DIETARY SODIUM INTAKE AND AEROBIC CAPACITY

Abstract

232 The purpose of this study was to determine the changes in maximal and submaximal aerobic capacities of subjects of an average fitness level on a sodium restricted diet (SRD) compared to their baseline diet(BD). Ten healthy males (age: 25±4 yrs, height: 70±3.4 in., weight: 160±25 lbs.) volunteered and were randomly placed on a low sodium diet (≤1500 mg Na) or remained on their typical diet for 5 days and then switched to the opposite diet for 5 days. Maximal treadmill exercise tests were completed on the fifth day of each diet following two 24-hour urine collections, used to determine electrolyte excretion levels. Blood samples were taken on the last day of each diet to measure plasma renin activity (PRA) and hematocrit. Indirect calorimetry was used to analyze oxygen consumption (VO2) and ventilation (VE). Heart rate (HR) and time to exhaustion (TE) were recorded for each exercise test. An ANOVA (p=0.05) established that a significant difference for urinary sodium excretion (mEq/day) was present between the BD(3389±950) and SRD (1174±560). PRA (ng/ml/hr) was significantly different on the BD (0.837±0.549) and SRD (1.608+0.926). Subjects remained weight stable and no significant differences were seen in hematocrit(%) on the BD (45.1+1.8) and SRD (45.7±1.5). No significant differences were noted for maximal VO2 (55.8±6.0, 57.4±7.8 ml/kg BW/min), HR (191±6.1, 190±5.0 bpm), VE (141±21, 124±30 l/min) and TE (14.8±2.8, 14.8±3.2 s) on the BD and SRD, respectively. Submaximal data at 50% and 75% showed no significant differences for VO2, HR, and VE on the BD and SRD. It is concluded from these data that a sodium restricted diet does not lower maximal aerobic capacities or submaximal responses to exercise.