Blood Electrolyte, Plasma Volume And Body Weight Changes In Sodium Supplemented NFL Players During Preseason

Abstract

Preseason training for teams in the National Football League (NFL) consists of consecutive weeks of two-a-day practices during the hottest months of the year. The large body surface area (BSA) of football (FB) players combined with wearing equipment which reduces dry heat dissipation results in high sweat, and therefore substantial sodium (Na+) losses. PURPOSE To Na+ supplement NFL FB players with a history of heat-related illness during the first week of two-a-day s and measure blood electrolytes and changes in plasma volume (PV) and body weight (BW). METHODS Six NFL veterans with mean playing time in the league = 5.3 ± 2.3 yr, (range = 3–8 yr) and age = 25.5 ± 2.6yr, height = 186.3 ± 5.5 cm, weight = 104 ± 17.6 kg and BSA = 2.28 ± 0.19 m2 participated in the study. Blood samples were taken from subjects for baseline (BL) measures upon arrival to camp and prior to the morning (AM) practice on Days 3, 5 and 9. Blood Na+, potassium (K+), calcium (Ca++) and pH were determined by ion-selective electrode and percent change in PV was calculated using hematocrit and hemoglobin. BW was recorded to the nearest 1/2 1b before and after practices. Percent dehydration (%Dehy) was calculated from the change in BW from BL measures. Players did physical testing on Day 1, practiced two times per day on Days 2, 3 and 4, and then alternated one or two practice sessions per day for Days 5 through 9. Players were supplemented at and between meals with oral electrolyte solutions containing higher Na+ concentrations than that of commercial sports drinks. All subjects received a minimum of 4330 mg of Na+ per day above normal dietary intake. Data were analyzed with repeated measures and one-way ANOVA. RESULTS Mean wet bulb globe temperatures for days 1 – 9 were 23.3°C for AM and 26.5°C for afternoon (PM) practices. Blood Na+ was not different on Day 3 (141.1±1.01mmol · l−1) or Day 5 (140.2 ± 0.97 mmol · l−1) compared to BL (141±1.5mmol · l−1) but was lower on Day 9 (138.9 ± 1.6 mmol · l-1) compared to BL and Day 3. No differences were found for blood K+, Ca++ or pH. PV increased 10% by Day 5. Pre and post-practice %Dehy from BL on days 2, 3, 4, 5, and 9 (16 measures including 2 practices on days 2, 3 and 4, and one practice on days 5 and 9) were not different. Pooled data from all days revealed that %Dehy post-AM practice was higher than BL, pre-AM and pre-PM practice, and %Dehy post-PM practice was higher than pre-AM and pre-PM practice, all p<0.01. CONCLUSIONS Blood Na+ levels did not decline during the first 5 days of preseason training in Na+ supplemented NFL players. BW was maintained through day 9. Na+ supplementation is useful in maintaining Na+and fluid balance in professional FB players during the first week of pre-season two-a-day training.