Get in the Zone: My Tips For Avoiding Hypoglycemia During Exercise

Potential Tactics

Notes

1. Start exercise at a glucose above 140 mg/dl

This provides a buffer to avoid hypoglycemia. You may need to experiment starting at different targets (e.g., 180 vs. 140 mg/dl) to understand what helps you avoid hypoglycemia and end your workouts in your target range.

CGM users should also pay lots of attention to the trend – a pre-exercise value of 140 mg/dl and two down arrows will likely require food, while a 140 mg/dl with two up arrows probably won’t.

If you’re about to exercise and your sugar is too low (e.g., 80 mg/dl), you can eat/drink something. It helps to know exactly how much you need to eat to raise your glucose to your pre-exercise target. For example, I know one glucose tab – 4 g carbs – raises my blood glucose ~20 mg/dl.

2. Reduce bolus insulin

Activity can add to the effects of insulin, meaning a bolus of 1 unit might actually lower glucose like a 2- or 4-unit bolus. You might need anything from a 25%-100% bolus reduction before/during exercise, depending on the activity.

During an endurance activity like cycling, I opt for a 75% reduction in food/correction bolus insulin both before and during exercise.

3. Try reducing basal insulin
(insulin pumpers)

Changes in basal insulin take some time to begin affecting blood glucose – the lag is about 45 minutes to one hour. That means turning down the basal rate before starting exercise (45-60 mins) might be needed to avoid hypoglycemia during exercise. This lag may also require you to resume basal insulin before exercise ends to avoid a high (more on that in section C below). Here’s what this tactic could look like:

2:15 pm: Start reduced basal rate
3 pm: Begin exercise
3:45 pm: Stop reduced basal rate
4:30 pm: End exercise

This time lag means this can be challenging to get right. You need to experiment with the start time, the stop time, and the amount of reduction. [Note: This is also why suspending a pump’s insulin (0% temporary basal) won’t do much to treat a low now; blood sugar will only start rising after ~45 minutes.]

I don’t adjust my basal rate for activities less than 90 minutes, since I find #1 and #2 above are easier for avoiding lows.

4. Don’t eat too close to exercise (aim for at least 30-60 minutes before)

Why? Exercise slows down digestion, so you need to give the food time to get into your system. Eating immediately before exercise means the glucose might not get into the blood until after activity is over. That leads to a double whammy of going low during exercise (food has not been absorbed), and then high after exercise. Gah!

5. Experiment with different foods before exercise

Try different types of carbs (e.g., an apple vs. a slice of toast), different amounts of carbs (e.g., 15 g vs. 45 g), and different timing (e.g., 30 mins vs. 90 mins before) to see what helps you avoid hypoglycemia and stay in range. You ideally want to minimize high fat foods before exercise, since they slow down the absorption of glucose.

This tactic should be done in combination with the bolus reduction strategy discussed above (#2). If you have taken a bolus within two hours of starting exercise, you may need to eat more carbs to counteract the insulin-on-board.

Usually I opt for fruit or oatmeal before endurance exercise; I don’t eat before strength training.

6. Try different foods during exercise

Eating carbs during exercise can help prevent a low from occurring, especially if you are not on a pump (i.e., reducing basal rate is not an option) or are exercising for more than 60 minutes. Again, you want to experiment with type of food (e.g., glucose tabs vs. sports drink vs. energy bar), amount of food (e.g., 15 g vs. 45 g), and timing (e.g., every 30 minutes). It can be helpful to keep low treatments separate from foods that fuel your activity.

Potential Tactics

Notes

1. Try eating more following activity

A mix of high-fiber carbs, protein, and fat after exercise can help keep blood sugar more stable than just carbs alone. Experiment with different foods and meal sizes to find what works for you.

I tend to eat larger meals after more challenging/longer workouts. Some of my common meals after exercise include eggs, frozen berries, an apple with peanut butter, lentils, and/or this smoothie (see bullet #2).

2. Try reducing bolus insulin following activity

You might need bolus reductions of 50% or more to avoid hypoglycemia after exercise – it all depends on how intense the workout was, how much more sensitive to insulin you’ve become, and what you are eating after exercise.

I sometimes use a bolus reduction of 20% for the first meal following intense/long duration exercise.

3. Try reducing basal insulin

A basal insulin reduction after exercise can be helpful for avoiding delayed lows. Many people experience nocturnal hypoglycemia after exercise, so a basal reduction that lasts overnight might also be needed. Like bolus insulin, the amount of basal reduction is highly individualized and could even be 50% or more for many hours following exercise. You need to experiment with the amount of reduction and the timing.

If you’re not on a pump and take a long-acting basal insulin (Lantus, Toujeo, Levemir, Tresiba), reducing your basal dose on exercise days might help you avoid delayed lows.

I don’t usually reduce my basal rate following exercise, since my normal basal rate is set pretty well for the amount of exercise I consistently do.

Potential Tactics

Notes

1. Try eating fewer carbs or changing the type of carb

An obvious and easy-to-address cause of an exercise high is consuming too many carbs before, during, or after exercise. You can also try changing the type of carb to something slightly slower absorbing (e.g., fruit or oatmeal instead of a sports drink/gel).

