From Bonk to PR: How Smart Nutrition Changes Your Training

You've trained for months. Your fitness is there. But somewhere around mile 18, 20, or 22, your legs turn to jelly and your pace crashes.

You've been hit by the bonk — and it's devastating.

Here's the thing: the bonk isn't always about your training. It's often about your nutrition.

The bonk — or "hitting the wall" — happens when your muscle glycogen stores run dry. Your body has two fuel sources: glycogen (carbs stored in muscle) and fat.

At marathon pace, you're burning mostly glycogen. Your muscles can store about 400–500 grams of glycogen, which translates to roughly 1,600–2,000 calories.

At race pace, you burn through that in 90–120 minutes. Once it's gone, your body can't maintain intensity, and you crash.

Fitness is the engine. Fuel is the gasoline.

You can have the most finely-tuned engine in the world, but if you run out of gas at mile 20, you're not finishing strong.

Proper nutrition during training and racing keeps your glycogen tanks from emptying so your fitness can actually shine through.

• Carb loading before the race to start with full glycogen stores
• Starting fuel early (within 30 minutes) rather than waiting for fatigue
• Maintaining steady carb intake during the race (60–90 g/hour for most)
• Practicing your race fueling in training so your gut knows what to expect

• Eat 3–4 hours before start: 1–4 g carbs/kg body weight
• Include a small amount of protein for blood sugar stability
• Avoid high fiber and fat to protect your gut
• Sip 400–600 ml fluids with electrolytes
• Top off with a small carb snack 30 minutes before the gun

For races over 90 minutes, you need to replace carbs as you burn them.

• Start within 30 minutes of the start — don't wait for fatigue
• Aim for 60–90 g carbs per hour (one gel every 25–30 minutes)
• Pair gels with electrolyte drinks for hydration
• Practice in training so your gut tolerates the load

Your race fueling strategy should be rehearsed in at least three long training sessions before race day.

• Use the same gels, drinks, and timing you plan for race day
• Practice in similar conditions (heat, humidity, terrain)
• Start fueling at the same time you will on race day
• Note any gut distress and adjust products or timing

MAVR takes the guesswork out of bonk-proof nutrition.

• Auto-calculates your carb loading targets based on race distance
• Builds race-day fueling schedules with gel timing and hydration
• Adapts recommendations to your gut tolerance and training history
• Provides daily guidance that keeps you ahead of glycogen depletion