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High-Intensity Exercise Simulator

See how sprints, heavy lifts, and interval training create a different blood glucose pattern than moderate exercise.

High-intensity exercise above roughly 85% of your maximum heart rate triggers a stress response that temporarily raises blood sugar — even while you are burning fuel at a very high rate. This makes it one of the most counterintuitive situations in diabetes management.

This chart is designed to help you visualize how blood glucose, insulin on board, and insulin sensitivity interact during and after a short, intense workout.

Pay attention to:

For educational purposes only. This simulator is a visual learning tool — not a medical device or dosing calculator.

What's happening here?

During high-intensity exercise, your body releases stress hormones — primarily adrenaline and cortisol — that signal your liver to release stored glucose rapidly. This release outpaces how fast your muscles can use it, so blood sugar rises even though you are working hard.

Unlike moderate exercise, which typically lowers blood sugar during the workout, high-intensity effort can push blood sugar up significantly. The rise often peaks 5-15 minutes after the hardest effort ends, not during it.

Important: The post-workout high is temporary. Giving a large correction bolus during this window can cause a significant low 1-3 hours later as insulin sensitivity spikes during recovery.
Phase 1
During Effort

Stress hormones cause the liver to release glucose faster than muscles can absorb it. Insulin on board is temporarily less effective. Blood sugar rises.

Phase 2
Early Recovery

Stress hormones clear. Blood sugar peaks and begins falling. Insulin on board starts working more effectively — sometimes more than expected.

Phase 3
Late Recovery

Depleted muscles pull glucose from the blood to replenish stores. Insulin sensitivity is significantly elevated. The risk of a delayed low is highest here.

During the workout

  • Stress hormones cause the liver to release glucose faster than muscles can absorb it
  • Insulin on board is less effective than usual — your body is temporarily more resistant to insulin during peak effort
  • Subcutaneous insulin may absorb slightly slower during peak effort due to reduced skin blood flow

Immediately after (0-60 minutes)

  • Stress hormones begin to clear, and blood sugar starts falling from its peak
  • Insulin on board begins working more effectively as resistance fades
  • Any correction bolus given for the post-workout high will act faster and stronger than it would at rest

Later after (1-6 hours)

  • Muscles that were depleted during the workout begin pulling glucose to replenish their stores — with or without insulin
  • Insulin sensitivity is significantly elevated, meaning the same dose lowers blood sugar much more than usual
  • This is the window where a correction given for the earlier high can cause a significant low

The day after

  • Insulin sensitivity can remain elevated for up to 24-48 hours after intense exercise
  • Meals and corrections during this window may need smaller doses than usual

Applying this to your own life

High-intensity workouts create two separate management challenges that happen back to back: a high during and just after the effort, followed by an elevated low risk in the hours that follow.

When doing intense workouts, watch how your blood sugar responds during the workout itself and for several hours afterward. A CGM is especially useful here because the delayed low can happen well after the workout feels finished.

As you make observations, keep notes on:

  • How high your blood sugar rises and how long the peak lasts after you finish
  • How quickly it falls in the first hour after you stop
  • Whether you notice lows 2-6 hours later, and whether they happen during sleep if you worked out in the evening
  • How your next meal's insulin needs compare to a day when you didn't work out