO studies using multiple protein intakes. Our results suggest that protein requirements may be greatest on recovery days but are not influenced by moderate training volumes in endurance athletes.

Greater plasma essential amino acids and lower 3-methylhistidine with higher protein intake during endurance training: a randomised control trial.

Endurance exercise alters amino acid (AA) metabolism that necessitates greater AA intake in the post exercise recovery period to support recovery. Thus, daily AA ingestion during a period of endurance training may affect the metabolically active plasma free AA pool, which is otherwise maintained during periods of inadequate protein intake by the breakdown of skeletal muscle proteins. Nine endurance-trained males completed a 4-day running protocol (20 km, 5 km, 10 km and 20 km on days 1-4, respectively) on three occasions with a controlled diet providing different protein intakes [0.94(LOW), 1.20(MOD) or 1.83gprotein kgbody mass-1 day-1 (HIGH)]. Urine collected over 24 h on day-4 and plasma collected after an overnight fast on day-5 were analyzed for free AA (plasma) and 3-methylhistidine (3MH; plasma and urine), a marker of myofibrillar protein breakdown. There was an effect of protein intake (HIGH > MOD/LOW; P < 0.05) on fasted plasma essential AA, branched chain AA and 3MH but no effect on 24-h urinary 3-MH excretion. Consuming a previously determined optimal daily protein intake of 1.83 g kg-1 day-1 during endurance training maintains fasted plasma free AA and may attenuate myofibrillar protein catabolism, although this latter effect was not detected in 24-h urinary excretion. The maintenance of the metabolically active free plasma AA pool may support greater recovery from exercise and contribute to the previously determined greater whole-body net protein balance in this athletic population. TRN: NCT02801344 (June 15, 2016).

Protein Intake to Maximize Whole-Body Anabolism during Postexercise Recovery in Resistance-Trained Men with High Habitual Intakes is Severalfold Greater than the Current Recommended Dietary Allowance.

BACKGROUND: Dietary protein supports resistance exercise-induced anabolism primarily via the stimulation of protein synthesis rates. The indicator amino acid oxidation (IAAO) technique provides a noninvasive estimate of the protein intake that maximizes whole-body protein synthesis rates and net protein balance. OBJECTIVE: We utilized IAAO to determine the maximal anabolic response to postexercise protein ingestion in resistance-trained men. METHODS: Seven resistance-trained men (mean ± SD age 24 ± 3 y; weight 80 ± 9 kg; 11 ± 5% body fat; habitual protein intake 2.3 ± 0.6 g·kg-1·d-1) performed a bout of whole-body resistance exercise prior to ingesting hourly mixed meals, which provided a variable amount of protein (0.20-3.00 g·kg-1·d-1) as crystalline amino acids modeled after egg protein. Steady-state protein kinetics were modeled with oral l-[1-13C]-phenylalanine. Breath and urine samples were taken at isotopic steady state to determine phenylalanine flux (PheRa), phenylalanine excretion (F13CO2; reciprocal of protein synthesis), and net balance (protein synthesis - PheRa). Total amino acid oxidation was estimated from the ratio of urinary urea and creatinine. RESULTS: Mixed model biphasic linear regression revealed a plateau in F13CO2 (mean: 2.00; 95% CI: 1.62, 2.38 g protein·kg-1·d-1) (r2 = 0.64; P Ë‚ 0.01) and in net balance (mean: 2.01; 95% CI: 1.44, 2.57 g protein·kg-1·d-1) (r2 = 0.63; P Ë‚ 0.01). Ratios of urinary urea and creatinine concentrations increased linearly (r = 0.84; P Ë‚ 0.01) across the range of protein intakes. CONCLUSIONS: A breakpoint protein intake of ∼2.0 g·kg-1·d-1, which maximized whole-body anabolism in resistance-trained men after exercise, is greater than previous IAAO-derived estimates for nonexercising men and is at the upper range of current general protein recommendations for athletes. The capacity to enhance whole-body net balance may be greater than previously suggested to maximize muscle protein synthesis in resistance-trained athletes accustomed to a high habitual protein intake. This trial was registered at clinicaltrials.gov as NCT03696264.

Protein to Maximize Whole-Body Anabolism in Resistance-trained Females after Exercise.

