Have you ever had this experience?

I'd been cycling for over an hour. For the first hour, my legs felt strong; I could even stand up and swing them a couple of times on hills. Then, around 1 hour and 20 minutes in, something strange happened. My legs suddenly went weak—not the kind of weakness from being tired, but the kind where I couldn't muster any power to pedal. On the same stretch of road, where I could easily maintain a speed of 30 km/h, I could only manage 26 km/h no matter how hard I tried.

After that, my mind started to fog up. Seeing a roadside convenience store, all I could think about was, "Do they sell bananas?"

If you've ever had this experience, congratulations—you've hit a wall.

And the timing of hitting that wall is strikingly consistent: around 90 minutes. This isn't a coincidence. It's your body's physiological limit, the first ironclad rule of cycling nutrition. Today, we'll thoroughly explain this "90 minutes."

I. Your Body Actually Has Two Fuel Tanks

Imagine the human body as a hybrid car to better understand this.

You have two fuel tanks in your body.

The first fuel tank: Carbohydrates (glycogen)

This tank contains "high-octane gasoline." It's powerful, burns quickly, and provides instant power with a tap of the accelerator. Climbing hills, sprinting, and breaking through enemy lines all rely on it. But this fuel tank isn't large. A normal adult with a normal diet and weighing around 70 kg has approximately 800 to 1000 calories stored in their muscles and liver.

What does 800 to 1000 calories mean? It's roughly equivalent to:

4 bowls of rice or 8 bananas or 3 McDonald's hamburgers. Sounds like a lot? But an hour of high-intensity cycling can burn 500 to 800 calories. In other words, if you cycle aggressively enough, this fuel tank will be low in less than two hours.

The second fuel tank: Fat

This tank contains "diesel." The reserves are virtually unlimited—even a seemingly thin cyclist has enough fat stored up to sustain them for hundreds of kilometers.

But the problem is: fat burns too slowly.

If carbohydrates are like lightning that explodes at the touch of a switch, fat is like a match that needs to be lit slowly. It lets you keep riding, but it doesn't let you ride fast. When your body switches to pure fat-burning mode, your power output drops drastically, leaving only the bare minimum to "keep going." This is the essence of "hitting the wall": the high-octane gasoline runs out, you're forced to burn diesel, and then you find yourself unable to go any further.

II. Why exactly 90 minutes?

First 30 minutes: Primarily relying on muscle glycogen, blood sugar is stable, with a small amount of fat used. You feel full of energy.

30-60 minutes: Glycogen levels drop, and the body begins to increase the proportion of fat used for energy. As long as the intensity isn't too high, performance isn't affected.

60-90 minutes: The critical window. Liver glycogen is used to maintain blood sugar, and muscle glycogen is more than half depleted. The proportion of fat used for energy increases, but the output power decreases. You might still feel energetic, but you just can't go fast.

90-120 minutes: Glycogen is depleted. If carbohydrates haven't been replenished, the body forces itself into "energy-saving mode." Fat becomes the primary fuel, power drops drastically, the brain becomes confused due to lack of sugar, and limbs feel weak.

Therefore, the 90-minute figure represents a physiological boundary derived by dividing the volume of your body's two fuel tanks by your output power.

III. But this "90 minutes" is not fixed.

Variable 1: Intensity

A leisurely ride might last up to 2 hours before you run out of energy. But if you're aiming for a high-scoring route or joining a group that pushes the limits, you might be exhausted after just over an hour.

Variable 2: What you ate the day before

If you ate well the day before, your glycogen stores will be full in the morning, pushing the 90-minute mark further back. If you only ate a salad for dinner, you might start feeling unwell after 45 minutes.

Variable 3: Individual metabolic differences

Some people are naturally better at burning fat. Cyclists who engage in long-term low-intensity training are more efficient at using fat for energy and can endure longer before hitting the wall.

IV. What should I eat at 90 minutes?

Now that we know 90 minutes is the critical point, the strategy is clear:

<90 minutes: A quick bite before heading out is enough. A banana, a slice of bread, or even an empty stomach will suffice—as long as you ate enough the day before.

>90 minutes: You must actively replenish carbohydrates before the 90-minute mark.

Note the word "before." Don't wait until your legs feel weak to eat; by then it's too late. Once blood sugar drops, it takes at least 20 minutes to pull it back up, and those 20 minutes will be extremely painful for you while cycling.

The correct approach: Start replenishing carbohydrates in small bites from the 45th to 60th minute.

What to eat?

Bananas: Natural energy gel, easily digestible, contains potassium to prevent cramps.

Energy gels: Specially designed for exercise, absorbed quickly.

Rice cakes/rice balls: A blessing for Asian stomachs, digested at a moderate speed.

Energy gummies: Can be eaten as a snack, but not as a main meal.

How much?

Simple formula: 40-60 grams of carbohydrates per hour

40-60 grams ≈ 1.5 bananas ≈ 2 packets of energy gels ≈ a small bowl of rice

V. In the Data Age, How to Precisely Avoid Pitfalls?

The "90 minutes" and "40-60 grams" figures above are averages. But are you an average?

This is where data comes in handy.

Heart Rate Data: If your output power is the same, but your heart rate inexplicably spikes, it might be a sign of glycogen deficiency.

Power Output Data: If your power output starts to drop, and you don't actively slow down, it means you're running low on fuel.

Ride Duration: Your bike computer clearly shows how long you've ridden. At the 60-minute mark, the bike computer vibrates to remind you "time to eat." It's not high-tech; it's just a timer, but it works.

Coospo always says that what they do is not just record how fast and how far you ride, but help you understand your body. Those heart rate curves, power output data, and ride durations are not just material for social media posts, but a language for you to communicate with your body.

VI. Finally, a Lighthearted Remark

 Many experienced cyclists develop a kind of "body awareness" after riding tens of thousands of kilometers. No need to look at the odometer or the time; at a certain point in your ride, you suddenly feel, "It's time to eat." But upon closer inspection, that feeling usually appears around the 90-minute mark. Your body will always react faster than your brain. When glycogen is almost depleted, it will tell you through leg weakness, decreased power output, and mental fog: "Hey, it's time to refuel." What you need to do is actively refuel it before that moment arrives.

VII. Coospo's Tips

If you plan to ride a long distance tomorrow, try this:

Before setting off: Eat a banana or a slice of bread (200-300 calories is enough)

45 minutes: Start considering, "Should I eat something?"

60 minutes: Eat your first meal (half a banana/a packet of energy gels)

90 minutes: Eat your second meal, the new fuel is ready.

After the ride: Don't worry about calories, eat whatever you want, you deserve it.

You'll find that, for the same distance and the same route, this time you'll still feel energetic and happy. This is the magic of supplies. It's also a concept Coospo wants to convey:

Understanding a little science isn't to make riding harder, but to make riding more enjoyable. Because riding enjoyable is what makes it cool.