Dear editor: Sport beverages contain electrolytes and carbohydrates, rather than just water, and are recommended to maintain hydration during high endurance exercise at high ambient temperatures.¹ However, the benefit of sport beverages over water alone for short-term, high intensity exercise, after dehydration, has not been consistently demonstrated. Knowledge of the most effective fluid supplementation to improve exercise performance would be particularly important for athletes who use ‘forced’ dehydration in a sauna to achieve rapid weight-loss prior to competition, such as in wrestling and mixed-martial-arts.² The purpose of our study was to compare the effects of mineral water to a sport beverage for fluid replenishment after forced dehydration on lactate levels at rest and after high intensity treadmill exercise.

Participants were seven male university students, with an unremarkable medical history, and the following relevant characteristics: mean age, 24.57±2.15 years; mean height, 172.27±8.39 cm; mean weight, 67.57±7.58 kg; and mean VO2max, 51.07±13.12 ml/kg/min. The dehydration protocol was standardized to induce a 3% decrease in body weight through fluid loss.³ Fluid supplementation was provided within 2 h of dehydration using two types of supplements, mineral water and a sport beverage containing 6% carbohydrate, 20.9 mEq/L Na+, 6.1 mEq/L K+, and 9.5 mEq/L Cl−. The graded treadmill exercise test to exhaustion (GXT; intensity of 80% VO₂max) was used for exercise testing. Blood samples for measurement of lactate levels were obtained at baseline (prior to the exercise), at the 15 min time point of exercise, immediately upon cessation of exercise, and at 60 min post-exercise. The GXT was completed under four conditions: control (no prior dehydration), dehydration, dehydration followed by fluid supplementation with mineral water, and dehydration followed by fluid supplementation with the sport beverage. Plasma lactate levels were measured using a clinical chemistry analyzer (Ektachem DT 60; Eastman Kodak, Rochester, NY, USA).

Differences in lactate levels at each time point of measurement were evaluated using a two-way repeated analysis of variance (ANOVA; SPSS Inc., Chicago, IL, USA; p<0.05). Lactate levels for the four conditions, at each time point of measurement, are reported in table I. A significant main effect of time and group on plasma lactate levels was identified, as well as a significant time by group interaction. Post-hoc analysis revealed a continuous increase in lactate levels, from baseline, through to immediately upon cessation of exercise, followed by a significant decrease at 60 min post-exercise for all groups. Lactate levels at the cessation of exercise were significantly higher for the dehydration than the control condition (p<0.05).

Table I Change in lactate level by exercise according to fluid replenishment method after dehydration 

Data are presented as mean ± standard deviation (Unit: mmol/l)

^* Significantly different from rest in all trials (p<0.05)

^‡ Significantly higher in dehydration than control trial (p<0.05)

Dehydration prior to exercise accelerates the production of lactate, and both mineral water and a sport beverage are effective in reducing the levels of lactate produced.