INTRODUCTION: Current athlete-specific protein recommendations are based almost exclusively on research in males. PURPOSE: Using the minimally invasive indicator amino acid oxidation technique, we determined the daily protein intake that maximizes whole-body protein synthesis (PS) and net protein balance (NB) after exercise in strength-trained females. METHODS: Eight resistance-trained females (23 ± 3.5 yr, 67.0 ± 7.7 kg, 163.3 ± 3.7 cm, 24.4% ± 6.9% body fat; mean ± SD) completed a 2-d controlled diet during the luteal phase before performing an acute bout of whole-body resistance exercise. During recovery, participants consumed eight hourly meals providing a randomized test protein intake (0.2-2.9 g·kg·d) as crystalline amino acids modeled after egg protein, with constant phenylalanine (30.5 mg·kg·d) and excess tyrosine (40.0 mg·kg·d) intakes. Steady-state whole-body phenylalanine rate of appearance (Ra), oxidation (Ox; the reciprocal of PS), and NB (PS - Ra) were determined from oral [C] phenylalanine ingestion. Total protein oxidation was estimated from the urinary urea-creatinine ratio (U/Cr). RESULTS: A mixed model biphase linear regression revealed a break point (i.e., estimated average requirement) of 1.49 ± 0.44 g·kg·d (mean ± 95% confidence interval) in Ox (r = 0.64) and 1.53 ± 0.32 g·kg·d in NB (r = 0.65), indicating a saturation in whole-body anabolism. U/Cr increased linearly with protein intake (r = 0.56, P < 0.01). CONCLUSIONS: Findings from this investigation indicate that the safe protein intake (upper 95% confidence interval) to maximize anabolism and minimize protein oxidation for strength-trained females during the early ~8-h postexercise recovery period is at the upper end of the recommendations of the American College of Sports Medicine for athletes (i.e., 1.2-2.0 g·kg·d).

The Effect of Dietary Protein on Protein Metabolism and Performance in Endurance-trained Males.

Recommendations for dietary protein are primarily based on intakes that maintain nitrogen (i.e., protein) balance rather than optimize metabolism and/or performance. PURPOSE: This study aimed to determine how varying protein intakes, including a new tracer-derived safe intake, alter whole body protein metabolism and exercise performance during training. METHODS: Using a double-blind randomized crossover design, 10 male endurance-trained runners (age, 32 ± 8 yr; V˙O2peak, 65.9 ± 7.9 mL O2·kg·min) performed three trials consisting of 4 d of controlled training (20, 5, 10, and 20 km·d, respectively) while consuming diets providing 0.94 (LOW), 1.20 (MOD), and 1.83 (HIGH) g protein·kg·d. Whole body protein synthesis, breakdown, and net balance were determined by oral [N]glycine on the first and last day of the 4-d controlled training period, whereas exercise performance was determined from maximum voluntary isometric contraction, 5-km time trial, and countermovement jump impulse (IMP) and peak force before and immediately after the 4-d intervention. RESULTS: Synthesis and breakdown were not affected by protein intake, whereas net balance showed a dose-response (HIGH > MOD > LOW, P < 0.05) with only HIGH being in positive balance (P < 0.05). There was a trend (P = 0.06) toward an interaction in 5-km Time Trial with HIGH having a moderate effect over LOW (effect size = 0.57) and small effect over MOD (effect size = 0.26). IMP decreased with time (P < 0.01) with no effect of protein (P = 0.56). There was no effect of protein intake (P ≥ 0.06) on maximum voluntary isometric contraction, IMP, or peak force performance. CONCLUSION: Our data suggest that athletes who consume dietary protein toward the upper end of the current recommendations by the American College of Sports Medicine (1.2-2 g·kg) would better maintain protein metabolism and potentially exercise performance during training.

Whole-body net protein balance plateaus in response to increasing protein intakes during post-exercise recovery in adults and adolescents.

