Effectiveness of revised fluid replacement guidelines for military training in hot weather

BACKGROUND: This study compared the revised U.S. Army fluid replacement guidelines (REV) with the old guidelines (OLD) on daily changes in serum sodium concentration (Na+) and body mass (BM) during Basic Combat Training at Fort Benning, GA during two successive summers. METHODS: Recruits (n = 550; OLD = 277, REV = 273) were evaluated before and after 8-12 h of outdoor military combat training in hot weather. The WBGT (mean +/- SD) averaged 26.6 +/- 1.7 degrees C for OLD and 27.4 +/- 0.9 degrees C for REV (NS). RESULTS: Serum Na+ decreased from 137.5 +/- 1.6 mEq x L(-1) to 137.0 +/- 2.1 mEq x L(-1) after outdoor military training in OLD (p < 0.05). Twenty-two recruits (8%) had serum sodium fall to below 135 mEq x L(-1) during OLD. Serum Na+ increased from 139.0 +/- 1.7 mEq x L(-1) to 139.4 +/- 2.1 mEq x L(-1) after outdoor military training in REV (p < 0.05). Only two recruits (1%) had serum Na+ fall to below 135 mEq x L(-1) during REV. BM increased an average of 1.3 +/- 1.4 kg (p < 0.05) in OLD and an average of 0.4 +/- 1.7 kg in REV (p < 0.05). CONCLUSIONS: The revised guidelines effectively reversed the decrease in serum sodium, reduced the increase in body mass, maintained hydration and minimized overdrinking during hot weather military training compared with the old fluid replacement guidelines.