Working Theory 02

You've heard it from every direction: take salt tabs the week before your race, drink electrolytes all day, load sodium for days leading into competition. The messaging from supplement brands, fellow athletes, and social media has gotten louder — and more confusing. So what does the research actually say?

A comprehensive 2025 review in Sports Medicine for Open (McCubbin) examined every rationale athletes commonly use for sodium supplementation — daily, before, during, and after exercise — and the conclusion is clear: most of what you've been told is either incomplete or not supported by evidence. Sodium matters, but only in relation to how much water you drink with it.

Sodium loading is the deliberate intake of sodium — usually as sodium chloride (table salt) — in a specific concentration alongside fluid in the 60–120 minutes before exercise. The goal is hyperhydration: temporarily raising total body water above your normal baseline so you begin the race with a larger fluid reserve.

This is fundamentally different from the increasingly popular practice of adding sodium to every glass of water you drink throughout the day, or taking salt capsules for several days before race day. The research shows that multi-day sodium loading is largely ineffective because the kidneys excrete the excess within hours. In one controlled study, athletes who doubled their sodium intake for three days retained only about 21% of the extra sodium. By contrast, a single acute dose of 75 mg/kg consumed within four hours of exercise retained approximately 77% of the ingested sodium.

Three recent studies form the foundation of this Working Theory:

Study 1 — The Review (McCubbin, 2025). Published in Sports Medicine for Open, this review examined evidence for sodium supplementation at every time point: daily intake, pre-exercise, during exercise, and post-exercise. The central finding is that there is no evidence athletes require greater daily sodium intake than the general population. Most athletes already consume well above recommended levels (3,100–3,900 mg/day) simply through normal eating. When sodium loading is beneficial, it is beneficial acutely — consumed 1–4 hours before exercise at a concentration of 275–420 mg sodium per 100 mL of fluid. NaCl in solution was slightly more effective than capsules for fluid retention.

Study 2 — Female Cyclists in the Heat (Jardine et al., IJSNEM, 2025). Twelve endurance-trained female cyclists consumed 30 mL/kg fat-free mass of fluid containing 7.5 g/L NaCl before cycling at 60% VO₂peak in 34°C heat, then completed a 200 kJ time trial. The results:

Time-trial completion was 1.55 minutes faster with sodium (22.4 min vs. 24.0 min; p = 0.001). Average power output increased by 10 watts. Critically, these improvements came with no change in core temperature or heart rate — meaning athletes worked harder without greater thermal or cardiovascular strain.

Study 3 — Hydration Responses Across Menstrual Phases (Jardine et al., Nutrients, 2025). A companion study on the same cohort measured hydration responses at rest and found sodium hyperhydration increased fluid retention by 509 mL, reduced urine output by 107 mL, and lowered body-mass loss during exercise by 0.20%. During the early-follicular phase, the effect was even stronger: body-mass loss was reduced by 0.26%, and vasopressin (the hormone that signals dehydration) dropped by 10.8 pg/mL.

Daily sodium supplements "because you're an athlete." There is no evidence that athletes need more sodium day-to-day than non-athletes. Sodium intake is positively correlated with energy intake — as your training volume increases, you naturally eat more and consume more sodium without trying. The social-media-driven message that "water doesn't hydrate you" is, per the review, "an overly literal interpretation of the failure to retain large, excessive quantities of plain water when consumed rapidly in large boluses." When you eat food alongside water — as you do at every meal — fluid retention is equivalent to sodium-enhanced beverages.

Multi-day sodium loading. The kidneys adjust natriuresis (sodium excretion) within as little as two hours of oral intake and increase output significantly by eight hours. Three days of doubled sodium intake yielded only ~21% retention. A single pre-race dose retained 77%. Save your money and your kidneys.

Matching sweat sodium losses milligram-for-milligram during exercise. Sweat sodium concentration is highly individual and changes with heat acclimation, hydration status, and dietary sodium intake. The review is clear: sodium intake during exercise should be planned relative to fluid balance, not as an isolated replacement of sweat losses. Consuming sodium without adequate fluid, or too much fluid without adequate sodium, creates the mismatch that leads to GI distress, bloating, or exercise-associated hyponatraemia (EAH).

Nathan Martin — 2026 LA Marathon, 2:11:17 (Champion). Martin, 36, won the Los Angeles Marathon with a finishing kick for the ages, edging Michael Kamau in a sprint finish. He became the first U.S.-born Black man to win the event. His individualized hydration protocol: 832 mL of fluid per hour with a relative sodium concentration of 1,283 mg/L (~128 mg per 100 mL). This falls within the evidence-based range, and the plan was developed using sweat testing and practiced across multiple long runs before race day.

The lesson isn't to copy Martin's exact numbers — it's that he treated sodium and water as a unified system, tested it repeatedly, and executed it on race day without improvisation.

You'll notice these signs if the protocol is effective: You urinate 1–2 times in the 60 minutes after finishing your pre-race drink, and the urine is pale but not totally clear. You feel hydrated but not bloated. Your body weight is 0.5–1.0 kg above your normal morning weight. During the race, you maintain your target pace without early-onset thirst or GI cramping. Post-race, you haven't lost more than 2–3% of your starting body mass.

If something goes wrong: Nausea or stomach sloshing means you've either consumed too much volume or the sodium concentration was too high. Excessive urination (3+ trips) with clear urine means the concentration was too low. Adjust the ratio, not just the total amount.

Rule 1 — Always think sodium + water, never sodium alone. Every problem — GI distress, EAH, cramping, bloating — traces back to a mismatch between these two. Sodium capsules without water are a mismatch. Chugging plain water without sodium is a mismatch. Every time you plan sodium, plan the fluid that goes with it.

Rule 2 — Acute beats chronic. One well-timed dose 90 minutes before your race retains more fluid than a week of salty meals. Save multi-day loading for the marketing brochures.

Rule 3 — Practice in training. Your first time using a hyperhydration protocol should never be race morning. Test it before your next long run or hard session in conditions similar to race day. Note GI response, urination pattern, and how you feel at the 60-minute mark.

Rule 4 — Hotter conditions amplify the benefit. The performance advantage of sodium hyperhydration is most pronounced in heat (>30°C / 86°F). If you're racing in cool conditions with moderate effort, the benefit is smaller and may not justify the GI risk.

Rule 5 — Women: factor in your cycle. If you race in the luteal phase, sodium hyperhydration may counteract progesterone-driven fluid loss and elevated core temperature. The data shows the benefit is stronger in Phase 4 than Phase 1.

The optimal sodium dose for athletes of different sizes, sweat rates, and fitness levels hasn't been personalized in a large-scale trial. Most hyperhydration studies use laboratory cycling protocols — direct data on running, triathlon swim starts, and ultra-distance events is limited. We also lack clear evidence on whether sodium form (NaCl vs. sodium citrate vs. sodium bicarbonate) produces meaningfully different outcomes for performance beyond fluid retention. The interaction between sodium hyperhydration and carbohydrate loading — two protocols athletes often combine on the same morning — remains unstudied.