Race Day Fuel Plan

Carbohydrate needs are driven by power output and intensity. The carb fraction of total fuel rises sharply with intensity — from ~20% at easy effort to nearly 100% at race pace (~30 g/h at 100 W up to ~190 g/h at 250 W). The gut can typically absorb ~60 g/h from a single carb source, or ~90 g/h with a glucose+fructose mix (SGLT1 + GLUT5 dual transporters). At high power your burn rate exceeds absorption — the deficit can be managed, not eliminated. See the dedicated nutrition calculator for carb-only planning.

Sweat rate ranges from roughly 0.4–0.6 L/h in cool, easy conditions to 1.5–1.8 L/h in hot weather at high intensity. Drink enough to avoid losing more than 2% of your body weight in fluid. Aim for 700–1000 mL per hour and adjust to your sweat rate. The hydration calculator models this in detail.

Sodium is the primary electrolyte lost in sweat, but individual sweat sodium concentration varies widely — from roughly 200 to 1,500 mg per litre. The ACSM recommends 500–700 mg/hour as a starting point. Longer duration, higher intensity, hot weather and salty sweat (white residue on kit) all raise sodium needs.

There is no single optimal ratio — it depends on grams per hour. SGLT1 absorbs glucose (and maltodextrin); GLUT5 absorbs fructose. Up to ~60 g/h, glucose alone saturates SGLT1 and no fructose is needed. Above that, adding fructose opens the second transporter, raising oxidation by up to 50%. Keep glucose at 60–70 g/h, then add fructose to reach your target. Gut adaptation is required above 90 g/h.

Sodium bicarbonate (NaHCO₃, baking soda) is 27.4% sodium by mass: molar mass 84 g/mol, of which sodium is 23 g/mol (23 ÷ 84 = 0.274). So every 1 g delivers ~274 mg of sodium. A typical pre-race load of 0.3 g/kg (≈21 g for a 70 kg rider) adds ~5,750 mg sodium — far beyond hydration needs, so the bicarb dose doubles as a big chunk of your sodium strategy. For comparison: table salt ~393 mg Na/g, sodium citrate ~267 mg Na/g.

Sodium bicarbonate is a blood buffer: it raises plasma bicarbonate, helping neutralise the hydrogen ions that accumulate during hard efforts and delaying fatigue in high-intensity work (~1–10 min bouts repeated through a race). Common protocol: 0.3 g/kg body weight, split into doses with food and water starting ~90 min before the effort. The plan schedules 3 × ~0.1 g/kg every 30 min for shorter, intense races. GI tolerance varies a lot — trial it in training first; enteric-coated forms reduce stomach upset.

Osmolality (mOsm/kg) is the concentration of dissolved particles in your drink, and it controls how fast the drink leaves the stomach and is absorbed. Hypotonic (<275 mOsm) empties fastest — best when fluid replacement is the priority (hot, high sweat). Isotonic (~275–295, matching blood) balances fluid and carb delivery. Hypertonic (>295) would pack more carbs per sip, but it draws water into the gut, slows emptying and can worsen dehydration. The galático bottle recipe reports the mix's mOsm/kg so you can tune it: maltodextrin is a long polymer, so it contributes far fewer particles per gram than glucose or fructose — more carbs at lower osmolality.

A hypertonic drink (>295 mOsm/kg) is more concentrated than blood, so by osmosis it pulls water out of your body into the gut instead of delivering it. That slows gastric emptying, can cause bloating, cramps and diarrhoea, and transiently worsens dehydration — the opposite of what you want in the heat. It's the wrong tool when fluid replacement is the priority. The fix isn't less carbohydrate: split your intake so the bottle stays hypotonic/isotonic for drinking, and take the extra carbs as gels or chews washed down with plain water, which dilute in the stomach. Hypertonic only makes sense in cold weather at very high carb targets where sweat loss is low.

No — nothing new on race day. The single most important rule in race nutrition: every gel, drink mix, electrolyte, caffeine dose and especially the sodium bicarbonate load must be tested in training first. New products on race day risk GI distress, cramping, an unexpected dose response or a flavour you can't stomach mid-effort — bicarb is a notorious gut-upsetter. Rehearse your full plan (carbs/h, fluid, sodium, timing) in long training rides that mimic race intensity and heat, so race day only repeats what your gut already tolerates.