Whether you are at the gym, taking a stroll at a park or actively doing household chores, exercise affects your blood glucose.
Physical activity can raise or lower your blood glucose so frequent monitoring and adjustments will be necessary to maintain a safe level. This is especially important if you start or change your exercise routine.
Continuous, light-to moderate intensity exercise and includes activities like running, walking, long-distance swimming, biking or tennis
Aerobic exercise typically tends to lower BGLs.
Shorter in duration, of maximal to super max intensity and includes activities like sprinting, gymnastic, ice hockey, or weight training
Anaerobic exercise typically tends to raise BGLs.
Combination of the aerobic and anaerobic activity such as basketball or soccer.
Time of Day
The time of day which you exercise can affect how your blood sugars respond. For some, the hormones our bodies produce early in the morning will cause insulin to be less effective, so you may have a very different response in the morning compared to the exact same exercise routine done later in the day. Exercise performed at night may increase your sensitivity to insulin. For those who take insulin, this may put you at risk for hypoglycemia in the middle of the night.
Intensity of Activity
You may also notice the type of activity you perform will affect you differently. Intense exercise (weight lifting/sprinting) can cause your BG to rise during the activity and it may stay elevated for 1-2 hours afterward. This is due to the hormones being released (adrenaline) which work against insulin action. If you take insulin, you may need a bit more insulin prior to or after activity to compensate for this.
Mild to moderate activities generally drop the BG during the activity. Depending on how long you plan to perform the exercise, you may need a small snack prior to exercise or, if you take insulin, you may need to decrease your insulin dose prior to/during activity.
The more intense and longer you exercise, the greater your risk for delayed hypoglycemia. Your body will re-stock spent glycogen (stored carbohydrate in liver & muscles) over the next few hours (for extreme exercisers, this can take up to 3 days!) by pulling it from the bloodstream, potentially causing a delayed onset of hypoglycemia.
Strategies to avoid Hypoglycemia
- Use of temporary basal rates is on an insulin pump
- Reduction of meal/correction bolus w/in 1-2 hr of exercise
- Try to exercise in the morning or afternoon to avoid overnight lows. If exercising in the evening, you may need 15-30g carb at bedtime as a precautionary measure.
- Have a carbohydrate source available at all times, 30-60 grams carbohydrate for every 30-60 minutes of exercise & adjust as needed
- Check blood glucose before, during (for longer bouts of exercise) and after exercise
Palo Alto Medical Foundation: Pre Pump Education Packet