Water Loading in Combat Sport Athletes as a Means to Acutely Manipulate Body Mass

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Athletes in weight category sports practice various methods of acute weight loss, with recent research and long standing “grey literature” demonstrating the popularity of ‘water loading’ (the consumption of large volumes of fluid for several days, prior to withholding intake) as a means to increase body water losses following fluid restriction. No research has examined this technique or its risk of causing hyponatremia. PURPOSE: To determine the effectiveness and safety of water loading and assess potential mechanisms. METHODS: Male combat sport athletes (n=21, 77.5±8.1kg 177.5±6.1cm, 26.6±4.0years) were separated into a control (CON, n=10) and water loading (WL, n=11) group. Subjects were fed a standardised isoenergetic diet based on fat free mass (assessed via DXA scan) controlling for macronutrient, sodium and fibre content for 6 days. Day 1-3 fluid intake was 40mL/kg CON and 100mL/kg WL. Day 4 fluid intake was 15mL/kg CON and WL. Day 5 no fluid was consumed until midday with both groups following the same rehydration protocol until day 6. Urine sodium, specific gravity (USG) and volume were recorded alongside training sweat losses and sleep quality/ duration (measured via actigraphy) throughout. Renal hormones (vasopressin, renin, and aldosterone), blood urea and electrolytes (U+Es) and body mass (BM) were measured each morning (fasted) and evening following 30 min supine rest. Physical performance was assessed pre and post intervention. Two way repeated measures ANOVAs were used to assess differences between groups. RESULTS: Following fluid restriction, significant differences with large effect sizes were found in fluid input/output ratio (39.11%, p < 0.01, ES=1.2) and BM loss (0.6%BM, p=0.02, ES=0.82). No differences in sleep or performance measures existed. Time had a significant effect on USG, all U+Es and renal hormones (p < 0.05). An interaction effect existed between time and intervention on blood sodium, potassium, chloride, urea, creatinine, USG and vasopressin (p < 0.05) but not on other hormones or electrolytes. No mean U+Es differed from reference range or approached critical values. CONCLUSION: Water loading appears to be a safe and effective method of acute BM loss under the conditions utilised in this study. Changes in vasopressin may in part underlie the mechanism facilitating this technique.