Pre-exercise sodium loading raises plasma volume and extends running time in the heat
Participants
n=8 endurance-trained male runners (VO2max 58 ± 5 ml/kg/min, age 36 ± 11 yr)
Protocol
High-sodium beverage (164 mmol Na+/L) vs low-sodium (10 mmol Na+/L), 10 mL/kg (~757 mL), drunk in seven portions over 60 min starting 105 min before exercise
Run to exhaustion at 70% VO2max in warm conditions (32°C, 50% RH, airflow ~1.5 m/s); trials 1-3 weeks apart
Sodium dose: 164 mmol/L × ~0.757 L ≈ 124 mmol ≈ 2.9 g sodium (arithmetic on the abstract's figures)
Key Results
Plasma volume before exercise: +4.5 ± 3.7% with high sodium vs 0.0 ± 0.5% with low sodium (p=0.04)
Time to exercise termination: longer with high sodium — 57.9 vs 46.4 min in the six runners stopped at the ethical core-temperature end point (39.5°C; p=0.04), and 96.1 vs 75.3 min in those who ran to exhaustion (p=0.03)
At matched time before termination: lower core temperature (38.9 vs 39.3°C, p=0.00), lower perceived exertion (p=0.01), tendency to lower heart rate (164 vs 174 bpm, p=0.08)
Practical Application
Finding: in 8 endurance-trained runners, ~757 mL of a 164 mmol/L sodium drink (≈2.9 g sodium) taken over the hour ending 45 min before a run at 70% VO2max in 32°C raised plasma volume by 4.5% and extended time to exhaustion (96 vs 75 min), with lower core temperature and RPE. Sodium pre-loading is a legitimate heat-race tool for a hot start.
Timing as tested: drink finished ~45 min before the start (portions from 105 to 45 min pre-exercise), not a single bolus.
Not from this paper; the base's own practice: combine with pre-cooling and the usual carbohydrate pre-load; check tolerance in training first — a concentrated sodium drink can cause GI upset.
Limitations
n=8, men only, one run-to-exhaustion model in 32°C; a fixed-distance race or cycling were not tested
Six runners were stopped at the ethical core-temperature cut-off (39.5°C) rather than at exhaustion — the exhaustion-time comparison rests on the few who ran to exhaustion
How this entry was checked and changed
Why this level
regraded 2026-09-27 from B+: crossover, n=8
Content correction 2026-09-27
"1.7 g Na 3 h before exercise" -> abstract: 164 mmol/L beverage, 10 mL/kg (~757 mL ≈ 124 mmol ≈ 2.9 g sodium), drunk over 60 min starting 105 min before exercise. Dose and timing corrected.
"Delays dehydration" -> not in the abstract; replaced by the measured outcomes (plasma volume +4.5%, longer time to termination, lower core temperature, RPE, HR trend).
Sport "general" -> running (trained runners, running to exhaustion); type "Research" -> double-blind crossover; level B+ -> B (crossover, n=8).