Exercise Timing Simulator
For aerobic and low-to-moderate intensity exercise: see how food and insulin timing interact with the glucose-lowering effects of a workout.
Exercise causes muscles to absorb glucose directly — with or without insulin. That means blood sugar can drop during a workout even if you have no insulin on board. When you do have insulin active, exercise amplifies its effect.
This chart is designed to help you visualize how the timing of food and insulin around exercise changes the blood sugar curve before, during, and after a workout.
Pay attention to:
- What happens when you start exercise with insulin on board?
- What happens when you eat carbs before exercise without taking insulin?
- How does the timing of food and your bolus change the curve before, during, and after?
- For high-intensity interval training and sprints, see the High-Intensity Exercise simulator
What's happening here?
During aerobic exercise, your muscles can absorb glucose without insulin — a direct, insulin-independent uptake that causes blood sugar to drop regardless of how much insulin is on board. The harder and longer you exercise, the more pronounced this effect.
When you also have insulin active during exercise, the two effects compound. Exercise accelerates insulin absorption from the injection site, meaning insulin peaks sooner and acts more strongly than it would at rest. This combination — glucose uptake by muscle plus faster-acting insulin — can cause a rapid drop.
Before exercise
- A large bolus 1-2 hours before a workout will still be near its peak when exercise starts, compounding the glucose drop
- Eating carbs without a bolus can raise blood sugar before exercise, which then acts as a buffer against the exercise-driven drop
- Starting exercise with no insulin on board and no food means blood sugar may drop from muscle uptake alone
During exercise
- Blood sugar typically falls throughout the workout, faster if insulin is active
- Fueling with fast-acting carbs during the workout can offset the drop
- The rate of drop depends heavily on how much insulin was taken before and when
After exercise
- Insulin sensitivity remains elevated for hours after a workout — sometimes up to 24 hours
- The same dose of insulin lowers blood sugar more than it would at rest
- Meals and corrections in the hours after exercise often need to be smaller than usual
Applying this to your own life
Watch what happens to your blood sugar in the 2-3 hours before, during, and after workouts. The patterns repeat, but they depend on how much insulin is on board when you start.
Keep notes on:
- What your blood sugar does during different types of workouts
- Whether pre-workout carbs help keep blood sugar stable, and how much
- Whether you notice lows 2-6 hours after exercising — this is the elevated sensitivity window