BACKGROUND: Muscle protein synthesis and muscle net balance plateau after moderate protein ingestion in adults. However, it has been suggested that there is no practical limit to the anabolic response of whole-body net balance to dietary protein. Moreover, limited research has addressed the anabolic response to dietary protein in adolescents. The present study determined whether whole-body net balance plateaued in response to increasing protein intakes during post-exercise recovery and whether there were age- and/or sex-related dimorphisms in the anabolic response. METHODS: Thirteen adults [7 males (M), 6 females (F)] and 14 adolescents [7 males (AM), 7 females (AF) within ~ 0.4 y from peak height velocity] performed ~ 1 h variable intensity exercise (i.e., Loughborough Intermittent Shuttle Test) prior to ingesting hourly mixed meals that provided a variable amount of protein (0.02-0.25 g·kg- 1·h- 1) as crystalline amino acids modeled after egg protein. Steady-state protein kinetics were modeled noninvasively with oral L-[1-13C]phenylalanine. Breath and urine samples were taken at plateau to determine phenylalanine oxidation and flux (estimate of protein breakdown), respectively. Whole-body net balance was determined by the difference between protein synthesis (flux - oxidation) and protein breakdown. Total amino acid oxidation was estimated from the ratio of urinary urea/creatinine. RESULTS: Mixed model biphasic linear regression explained a greater proportion of net balance variance than linear regression (all, r 2 ≥ 0.56; P < 0.01), indicating an anabolic plateau. Net balance was maximized at ~ 0.15, 0.12, 0.12, and 0.11 g protein·kg- 1·h- 1 in M, F, AM, and AF, respectively. When collapsed across age, the y-intercept (net balance at very low protein intake) was greater (overlapping CI did not contain zero) in adolescents vs. adults. Urea/creatinine excretion increased linearly (all, r ≥ 0.76; P < 0.01) across the range of protein intakes. At plateau, net balance was greater (P < 0.05) in AM vs. M. CONCLUSIONS: Our data suggest there is a practical limit to the anabolic response to protein ingestion within a mixed meal and that higher intakes lead to deamination and oxidation of excess amino acids. Consistent with a need to support lean mass growth, adolescents appear to have greater anabolic sensitivity and a greater capacity to assimilate dietary amino acids than adults.

Nutritionally non-essential amino acids are dispensable for whole-body protein synthesis after exercise in endurance athletes with an adequate essential amino acid intake.

The increased protein requirement of endurance athletes may be related to the need to replace exercise-induced oxidative losses, especially of the branched-chain amino acids (BCAA). However, it is unknown if non-essential amino acids (NEAA) influence the requirement for essential amino acids (EAA) during post-exercise recovery. Seven endurance-trained males ran 20 km prior to consuming [13C]phenylalanine, sufficient energy, and: (1) deficient protein (BASE); (2) BASE supplemented with sufficient BCAA (BCAAsup); (3) an equivalent EAA intake as BCAA (LowEAA), and; (4) sufficient EAA intake (HighEAA). [13C]Phenylalanine oxidation (the reciprocal of protein synthesis) for BCAAsup and HighEAA (0.54 ± 0.15, 0.49 ± 0.11 µmol kg-1 h-1; Mean ± SD) were significantly lower than BASE (0.74 ± 0.14 µmol kg-1 h-1; P < 0.01 for both) and LowEAA (0.70 ± 0.11 µmol kg-1 h-1; P < 0.05 and 0.01, respectively). Our results suggest that exogenous NEAA are dispensable for whole-body protein synthesis during recovery from endurance exercise provided sufficient EAA are consumed. Endurance athletes who may be at risk of not meeting their elevated protein requirements should prioritize the intake of EAA-enriched foods and/or supplements.

Protein Intake at Breakfast Promotes a Positive Whole-Body Protein Balance in a Dose-Response Manner in Healthy Children: A Randomized Trial.

Background: Protein ingestion promotes whole-body net protein balance (NB) in children, which is a prerequisite for growth. Determining how much protein is required at breakfast to promote a positive NB, which may be negative after the traditional overnight fast in children, has yet to be determined. Objective: We determined the impact of incremental doses of milk protein at breakfast as well as the impact of daily dietary protein distribution on NB in children. Methods: A total of 28 children [14 boys, 14 girls; age range: 7-11 y; body mass index (mean ± SD, in kg/m2): 16.0 ± 1.9] completed 2 intervention trials. During the breakfast meal, participants consumed an isoenergetic beverage with different amounts of protein (0, 7, 14, or 21 g for Groups A-D, respectively) and [15N]-glycine to measure whole body protein metabolism. Whole-body nitrogen turnover, protein synthesis (PS), protein breakdown, and NB were measured over 9 and 24 h. Results: Following an overnight fast, children were in negative NB (-64.5 mg · kg-1 · h-1). Protein ingestion at breakfast induced a stepwise increase in NB over 9 h [Groups A (6.2 mg · kg-1 · h-1) < B (27.9 mg · kg-1 · h-1) < C (46.9 mg · kg-1 · h-1) < D (66.0 mg · kg-1 · h-1)] with all conditions different from each other (all P < 0.01). PS was 42% greater in Group D than in Group A over 9 h (P < 0.05). Conclusions: Consuming ≥7 g of the total daily protein intake at breakfast attenuates the observed overnight protein losses in children during the subsequent 9 h following breakfast consumption. The dose-dependent increase in NB over a daytime fed period, inclusive of breakfast and lunch, highlights the importance of breakfast protein intake on acute anabolism in healthy active children. This trial was registered at clinicaltrials.gov as NCT02465151.

