Carb Loading & Sodium Before Race Day: Stop Guessing

You trained for months. Don't sabotage it with random fibre and panic salt tablets. Race week nutrition is not the time for experimentation. It's the time for precision.

Glycogen supercompensation: the science behind carb loading

Glycogen supercompensation is the process of elevating muscle glycogen stores above their normal resting levels through a combination of tapered training and increased carbohydrate intake. When executed correctly, it can increase glycogen stores by 50 to 100% above baseline levels (Hawley et al., 1997).

The modern protocol: 8 to 12 g carbohydrate per kg body weight per day for 36 to 48 hours before race start. Combined with a significant reduction in training volume, this approach maximises glycogen storage without the gastrointestinal distress and psychological burden of older depletion-loading protocols.

For a 70 kg athlete, this translates to 560 to 840 g of carbohydrate per day. That is a substantial volume of food. Practical execution requires deliberate food selection: white rice, pasta, bread, potatoes, fruit juice, and honey are staples. Fibre should be minimised in the final 24 hours to reduce GI bulk on race morning.

For the underlying science of carbohydrate absorption and transport, see high-carbohydrate fueling strategy.

Weight gain: the signal, not the problem

Every gram of glycogen is stored with approximately 3 grams of water. An effective carb load will result in 1 to 3 kg of temporary weight gain. This is not fat. It is stored fuel and improved hydration status.

Athletes who panic at the scale during carb loading and reduce intake are undermining the entire purpose of the protocol. The weight gain is the confirmation that it is working. Treat it as a positive signal.

Sodium preloading: context, not protocol

Sodium preloading has gained attention as a race-week strategy, and there is physiological rationale for it. Increasing sodium intake in the 12 to 24 hours before racing supports plasma volume expansion, which can benefit thermoregulation and cardiovascular stability during prolonged exercise in heat (Sims et al., 2007).

However, sodium preloading is contextual. It is most relevant for hot-weather events (Australian Ironmans in December, for example) and for athletes with high individual sweat sodium concentrations. It is not a universal requirement, and blanket recommendations of fixed milligram doses without considering individual variability are incomplete.

Understanding how much sodium you actually need during exercise provides the foundation for making informed decisions about pre-race sodium strategy.

Morning-of fueling: the final top-up

Target: 1 to 2 g/kg of easily digestible carbohydrate, consumed 2 to 3 hours before race start.

The purpose of morning-of fueling is to replenish liver glycogen, which is depleted overnight during fasting. Muscle glycogen remains elevated from the carb load, but liver stores need topping up to maintain blood glucose availability during the early stages of the race.

Food choices should be low-fibre, low-fat, and familiar. White toast with honey, white rice, or a liquid carbohydrate source are common options. Hydrax Primer is formulated for this exact pre-race window: concentrated carbohydrate delivery with minimal gastric volume, reducing the risk of GI distress on the start line.

GI risk management on race day

Gastrointestinal distress is the leading cause of DNF in Ironman-distance racing, and it is almost entirely preventable with proper planning. The primary risk factors are: excessive fibre in the 24 hours before racing, unfamiliar foods on race morning, and consuming fuels with high osmolality during the event.

Understanding why osmolality matters for performance is critical for selecting fuels that work with your gut under race-day stress.

During the race: executing the fueling plan

Once the race begins, the carb loading phase is behind you. Now it becomes about maintaining exogenous carbohydrate delivery at 60 to 90 g per hour (for events exceeding 2.5 hours) and replacing sodium at 500 to 1,000 mg per hour.

Hydrax Core delivers 85 g of dual-source carbohydrate and ~980 mg sodium per serving through a maltodextrin-fructose formulation that utilises separate intestinal transport pathways (SGLT1 and GLUT5), maximising absorption while maintaining low osmolality for gut tolerance.

The metabolic demands of high-intensity segments, particularly during the run leg of a triathlon, are explored in our article on understanding lactate and VO₂ threshold.

Summary

• Carb load: 8 to 12 g/kg/day for 36 to 48 hours pre-race
• Expect 1 to 3 kg weight gain from glycogen-bound water
• Sodium preload contextually for hot-weather events
• Morning-of: 1 to 2 g/kg low-fibre carbohydrate, 2 to 3 hours pre-start
• During race: 60 to 90 g/hr carbohydrate, 500 to 1,000 mg/hr sodium

Fuel intentionally. Train better.

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