Temp Basal
Find out how far ahead of a workout to lower a pump’s basal rate.
Insulin pumps deliver basal insulin as small, continuous pulses of rapid-acting insulin. A temporary basal rate lets you reduce or increase this delivery for a set period of time.
This chart is designed to help you visualize how adjusting your basal rate before, during, and after exercise changes insulin delivery and blood sugar — especially when combined with food and the glucose-lowering effect of exercise itself.
Those pulses are rapid-acting insulin — aspart, lispro, or glulisine — which is what these curves model. A temp basal works precisely because that insulin clears within a few hours; a long-acting basal injection cannot be adjusted the same way. The Bolus Insulin Types simulator compares the curves.
Pay attention to:
- What happens when you reduce basal too late before exercise
- What happens when you reduce it too much or too early
- How does food interact with the temp basal effect
What’s happening here?
Insulin pumps deliver basal insulin as micro-pulses of rapid-acting insulin, unlike MDI users who inject a slow-acting basal insulin once or twice a day. This means pump basal can be adjusted in real time — increased, decreased, or suspended — to respond to changing circumstances like exercise.
A temporary basal rate reduces or increases this ongoing delivery for a set period. Because each micro-pulse of rapid-acting insulin has the same absorption curve as a bolus, the timing of the rate change matters as much as the magnitude.1
Why timing matters
- A temp basal change arrives gradually, not at the moment you set it: it is barely detectable for the first half hour, arriving fastest at around 75 minutes, roughly a fifth of the way there at an hour and half of the way at two
- Setting a temp basal at the start of exercise is often too late — the insulin from the minutes just before exercise is already absorbed and active
- Starting a reduced basal 60–90 minutes before exercise gives part of the change time to arrive before activity begins, and the rest keeps arriving during it2
What happens when basal is reduced
- Less rapid-acting insulin is delivered over time, so the ongoing pull on blood sugar decreases
- Blood sugar tends to drift upward if basal is reduced for long enough
- The exercise-driven glucose uptake partially offsets this rise, but the balance is different for every individual
What happens after exercise
- Returning to normal basal while insulin sensitivity is still elevated can cause a drop
- Some people maintain a reduced basal for 1–2 hours after finishing to account for lingering sensitivity
- Food eaten post-workout will also have a smaller insulin requirement than usual
Applying this to your own life
Temp basals require experimentation, and the same setting rarely suits every workout. Track what happens to blood sugar during and after, and adjust one variable at a time.
- Start modest and early. A 50–70% reduction set 60–90 minutes ahead is a common first setting; adjust from there.
- Judge the whole workout. Was the drop blunted, gone, or replaced by a high? Each answer points to a different adjustment.
- Watch the trend afterward. Note how long blood sugar keeps falling once you stop, and whether a reduced basal after the workout helped.
- Keep notes. When you set the temp basal, by how much, and what blood sugar did during and after.