Timing and pattern of postexercise protein ingestion affects whole-body protein balance in healthy children: a randomized trial.

The dose and timing of postexercise protein ingestion can influence whole-body protein balance (WBPB) in adults, although comparable data from children are scarce. This study investigated how protein intake (both amount and distribution) postexercise can affect WBPB in physically active children. Thirty-five children (26 males; 9-13 years old) underwent a 5-day adaptation diet, maintaining a protein intake of 0.95 g·kg-1·day-1. Participants consumed [15N]glycine (2 mg·kg-1) before performing 3 × 20 min of variable-intensity cycling, and whole-body protein kinetics were assessed over 6 and 24 h of recovery. Fifteen grams of protein was distributed across 2 isoenergetic carbohydrate-containing beverages (15 and 240 min postexercise) containing reciprocal amounts of protein (i.e., 0 + 15 g, 5 + 10 g, 10 + 5 g, and 15 + 0 g for Groups A-D, respectively). Over the 6 h that included the exercise bout and consumption of the first beverage at 15 min postexercise, WBPB (i.e., synthesis - breakdown) demonstrated a linear increase of 0.647 g·kg-1·day-1 per 1 g protein intake (P < 0.001). Over 24 h, robust regression revealed that WBPB was best modeled by a parabola (P < 0.05), suggesting that a maximum in WBPB was achieved between groups B and C. In conclusion, despite a dose response early in recovery, a periodized protein intake with multiple smaller doses after physical activity may be more beneficial than a single bolus dose in promoting daily WBPB in healthy active children.

Postexercise Dietary Protein Ingestion Increases Whole-Body Leucine Balance in a Dose-Dependent Manner in Healthy Children.

Background: Protein ingestion is important in enhancing whole-body protein balance in children. The effect of discrete bolus protein ingestion on acute postexercise recovery has yet to be determined.Objective: This study determined the effect of increasing doses of ingested protein on postexercise whole-body leucine balance in healthy, active children.Methods: Thirty-five children (26 boys, 9 girls; age range: 9-13 y; weight mean ± SD: 44.9 ± 10.6 kg) underwent a 5-d adaptation diet (0.95 g protein ⋅ kg-1 ⋅ d-1) before performing 20 min of cycling 3 times with a concurrent, primed, constant infusion of [13C]leucine. After exercise, participants consumed an isoenergetic beverage (140 kcal) containing variable amounts of bovine skim-milk protein and carbohydrates (sucrose) (0, 5, 10, and 15 g protein made up with 35, 30, 25, and 20 g carbohydrates, respectively). Blood and breath samples were taken over the 3 h of recovery to determine non-steady state whole-body leucine oxidation (LeuOX) and net leucine balance (LeuBAL).Results: LeuOX (secondary outcome) peaked 60 min after beverage ingestion and demonstrated a relative dose-response over the 3 h of recovery (15 g = 10 > 5 > 0 g; P < 0.001). LeuBAL (primary outcome) demonstrated a dose-response over the 3 h [15 g (24.2 ± 8.2 mg/kg) > 10 g (11.6 ± 4.3 mg/kg) > 5 g (5.7 ± 1.9 mg/kg) > 0 g (-3.0 ± 1.7 mg/kg); all P < 0.01] with all conditions different from zero (all P < 0.001).Conclusions: Over the 3-h postexercise period, LeuBAL was negative with carbohydrate ingestion alone; however, the co-ingestion of carbohydrates and 5 g high-quality dietary protein was sufficient to promote a positive postexercise whole-body protein balance in healthy, active children. Moreover, LeuBAL increased in a dose-dependent manner within the protein range studied. Children should consider consuming a source of dietary protein after physical activity to enhance whole-body anabolism. This trial was registered at clinicaltrials.gov as NCT01598935.

