How Your Body Uses Carbs for Training

Think of it like money.

1. Readily available carbs = cash in your pocket
When you eat carbs (toast, banana, sports drink), your body breaks them down into glucose, a simple sugar that goes into your blood. Your muscles can grab it and use it right away. But you only carry about a teaspoon's worth in your blood at any time, so this supply runs out fast.

2. Stored carbs = your savings account
Any glucose you don't use right away gets packed away as glycogen, in two places:

• Muscles: each muscle keeps its own stash for its own work. This is the main fuel tank for training.

• Liver: this keeps your blood sugar steady, so your brain and muscles have a top-up when the cash runs low.

3. What happens during a workout

• Start: your muscles use the glucose in your blood and their own glycogen.

• As you keep going: blood glucose drops, so your liver releases stored glycogen to refill it.

• If you eat or drink carbs during: you're adding fresh cash, so you don't have to dip into savings as fast.

• If the savings run out: this is "hitting the wall." Your legs feel heavy, your pace drops and you feel foggy.

The harder you go, the more carbs you burn. Easy effort uses more fat. Hard effort leans on carbs. Your body can store roughly 90 minutes to 2 hours of hard-effort fuel, and that's why longer sessions call for fueling during, and why refueling afterward matters.

One-line version: carbs you eat go into your blood for quick energy, extra gets stored as glycogen in muscle and liver, and your body spends from both while you train.