Changes in Blood Electrolytes and Plasma Volume in National Football League Players During Preseason Training Camp

Abstract

Blood samples were drawn from 6 National Football League players for baseline measures and then prior to morning practice on days 3, 5, and 9. Mean blood sodium level was lower on days 3 (136.9±0.6 mmol·L -1 ) and day 5 (138.1±0.6 mmol·L -1 ) compared to baseline (140.4±0.4 mmol·L -1 ) and day 9 (140.3±0.4 mmol·L -1 ). Mean blood potassium level was higher on day 5 (4.16±0.13 mmol·L -1 ) and day 9 (4.36±0.08 mmol·L -1 ) compared to baseline (3.77±0.15 mmol·L -1 ). Mean plasma volume was lower on day 3 (-4.9%±2.4%) compared to day 5 (4.5%±1.9%), and mean mass (days 2 through 9) was below baseline before and after practices. Blood sodium level declined by day 3 of preseason and was maintained at low normal levels at the expense of contracted plasma volume. Increased resting blood potassium levels on days 5 and 9 indicated rhabdomyolysis. Increased consumption of sodium is important for professional football players to maintain plasma volume during the first week of preseason.