Protein Needs of Physically Active Children.

Current Dietary Reference Intakes (DRI) for protein for children and youth require revision as they were derived primarily on nitrogen balance data in young children or extrapolated from adult values; did not account for the possible influence of above average physical activity; and did not set an upper tolerable level of intake. Revision of the protein DRIs requires new research that investigates: 1) long-term dose-response to identify protein and essential amino acid requirements of both sexes at various pubertal stages and under differing conditions of physical activity; 2) the acute protein needs (quantity and timing) following a single bout of exercise; 3) the potential adverse effects of chronic high intakes of protein; and 4) new measurement techniques (i.e., IAAO or stable isotope methodologies) to improve accuracy of protein needs. While active individuals may require protein in excess of current DRIs, most active Canadian children and youth have habitual protein intakes that exceed current recommendations.

The Effect of Postexercise Milk Protein Intake on Rehydration of Children.

PURPOSE: In adults, rehydration after exercise in the heat can be enhanced with a protein-containing beverage; however, whether this applies to children remains unknown. This study examined the effect of milk protein intake on postexercise rehydration in children. METHOD: Fifteen children (10-12 years) performed three exercise trials in the heat (34.4 ± 0.2 °C, 47.9 ± 1.1% relative humidity). In a randomized, counterbalanced crossover design, participants consumed iso-caloric and electrolyte-matched beverages containing 0 g (CONT), 0.76 g (Lo-PRO) or 1.5 g (Hi-PRO) of milk protein/100 mL in a volume equal to 150% of their body mass (BM) loss during exercise. BM was then assessed over 4 h of recovery. RESULTS: Fluid balance demonstrated a significant condition × time interaction (p = .012) throughout recovery; Hi-PRO was less negative than CONT at 2 hr (p = .01) and tended to be less negative at 3 h (p = .07). Compared with CONT, beverage retention was enhanced by Hi-PRO at 2 h (p < .05). CONCLUSION: A postexercise beverage containing milk protein can favorably affect fluid retention in children. Further research is needed to determine the optimal volume and composition of a rehydration beverage for complete restoration of fluid balance.

Exertion Testing in Youth with Mild Traumatic Brain Injury/Concussion.

PURPOSE: The decision regarding return to activity (RTA) after mild traumatic brain injuries/concussion is one of the most difficult and controversial areas in concussion management, particularly for youth. This study investigated how youth with postconcussion syndrome (PCS) are affected by exertion and whether standardized exertion testing using the McMaster All-Out Progressive Continuous Cycling Test can contribute to clinical decision making for safe RTA. METHODS: Fifty-four youth (8.5-18.3 yr) with a previously confirmed concussion participated in the study. Each participant performed exertion testing on a cycle ergometer and completed a Postconcussion Symptom scale at the following time points: before exertion (baseline), 5 and 30 min, and 24 h after exertion. A modified Postconcussion Symptom scale was administered at 2-min intervals during exertion. RESULTS: Participants had a mean ± SD symptom duration of 6.3 ± 6.9 months after the most recent concussive injury, with a median of 4.1 months (range, 0.7-35 months). Sixty-three percent of participants had symptoms during exertion testing. Symptom profile (number and severity) significantly affected perception of exertion at 50% peak mechanical power. During acute assessment of symptoms (30-min after exertion), headache (P = 0.39), nausea (P = 0.63), and dizziness (P = 0.35) did not change. However, both the number and severity of symptoms significantly improved over 24 h, with 56.8% of youth showing improvements. The time from the most recent injury had a significant effect on the symptom score at baseline, 30 min after exertion, and 24 h after exertion. CONCLUSIONS: Exertion testing has an important role in the evaluation of symptoms and readiness to RTA, particularly in youth who are slow to recover. Overall, controlled exertion seemed to lesson symptoms for most youth.

Postexercise protein ingestion increases whole body net protein balance in healthy children.