2. Try a smaller basal insulin reduction or different timing

Timing is everything when it comes to any basal insulin reduction. As noted above, changes in basal insulin take some time to begin affecting blood glucose – I usually find a ~45 minute lag. This is critical for finishing exercise, as you may need to stop the basal insulin reduction before exercise ends. Here’s what this tactic could look like:

2:15 pm: Start reduced basal rate
3 pm: Begin exercise
3:45 pm: Stop reduced basal rate
4:30 pm: End exercise

You might frequently see post-exercise highs if you suspend your pump during exercise. Instead of a 100% basal reduction (pump suspension), it's possible that smaller reductions of 50% or 30% could avoid a post-exercise high. You can also try starting and ending the basal reduction earlier (e.g., in the example above, starting the basal change at 1:45 pm and ending it at 3:15 pm).

3. Add more bolus insulin

It can be dangerous to aggressively dose correction insulin before/during exercise, since activity can add to the effects of insulin. This tactic can be helpful, but must be done with caution and only if you almost always go high after activity. I recommend exercising with a partner if you plan to try adding a lot of bolus insulin. Again, please consult with your healthcare provider before making any changes to your diet, insulin, or medication regimen.​

I will only correct my blood sugar during activity if I’m over 180 mg/dl, and even then, I use only 25% of the normal correction/food dose during endurance exercise.

4. Stay hydrated

Blood sugar levels often go up when the body is dehydrated. Make sure you are drinking enough fluids before, during, and after exercise to replace what is lost through sweat. See “hydration hints” here.

5. Try a different time of day

You may find certain times of day (morning vs. evening) are more likely to raise your blood sugar following exercise. The key is to balance the blood sugar challenges with a schedule that helps you get predictable exercise.

When I do morning exercise on an empty stomach (particularly strength training), I often see a ~20-50 mg/dl rise in my blood sugar; this effect is often not apparent later in the day. For the past few years, I’ve decided to stick with morning exercise, since the convenience and scheduling advantages outweigh the slight blood sugar rise.

Glucose above 100 mg/dl?

Carry:
- Glucose tabs (or other carbs)
- CGM or a blood glucose meter
- A medical alert bracelet (I use this one)
- My phone (in case I need help)

Tell someone where I’m going and for how long

[Check ketones if BG is above 300 mg/dl. Don’t exercise if present.]

Expected BG Change for Walking

Drop of 0-1 mg/dl per minute on flat ground;
Drop of 1-2 mg/dl per minute if insulin was recently taken or if walking uphill.

Time of Day

Any

Food

Before: Eat 5-10 g carbs if lower than 100 mg/dl

During: Glucose tabs (4 g each) or other carbs if trending low. Each glucose tab raises my blood sugar ~20 mg/dl. If my blood sugar is on the lower side of my target range (~100 mg/dl) and I’m walking for longer than 60 minutes, I will eat an apple or other piece of fruit.

After: Nothing different.

Insulin

Bolus: A ~20-30% reduction for a food or correction bolus before/during walking.

Basal: Reduction of 30% only if walking for longer than 90 minutes, starting right when exercise begins and ending 45 minutes before it’s over.

Expected BG Change for Biking, 0-90 mins

Drop of 1-2 mg/dl per minute.

Time of Day

Any

Food

Before:
20 g carbs if blood sugar is under 120 mg/dl
10 g carbs if blood sugar is 120-165 mg/dl
0 g carbs if blood sugar is over 165 mg/dl

24 ounces of fluid (usually water or green tea)

During: Glucose tabs (4 g each) if trending low.

After: Medium-sized meal with 15-30 g carbs, protein, fiber.

Insulin

Bolus: 75% reduction in correction insulin before and during exercise (i.e., from a four unit to a one unit bolus). 75% food bolus reduction if eating more than 20 g carbs. No change in bolus insulin following exercise.

Basal: No change.

Expected BG Change for Biking, 90+ mins

Drop of 1-2 mg/dl per minute.

Time of Day

Any

Food

Before: 60 g carbs (fruit or oatmeal) and 20 g protein (eggs, whey).

During: 16 ounces of Gatorade (~30 g carbs) per hour; glucose tabs when trending low; occasionally I eat a Clif Bar or sandwich (~40 g carbs).

After: Large meal with 30-60 g high-fiber carbs, protein, fat.

Insulin

Bolus: 75% reduction in food and correction insulin before and during activity. 20% food bolus reduction after activity.

Basal: 70% reduction starting when exercise begins and ending one hour before it’s over (e.g., for a 1-4:30 pm bike ride, the 70% basal reduction goes from 1-3:30 pm).

Expected BG Change

No change or a ~20-50 mg/dl rise

Time of Day

Morning

Food

Before: None (I usually train on an empty stomach)

During: None (blood glucose usually doesn’t change or rises)

After: High protein breakfast (eggs, smoothie) and 10-20 g carbs.

Insulin

Bolus: No change

Basal: No change.