Extended Exercise Simulator

Model blood glucose across a 4-hour workout: pre-exercise preparation, in-exercise fueling, and post-workout recovery.

Long workouts lasting four or more hours deplete glycogen stores, increase insulin sensitivity, and require active fueling strategies to maintain blood glucose. The effects extend well beyond the exercise window itself.

This chart is designed to help you visualize how pre-exercise fueling, in-exercise nutrition, pump temp basals, and post-exercise recovery all interact across the full timeline of a long workout.

Pay attention to:

What happens when pre-exercise fueling is low or insulin on board is high?
How does continuous in-exercise fueling change the curve during the workout?
What does the post-exercise persistent decline look like, and why does it matter overnight?

What's happening here?

Extended exercise changes how insulin and carbohydrates behave in your body. Muscles need carbohydrates to keep working. During moderate aerobic activity, muscle cells can absorb glucose without needing insulin, which means your blood sugar can drop quickly — especially if you have insulin on board.

Important: You must always have some insulin in your body to avoid DKA, which is caused by a lack of insulin — not high blood sugar.

Phase 1

Before Exercise

Fueling before a long workout tops off glycogen stores. Carbohydrates are stored as glycogen, and once those stores run low, performance drops.

Phase 2

During Exercise

Aerobic activity increases insulin sensitivity. The same insulin lowers blood sugar more than usual. Insulin on board has a much larger effect.

Phase 3

After Exercise

Muscles and liver continue pulling glucose to replenish depleted glycogen. Increased insulin sensitivity can last many hours — sometimes up to 24 hours.

During exercise (4 hours)

The same amount of insulin lowers blood sugar more than usual.
If fueling is too low, blood sugar may drop steadily throughout the workout.
If fueling matches muscle demand and insulin is appropriately adjusted, blood sugar may stay stable.

After exercise (post-workout)

Blood sugars trending lower in the hours after finishing.
Reduced insulin needs for meals eaten after exercise.
Increased risk of delayed lows, especially overnight.

MDI vs Pump

MDI users rely on long-acting basal insulin, which cannot be adjusted quickly. Pump users can adjust basal rates, but changes take time due to absorption. This is why temp basal reductions often need to start 90–120 minutes before exercise begins.

Applying this to your own life

Extended workouts require planning in three phases:

Before: Evaluate insulin on board, adjust pump basal early if needed, fuel to support glycogen stores.
During: Fuel regularly, monitor trends, remember less insulin is needed but not zero insulin.
After: Expect increased insulin sensitivity, consider reduced bolus doses, watch for delayed lows especially overnight.