Postexercise protein ingestion increases whole body and muscle protein anabolism in adults. No study has specifically investigated the combined effects of exercise and protein ingestion on protein metabolism in healthy, physically active children. Under 24-h dietary control, 13 (seven males, six females) active children (∼ 11 yr old; 39.3 ± 5.9 kg) consumed an oral dose of [(15)N]glycine prior to performing a bout of exercise. Immediately after exercise, participants consumed isoenergetic mixed macronutrient beverages containing a variable amount of protein [0, 0.75, and 1.5 g/100 ml for control (CON), low protein (LP), and high protein (HP), respectively] according to fluid losses. Whole body nitrogen turnover (Q), protein synthesis (S), protein breakdown (B), and protein balance (WBPB) were measured throughout exercise and the early acute recovery period (9 h combined) as well as over 24 h. Postexercise protein intake from the beverage was ∼ 0.18 and ∼ 0.32 g/kg body mass for LP and HP, respectively. Q, S, and B were significantly greater (main effect time, all P < 0.001) over 9 h compared with 24 h with no differences between conditions. WBPB was also greater over 9 h compared with 24 h in all conditions (main effect time, P < 0.001). Over 9 h, WBPB was greater in HP (P < 0.05) than LP and CON with a trend (P = 0.075) toward LP being greater than CON. WBPB was positive over 9 h for all conditions but only over 24 h for HP. Postexercise protein ingestion acutely increases net protein balance in healthy children early in recovery in a dose-dependent manner with larger protein intakes (∼ 0.32 g/kg) required to sustain a net anabolic environment over an entire 24 h period.

Effects of postexercise milk consumption on whole body protein balance in youth.

In adults, adding protein to a postexercise beverage increases muscle protein turnover and replenishes amino acid stores. Recent focus has shifted toward the use of bovine-based milk and milk products as potential postexercise beverages; however, little is known about how this research translates to the pediatric population. Twenty-eight (15 girls) pre- to early pubertal (PEP, 7-11 yr) and mid- to late-pubertal (MLP, 14-17 yr) children consumed an oral dose of [(15)N]glycine prior to performing 2 × 20-min cycling bouts at 60% V̇O(2 peak) in a warm environment (34.5°C, 47.3% relative humidity). Following exercise, participants consumed either water (W), a carbohydrate-electrolyte solution (CES), or skim milk (SM) in a randomized, cross-over fashion in a volume equal to 100% of their body mass loss during exercise. Whole body nitrogen turnover (Q), protein synthesis (S), protein breakdown (B), and whole body protein balance (WBPB) were measured over 16 h. Protein intake from SM was 0.40 ± 0.10 g/kg. Over 16 h, Q and S were significantly greater (P < 0.01) with SM than W and CES. B demonstrated a trend for a main effect for beverage (P = 0.063). WBPB was more negative (P < 0.01) with W and CES than with SM. In the SM trial, WBPB was positive in PEP, although it remained negative in MLP. Boys exhibited significantly more negative WBPB than girls (P < 0.05). Postexercise milk consumption enhances WBPB compared with W and CES; however, additional protein intake may be required to sustain a net anabolic environment over 16 h.

Effect of milk consumption on rehydration in youth following exercise in the heat.

Low-fat milk is thought to be an effective postexercise rehydration beverage in adults; however, little is known about milk's rehydration ability in children after exercising in the heat. This study tested the hypothesis that because of its electrolyte and protein content, skim milk (SM) would be more effective than both water (W) and a carbohydrate/electrolyte solution (CES) in replacing body fluid losses in children following exercise in the heat. Thirty-eight (19 females) heat-acclimated pre- to early pubertal (PEP, aged 7-11 years) and mid- to late-pubertal (MLP, aged 14-17 years) children performed 3 sessions in 34.5 °C, 47.3% relative humidity, consisting of 2 × 20-min cycling bouts at 60% peak oxygen uptake followed by consumption of either W, CES, or SM. Each beverage was consumed immediately after exercise in a volume equal to 100% of their body mass loss during exercise. Urine samples were collected before, during, and after exercise, as well as the 2-h period following beverage consumption. On average, children dehydrated 1.3% ± 0.4%. Children ingested 0.40 ± 0.11 L (PEP) and 0.74 ± 0.20 L (MLP) of fluid. The fraction of the ingested beverage retained at 2 h of recovery was greater with SM (74% ± 18%) than W (47% ± 26%) and CES (59% ± 20%, p < 0.001 for both), and greater in CES than W (p < 0.001). All participants were in a hypohydrated state after 2 h of recovery, following the pattern SM < CES < W. In both PEP and MLP children, SM is more effective than W and CES at replacing fluid losses that occur during exercise in the heat.