What Electrolytes Do Runners Need?
The cramp that ends a race is obvious. The fluid balance that quietly degrades performance across the final 10 kilometres is not. Most runners who think they bonked, faded, or lost pace in the heat were experiencing electrolyte-related deterioration long before anything felt acutely wrong.
Electrolytes are not a recovery supplement or a hydration luxury. For any runner doing sessions longer than 60–75 minutes — and for almost everyone racing from 10km upward — they're a physiological necessity. The question isn't whether you need them. It's which ones, in what amounts, and when.
"The sports nutrition market treats electrolytes like a marketing category. Most products list four or five minerals and imply the more you take, the more you benefit. The physiology is more specific than that. Sodium does the heavy lifting in endurance running — it drives fluid retention, supports carbohydrate absorption, and is the primary mineral lost in meaningful quantities through sweat. The others have roles, but sodium is where the plan lives or dies."
— Alistair Brownlee, Two-time Olympic Triathlon Champion and founder of truefuels
The four electrolytes runners need — and what each actually does
Sodium: the critical one
Sodium is lost in sweat in the highest concentrations of any mineral. Sweat sodium concentration typically ranges 20–80 mmol/L — equivalent to approximately 1.2–4.6g of salt per litre (NIH sweat composition data; GSSI). The average is around 2.5g salt per litre.
What sodium does during running:
- Maintains plasma volume — prevents blood from thickening as you lose fluid, which keeps cardiovascular efficiency higher
- Drives fluid retention — makes the fluid you drink more effective at staying in the body rather than passing straight through
- Enhances carbohydrate absorption — sodium co-transports glucose through SGLT1 in the intestine, meaning your fuel is absorbed more effectively when sodium is present
- Supports nerve and muscle function — electrical signalling in muscles depends on sodium gradients
Signs of insufficient sodium: feeling bloated from drinking water without improvement, pace fading for no fitness reason, unusual thirst despite adequate fluid intake, visible white salt lines on kit.
Potassium: supporting sodium
Potassium works alongside sodium to regulate fluid balance inside and outside cells. It's also involved in muscle contraction and nerve signal transmission.
Sweat potassium losses are much smaller than sodium losses — approximately 150–200mg per litre of sweat, compared to 1,000–2,500mg of sodium per litre. Most runners lose modest amounts in normal training. Where potassium becomes more relevant is in very long or hot efforts where cumulative losses add up.
The truefuels Performance Gel includes 288mg of natural potassium per serving from coconut — a clean, natural source that avoids the harsh taste that potassium chloride creates in many sports drinks.
Magnesium: muscle and metabolic function
Magnesium supports over 300 enzymatic processes, including energy production, protein synthesis and muscle contraction. Sweat magnesium losses are relatively small (typically 4–7mg per litre), but sustained exercise, heat stress and high-intensity training can create cumulative depletion over time.
Magnesium is not a direct cramp cure, despite common marketing claims. The relationship between magnesium and cramping is more complex — neuromuscular fatigue and training load play larger roles than isolated magnesium deficit in most athletes. What it does support is recovery, sleep quality and sustained muscle function across a training block.
Chloride: sodium's counterpart
Chloride pairs with sodium in sweat — the two are lost together as sodium chloride (salt). Its role is maintaining fluid and acid-base balance. In practical terms, if your sodium intake is adequate, chloride follows automatically.
How much of each electrolyte do runners actually need?
There is no universal answer — sweat rates and individual sweat sodium concentrations vary enormously. But there are evidence-based ranges.
Electrolyte needs by running scenario
| Scenario | Sodium (per hour) | Potassium | Magnesium | Notes |
|---|---|---|---|---|
| Easy run, <60 min, cool | 100–200mg | Normal diet | Normal diet | Gel built-in electrolytes sufficient |
| Long run, 90+ min, mild | 300–500mg | 150–300mg | 25–50mg | 40/0.25 gels cover most of this |
| Race-pace or threshold | 400–600mg | 200–300mg | 25–50mg | Consider 40/1.0 gels or add sachet |
| Warm weather running | 500–800mg | 200–300mg | 25–50mg | Add Active Hydration sachet |
| Hot race or heavy sweater | 700–1,000mg+ | 300mg+ | 50mg | Full truefuels system stack |
The truefuels Active Hydration sachet delivers 390mg sodium, 150mg potassium (natural) and 25mg magnesium per 500ml. The Performance Gels carry 288mg potassium and 30mg magnesium per serving alongside the carbohydrate, with sodium content varying by variant (98mg in the 40/0.25, 386mg in the 40/1.0).
The electrolytes you don't need to worry about
Calcium: losses in sweat are minimal and dietary intake almost always covers needs for endurance athletes.
Zinc, iron, selenium: not meaningfully lost through sweat in exercise-relevant quantities. Products including these in electrolyte blends are creating complexity without performance benefit.
Large magnesium doses in sports drinks: adding 60–100mg of magnesium per serving as a "cramp prevention" measure is not well-supported by evidence. It may cause GI discomfort at higher doses.
Electrolyte supplements with 1,000–1,500mg sodium per serving: appropriate only for heavy sweaters in prolonged heat conditions. For most runners in most sessions, this exceeds actual sweat losses and can create GI distress and unnecessary thirst.
The sodium–carbohydrate connection most runners miss
The connection between electrolytes and carbohydrate absorption is more direct than most runners appreciate. Sodium in the intestine enhances glucose uptake via the SGLT1 co-transporter. When sodium is present alongside carbohydrate:
- Glucose uptake increases
- Carbohydrate oxidation improves
- GI distress risk decreases
This is why truefuels builds sodium into its Performance Gels — not as a secondary benefit but as part of how the carbohydrate is delivered. The electrolytes in the gel aren't there because it was convenient to add them. They're there because the carbohydrate works better with them present.
A practical framework
Start with sodium as your planning anchor. Estimate your sweat rate in training by weighing before and after a controlled run. Observe whether your kit shows heavy salt marks — a reliable indicator of above-average sweat sodium concentration. Then set a sodium target that matches your profile and the conditions, and choose a product combination that delivers it cleanly.
For most sessions, the truefuels gel system covers electrolyte needs as part of carbohydrate delivery. For longer efforts in heat, adding the Active Hydration sachet raises sodium intake to match higher sweat losses. For heat racing and training specifically, the full system — gels, electrolytes and CoreCtrl for thermoregulation support — addresses both what you lose through sweat and how effectively your body manages heat under load.
Electrolytes are not complicated. They become complicated when the question is treated as a marketing problem rather than a physiological one. Understand your sweat profile, match your intake to it, and let everything else in your race plan work properly as a result.
