Understanding Energy, Fueling, and How to Avoid the Bonk
Dialing in your nutrition during exercise can feel confusing. Eat too little and you fade hard. Eat too much and your stomach revolts. The key is understanding where your energy actually comes from—and how to replace it before you run out.
Let’s break it down in a simple, practical way so you can fuel smarter and ride stronger.
Where Your Calories Go During a Ride
A straightforward way to estimate calorie burn on the bike is:
Calories burned = Power (watts) × Time (seconds)
For example, riding at 200 watts for one hour burns roughly 720 calories. But those calories don’t come from thin air—they come from stored and consumed energy. And that’s where glycogen comes in.
Glycogen: Your Limited Fuel Tank
Glycogen is a stored carbohydrate—essentially, glucose saved in your muscles and liver for later use. Your body can store about 15 grams of glycogen per kilogram of body weight.
For a 70 kg (155 lb) athlete, that equals roughly 4,200 calories of stored energy. Sounds like a lot… until you look closer.
-
About 400 calories are stored in the liver
-
The rest live in your muscles
-
Muscle glycogen is local—your legs can only use the glycogen stored in your legs
In reality, you only have about 1,100–1,500 usable calories available to power your movement at any given time (assuming you start fully fueled). Once that runs low, performance drops fast. That’s the bonk.
This is also why carb-loading works—it fills that tank as much as possible before you start.
A Real-World Endurance Example
Let’s say you head out for a 4-hour ride at 200 watts.
-
Estimated burn: ~2,900 calories
-
Available glycogen (muscles + liver): ~1,600 calories
That leaves you with a 1,300-calorie gap that must be filled during the ride.
Break that down per hour:
1,300 calories ÷ 4 hours = ~325 calories per hour
Since carbohydrates provide about 4 calories per gram, you’d need roughly:
81 grams of carbs per hour
That amount keeps you from digging deeper into your glycogen reserves—but it doesn’t refill what you’ve already used. If you can tolerate more, say 100 grams of carbs per hour, you not only fuel the ride but also get a head start on recovery.
How much you can handle is individual. That’s why practicing your fueling strategy in training is just as important as training itself.
What This Means for Your Performance
Proper fueling isn’t optional—it’s foundational. Here’s how to apply this in real life:
-
Fuel early and consistently
Waiting until you feel low is too late. Start fueling before glycogen drops. -
Match intake to effort
Long, steady rides and short, intense sessions both rely heavily on carbohydrates. -
Train your gut
Your ability to process carbs improves with practice. Test different amounts during training. -
Recover on purpose
Even with good intra-ride fueling, you’ll still need to replenish glycogen afterward. Prioritize carbs and protein post-ride.
Our Recommendation
For endurance efforts, we suggest:
1½–2 scoops of Redline Endurance Full Throttle per hour of activity
As your tolerance improves, aim for 75–100 grams of carbohydrates per hour to maximize performance, accelerate recovery, and set yourself up to train hard again the next day.
Fueling well isn’t about shortcuts—it’s about respect for the work you’re putting in. When you understand your energy needs and meet them consistently, you ride stronger, recover faster, and keep moving forward—mile after mile.