Preventing Low Glucose During and After Exercise

Low blood sugar (hypoglycemia) is one of the most common and concerning challenges for active people with diabetes, especially those using insulin or glucose-lowering medications. By employing effective strategies, you can significantly reduce your risk of experiencing lows during and after activity. Here, we show how to prevent low glucose during and after exercise.

⚠️ When Are You Most at Risk for Exercise Lows?

Understanding the risks of exercise-induced hypoglycemia is essential for maintaining your safety and optimal performance. You may not be aware that your body is most susceptible to dropping glucose levels under specific conditions. Here are key scenarios to watch out for:

Starting with a Low Glucose: If your glucose levels are low or trending downward on your continuous glucose monitor (CGM), be extremely cautious before engaging in physical activity.
Excess Insulin on Board: Recent bolus insulin can lead to excess levels that may contribute to hypoglycemia during exercise. Always keep track of your IOB.
Previous Low Episodes: If you’ve experienced a moderate to severe low blood glucose incident in the past 24 to 36 hours, your body might be more vulnerable to another drop during exercise.
Spontaneous or Prolonged Exercise: Engaging in exercise on a whim or participating in prolonged activities involving untrained muscles, can increase your risk.
New Activities or Increased Intensity: Trying a new workout or pushing yourself harder than usual can surprise your body and lead to unplanned lows.
Challenging Weather Conditions: Cold weather or unpredictable conditions can complicate your body’s response to exercise, making it more prone to hypoglycemia.
Insulin Excess: If you haven’t reduced your basal or bolus insulin, your chances of experiencing hypoglycemia rise significantly.
Post-Illness or Untrained Muscles: After recovering from illness or periods of inactivity, smaller glycogen stores make it more susceptible to have a low blood sugar during or following exercise.

Stay informed and proactive about your health! By understanding these common triggers and keeping up with the latest research, you can better prepare for your workouts. Being mindful of your body’s signals and adjusting your routine can help prevent exercise hypoglycemia and ensure you enjoy a safe and effective exercise experience. Don’t let an unexpected low hold you back from achieving your fitness goals!

How to Prevent Hypoglycemia Before, During, and After Exercise

🔍 1. Pre-Exercise Strategies

Start with a safe glucose level: Ideallybetween 90 and 180 mg/dL, trending stable or slightly upward.
Check glucose trend and IOB: Check your CGM trend and pump insulin on board (IOB).
Use Exercise Mode or a temporary basal: Start this 60 to 120 minutes before activity for AID or pump users.
Reduce bolus insulin: For meals within two hours of exercise, lower the dose by 30 to 50% depending on intensity.
Consume fast-acting carbs if your glucose is below 90 mg/dL or if your IOB is high.
Avoid starting activity if you have recently experienced a low: Your counter-regulatory responses may be diminished.

🚶‍♂️ 2. During Exercise Tips

Monitor your glucose every 30–60 minutes (more often during intense or long workouts)
Carry fast carbs with you: glucose tabs, juice, sports drinks, gummies, or candy
Use the ExCarb system: Know how many grams of carb your body will burn based on the activity

Example: A 150 lb person running 6 mph for an hour may burn ~50g of carbs</em >
Eat small amounts of carbs during prolonged activity: Every 45 minutes is a good rule of thumb
Pay attention to symptoms: If you’re sweating, shaky, or confused, treat immediately—even if the CGM looks fine

Fast Glycogen Rebuilding Reduces Delayed Hypoglycemia
After prolonged or strenuous exercise, it’s essential to quickly rebuild muscle glycogen once the activity stops. There is a 20- to 30-minute window following exercise during which muscles are ready to restore depleted glycogen. Consuming carbohydrates and protein for muscle repair immediately after exercise helps facilitate the rapid rebuilding of muscle glycogen stores. Chocolate milk provides a convenient way to offer both carbohydrates and protein right after exercise. Quick glycogen replenishment after exercise decreases glucose depletion from the blood in the hours that follow and reduces the risk of nighttime lows. Consuming carbohydrates post-exercise replenishes glycogen and readies you for the next day’s workouts. A smaller carbohydrate dose to account for this intake enhances glycogen absorption. Higher carbohydrate intake increases muscle glycogen storage, enhancing endurance and performance. On a high-carb diet, a trained marathon runner can sustain running for about four hours before experiencing exhaustion. Many athletes “fuel up” their muscle glycogen stores to improve performance by consuming a high-carb meal accompanied by a carbohydrate bolus the evening before significant exercise events.

Fast Glycogen Rebuilding Reduces Delayed Hypoglycemia

After prolonged or strenuous exercise, it’s essential to quickly rebuild muscle glycogen once the activity stops. There is a 20- to 30-minute window following exercise during which muscles are ready to restore depleted glycogen. Consuming carbohydrates and protein for muscle repair immediately after exercise helps facilitate the rapid rebuilding of muscle glycogen stores. Chocolate milk provides a convenient way to offer both carbohydrates and protein right after exercise.
Quick glycogen replenishment after exercise decreases glucose depletion from the blood in the hours that follow and reduces the risk of nighttime lows. Consuming carbohydrates post-exercise replenishes glycogen and readies you for the next day’s workouts. A smaller carbohydrate dose to account for this intake enhances glycogen absorption.
Higher carbohydrate intake increases muscle glycogen storage, enhancing endurance and performance. On a high-carb diet, a trained marathon runner can sustain running for about four hours before experiencing exhaustion. Many athletes “fuel up” their muscle glycogen stores to improve performance by consuming a high-carb meal accompanied by a carbohydrate bolus the evening before significant exercise events.

Excerpt from Pumping Insulin with Automated Insulin Delivery

🌙 3. After Exercise: Preventing Delayed Lows

Exercise can cause glucose to fall 6 to 36 hours later, particularly at night, due to:

Rebuilding glycogen stores in muscle and liver
Increased insulin sensitivity
Ongoing low-level muscle glucose uptake

💡 Strategies to avoid overnight lows:

Eat extra slow-acting carbs at dinner or bedtime
Reduce basal insulin by 10–40% for 6–12 hours (use temp basal if on a pump or AID system)
Consider an extended Exercise Mode overnight on your AID system
Set CGM alerts a little higher (e.g., 90 mg/dL low threshold)
For strenuous or long-duration activities, monitor trends into the next day

🧠 Muscle Memory and Hypoglycemia

When starting a new activity (e.g., gardening, canoeing, or snow shoveling), muscles absorb more glucose to prepare for future efforts. This glycogen-loading phase can pull glucose from the blood for several hours, increasing the risk of lows—especially at night. Once an activity becomes routine, this effect stabilizes.