The Effect of Sodium Supplementation on Postexercise Hypotension Following Acute Submaximal Aerobic Exercise

Abstract

PURPOSE: Acute submaximal aerobic exercise confers cardiovascular benefits including a prolonged reduction in blood pressure (BP) termed postexercise hypotension (PEH). PEH is thought to contribute to the chronic BP-lowering effects of aerobic training. Chronic sodium (Na+) supplementation expands plasma volume (PV) and may attenuate PEH. Therefore, this study tested the hypothesis that Na+ supplementation attenuates PEH following acute aerobic exercise. METHODS: Healthy young adults (n=11, age 26 ± 4 years; body mass index 23.5 ± 2.4 kg/m2) consumed a recommended Na+ diet (2,300 mg Na+/d) for 10 days on two occasions; participants also consumed pills containing a total of either 4,000 mg Na+ or a placebo in random order. Participants collected their urine for the final 24 hours of each intervention for quantification of urinary Na+ excretion. On day 10 of each intervention, participants completed 50 minutes of dynamic cycling exercise at 60% VO2peak. Brachial BP was recorded via automated oscillometry before and every 10 minutes after exercise for one hour. The change in PV was estimated using hemoglobin and hematocrit following each intervention. BP responses following exercise were compared using a two-way repeated measures ANOVA. Urinary and blood measures and the nadir in BP after exercise were compared using paired t-tests. RESULTS: The mean VO2peak of participants was 41.6 ± 8.8 ml/min/kg and mean power at 60% VO2peak was 127 ± 40 W. Urinary Na+ excretion was increased following Na+ supplementation (277 ± 50 vs. 153 ± 73 mmol/24 hours, p<0.001). Na+ supplementation expanded PV approximately 10.2 ± 8.9%. Despite significantly greater Na+ excretion, serum [Na+] (141.0 ± 1.8 vs. 141.7 ± 3.0 mEq/L, p=0.34) and plasma osmolality (294 ± 4 vs. 295 ± 6 mOsm/kg H2O, p=0.22) were not different following Na+ supplementation compared to placebo. PEH was observed following both conditions (nadir systolic BP: -4.7 ± 3.8 vs. -4.6 ± 2.9 mmHg, p=0.91 and mean BP: -6.1 ± 4.3 vs. -5.0 ± 3.4 mmHg, p=0.38). However, when comparing Na+ supplementation to placebo, there was not a significant diet effect regarding reductions in systolic BP (p=0.93) or mean BP (p=0.41) following exercise. CONCLUSIONS: These preliminary data suggest that Na+ supplementation does not attenuate PEH following acute aerobic exercise despite increased PV.