Fluid balance in young swimmers: could the different color of drinking bottles change water intake during swimming practice?

BACKGROUND: The possibility of using colors of drinking bottles to manage fluid intake is an attractive idea. We describe the water intake and fluid balance of young swimmers and to test if their water intake changes when they use white drinking bottles compared to standard transparent drinking bottles. METHODS: A cross-over study with repeated-measures was carried out. A group of 25 adolescent competitive swimmers participated in the study. We recorded the fluid balance of three practice sessions with white drinking bottles and we recorded the fluid balance of two practice sessions with transparent drinking bottles. RESULTS: The swimmers started their afternoon practice close to the euhydration threshold. Body water loss from swimming practice seems to be easily replaced through the water intake. The water intake (2.4 mL/min), the sweat rate (2.64 g/min) and the percentage of net fluid balance (-0.2%) were low. Based on urine specific gravity analysis, the urine samples after the practice showed a dilution of the urine (P=0.042). Urine color analysis showed the dilution of the urine with a paler color after practice (P=0.031). A significant higher water intake with white drinking bottles than with transparent drinking ones was recorded (white versus transparent drinking bottles: 3.1±2.2 vs. 1.9±1.7 mL/min; P=0.008; medium effect size 0.60). CONCLUSIONS: The present study suggests that water should be considered a reliable source of liquid in swimming. The white color of the drinking bottles could act at a non-conscious level and increase the water intake of the swimmers. The color of the drinking bottle could be an effective strategy for optimizing hydration