How do I avoid bonking on long rides?

Bonking is the sudden drop in power, mood, and coordination that happens when blood glucose dips and muscle glycogen runs low. The fix isnt mystical. Its smart glycogen management and consistent mid-ride fueling. Heres how to keep watts stable from the first climb to the last kilometer.

Glycogen 101: what drives the bonk

Your body stores carbohydrate as glycogen in muscle and liver. A trained rider has roughly 40050 g available (about 1,600600 kcal), but how fast you burn it depends on intensity.

• Endurance/Zone 2 (5575% FTP): higher fat contribution; glycogen lasts longer.
• Tempo to threshold (8098% FTP): carbohydrate use ramps sharply; repeated surges drain stores.
• Above threshold/VO2: mostly carbohydrate; glycogen drops quickly.

Classic bonk warning signs include irritability, lightheadedness, chills, a hard-to-turn pedal stroke, and suddenly needing to sit on. If you sense these, take in 2030 g fast carbs and back off intensity for 1015 minutes.

Use your power meter or head unit: total kJ roughly tracks total kcal burned on the bike. If youre burning 600900 kJ per hour, youll never replace it all in real time, but matching a solid fraction with carbs and fluids keeps glycogen and blood glucose in the safe zone.

Key idea: ride within yourself, avoid unnecessary surges, and start fueling earlybefore you feel hungry or slow.

Mid-ride fueling: grams per hour that work

Carbohydrate targets depend on duration, intensity, and how well your gut is trained. Most riders underfuel. Use these ranges as a starting point and adjust after a few rides.

Tips that make those numbers doable:

• Start early: take 2030 g within the first 2030 minutes, then drip-feed every 1015 minutes.
• Mix carb types: combine glucose/maltodextrin with fructose to push intake toward 90120 g/h if needed.
• Keep drinks isotonic: 68% carbohydrate (6080 g per liter) improves absorption, especially in the heat.
• Solid-to-liquid shift: eat more solids (bars, rice cakes, bananas) in the first half, favor gels/chews and drink mix later when intensity or gut fatigue rises.
• Fuel the efforts: if the ride includes long tempo/threshold pulls, add 1020 g around those segments.

What 20120 g of carbs looks like:

• Gel: 2030 g
• Chews: 2025 g per serving
• Half bar: 1525 g (full bar 3045 g)
• Banana: ~25 g
• 500 ml of 6% drink: ~30 g

Pre-ride matters:

• 24 hours before: 12 g/kg of low-fiber carbs plus some protein; drink 500700 ml with sodium.
• 15 minutes before: 2030 g quick carbs if its a long or steady ride.

Post-ride for recovery and next-day glycogen: 1.01.2 g/kg/h carbs for 24 hours (or a high-carb meal ASAP) plus 2040 g protein.

Hydration, sodium, and a gut that can handle it

Hydration isnt just about water. Carbs and sodium improve fluid absorption and help keep blood volume stable so you can keep pushing watts.

• Fluids: aim for 0.40.8 L/h (cool to hot conditions). In high heat or if youre large, you may need more.
• Sodium: 400800 mg/h covers most riders; very salty sweaters may need 8001200 mg/h. Spread it across bottles and foods.
• Check sweat rate: weigh yourself before and after a 6090 min ride. Each 1 kg lost 7 ~1 L sweat. Target losses under 2% of body mass.
• Post-ride rehydration: replace ~150% of fluid lost over the next few hours (add sodium to keep it in).

Train your gut like you train your legs:

1. Pick your target (for example, 75 g/h) and practice it on endurance rides.
2. Use a timer every 15 minutes; steady intake beats big dumps.
3. Increase by 1015 g/h each week until you reach your goal or your gut says stop.
4. Keep mixes isotonic; avoid stacking multiple concentrated products in the same hour.

Common mistakes to avoid:

• Starting to eat after the first hour too late.
• Only drinking water on hot days.
• Spiking effort above threshold repeatedly on an endurance ride.
• Relying on high-fiber/fatty snacks that slow gastric emptying.
• Running out of supplies; bring one extra gel or bar and an extra electrolyte stash.

Example: 4-hour endurance/tempo ride (6575% FTP)

Target 8090 g carbs/h, ~0.60.8 L/h fluid, 600900 mg sodium/h.

• Each hour: one 60050 ml bottle with 4060 g carbs + 400600 mg sodium, one gel (25 g), and ~20 g from bar/chews. Thats ~85105 g/h total.
• Set a 15-minute alert: sip bottle continuously; alternate gel and bar bites so you never go 15 minutes without intake.
• If you insert a 20-minute tempo pull, add 1015 g extra carbs in the 10 minutes before or after.

With consistent pacing and a simple plan, youll keep glycogen topped up, avoid the bonk, and finish your long rides feeling strongnot surviving to the line.