Context: Sodium (Na+) depletion decreases performance and is a primary contributor to hypohydration, exercise associated muscle cramps and hyponatremia. The National Athletic Trainer's Association recommends adding 0.3 – 0.7 g/L Na+ to fluids ingested 2-3 hours prior to exercise to help prevent the negative effects of Na + depletion, but the optimum time of ingestion prior to exercise and amount of Na+ needed to significantly raise plasma Na + concentration (P[Na+]) has yet to be determined. Objective: To determine changes in P[Na+] and urine Na+ concentration (U[Na+] ) and the hydration measures of urine specific gravity (USG ), urine color (Ucol), and percent change in body mass (%ΔBM) over a period of 3 hours of rest following ingestion of 3 different beverages of varying Na+ concentration ([Na+]). Design: Randomized crossover design to examine the effects of the ingestion of water (W), carbohydrate electrolyte beverage (CEB), and enhanced carbohydrate electrolyte beverage (E-CEB) on P[Na+], U[Na +] and hydration measures over a period of 3 hours of rest. Setting: Laboratory in the Department of Physical Education and Athletic Training. Participants: Ten moderately trained (training 3 d/wk for ≥ 90 min total), healthy volunteers from the University of South Carolina and surrounding community. Main Outcome Measures: P[Na +], U[Na+], USG , Ucol, and %ΔBM. Results: Participants were 10 (4 male and 6 female; mean age = 22 ± 2.49 years, weight = 64.3 ± 11.5 kg, height = 171.45 ± 8.9 cm) moderately active individuals from the surrounding area. Mean [Na+] for W = 0 g/L, CEB = 5.1 g/L, and E-CEB = 12.5 g/L. Repeated measures ANOVA and Spearman rho correlations were used to calculate changes and assess relationships between [PNa+], [UNa+], U% SG, Ucol, and %ΔBM. We found a significant increase in overall [PNa+] over the 3 hours (135.0 ± 2.4 mmol/L to 137.2 ± 1.9 mmol/L, p = 0.0001). Mean P[Na +] was significantly lower at 30 min (134.1 ± 2.4 mmol/L) compared to all subsequent time points (p < 0.004). No significant differences were found between the 3 beverage groups for [PNa+] across time. There was a significant increase in overall [UNa +] from 0 to 180 min (5.2 ± 1.0 mmol/L to 12.3 ± 2.0 mmol/L, p = 0.002). At min 180, E-CEB (20.5 ± 11.6 mmol/l) was significantly higher than W (5.5 ± 2.9 mmol/l, p = 0.015). At min 120 E-CEB (12.8 ± 8.7 mmol/l) was significantly greater than both W (4.2 ± 2.4 mmol/l, p = 0.02) and CEB (5.1 ± 5.7 mmol/l, p = 0.04) Mean Ucol decreased significantly from 0 to 60 min (2.8 to 1.7, p < 0.001) then significantly increased to min 120 (2.2, p < .021) and 180 (3.0, p = .000). P[Na+] was significantly correlated with U[Na+] (.424, p=.000), USG (.313 p < .001) and Ucol (.304, p<.001). USG and Ucol were significantly correlated with U [Na+] at the p=.000 level (.504 and .428, respectively) and to each other (.883, p=.000). Change in %ΔBM was significantly correlated with both USG (-.256, p<.004) and Ucol (-.338, p<.001). <p> Conclusions: Overall, the results of our study in combination with previous research may offer some implications for the clinical setting. First, athletes, whether they are sodium depleted or not, need longer than three hours to raise Na+ levels following exercise or inadequate dietary intake. Additional research is necessary to determine an adequate amount of time. Secondly, ingestion of an E-CEB prevents a rapid drop in P [Na+] following fluid ingestion. If this also occurs during exercise, it could lead to a smaller Na+ deficit. Future research needs to examine the changes in P[Na+] during exercise following the ingestion of beverages of varying [Na +]. Future studies should also consider measuring plasma hormone levels and revisiting current fluid recommendations in regards to additional sodium ingestion.
Key Words: dehydration, electrolyte depletion, hyponatremia, urine specific gravity, urine color, body mass
|Commitee:||Davis, Mark, Dompier, Tom|
|School:||University of South Carolina|
|School Location:||United States -- South Carolina|
|Source:||MAI 50/06M, Masters Abstracts International|
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