Exercising with Diabetes

When exercising with diabetes, Extra Carbohydrates, or ExCarbs, provide the yardstick for measuring the impact an exercise will have on blood sugars. For more detailed information on exercising with diabetes while on a Pump and AID, look at Chapter 18 of Pumping Insulin with Automated Insulin Delivery.

Diabetes doesn’t have to stop you from staying fit or enjoying sports. With proper planning and monitoring, many people with diabetes thrive in athletics—from casual walks to endurance events. Groups like Team Type 1 prove that diabetes can’t hold you back when your blood sugar is managed effectively.

Why Exercise Matters for People with Diabetes

Exercise sharpens the mind, tones the body, strengthens the heart, increases endurance, reduces stress and fatigue, and combats depression. Most importantly, it significantly improves blood glucose control and reduces insulin resistance. How much exercise is enough? Start where you are, and then build up. The goal is 30 minutes of moderate activity most days, but every bit counts.

Bonus: Regular activity reduces your risk of cardiovascular disease by up to 70% and extends life expectancy—according to data from long-term studies like the Health Professionals Follow-Up Study.

Exercise Planning Based on Your Goals

🧠 Note: Estimate max heart rate: 220 – your age. Or use the talk test:

• Light = can talk easily
• Moderate = can talk, not sing
• Vigorous = short phrases only

How Exercise Affects Blood Sugar

Exercise typically requires changes to basal and bolus doses to maintain stable glucose levels. Insulin adjustments are more effective for planned activities, but many are unplanned and require adjustments during or after the activity. Factors that influence how your blood sugar reacts include:

• Starting glucose and trend from Continuous Glucose Monitor (CGM)
• Active insulin or Insulin on Board (IOB)
• Carb intake and residual carbs on board
• Type, intensity, and duration of activity
• Level of training or fitness
• Meal timing
• Stress hormone response (especially in competition)

Insulin and Carb Adjustments for Exercise

Exercise increases insulin sensitivity, meaning your body needs less insulin to process glucose. Without adjustments, this can lead to lows during or hours later.

🔧 Key Adjustments May Include:

• Reducing basal insulin (start 1.5–3 hours before)
• Lowering bolus insulin (for meals before activity)
• Using ExCarbs to estimate extra carb needs
• Raising glucose targets via AID “Exercise Mode”

🧠 AID systems respond to trends but don’t anticipate activity. Manual insulin adjustments are still essential for best results.

Using ExCarbs: A Smarter Way to Cover Exercise

ExCarbs = Estimated Carbohydrates needed to fuel exercise.

The number depends on:

• Your weight
• Exercise intensity
• Duration

🏃‍♂️ Example: A 150 lb person jogging for 1 hour at 6 mph needs about 50g of carbs.

You can cover ExCarbs by:

• Eating free carbs
• Reducing bolus insulin
• Reducing basal insulin
• A combination of the above

Formula:
ExCarbs ÷ CarbF = insulin units to reduce

💡 Tables available at the end of this article estimate ExCarbs for hundreds of activity types and intensities.

Why Glucose Sometimes Rises During or After Exercise

Glucose usually drops, but it can rise due to:

1. High-intensity anaerobic activity
2. Stress hormones during competition
3. Dehydration
4. Low pre-exercise insulin levels

🔁 Solution: Use insulin corrections, or reduce pre-activity insulin doses and rely on well-timed carb intake.

Preventing Low Blood Sugar During and After Exercise

Low blood sugar (hypoglycemia) is one of the most common and concerning challenges for people with diabetes who are active—especially those using insulin or glucose-lowering medications. With the right strategies, you can greatly reduce your risk of lows during activity and in the hours or days afterward.

Risk factors for lows:

• Lower starting glucose
• Downward CGM trend
• High IOB
• Prior hypoglycemia
• Untrained muscles
• Longer or spontaneous activity
• Overnight glycogen replenishment

Prevention strategies:

• Reduce insulin (bolus and/or basal)
• Start with higher glucose or raise CGM target
• Use fast carbs during activity (e.g., glucose tabs, juice)
• Use slower-digesting carbs post-exercise
• Recheck CGM frequently for delayed lows (especially overnight)

Understanding Fuel Use: Glucose vs. Fat

• Short/intense efforts burn glucose first
• Long/steady efforts shift toward fat as fuel
• Untrained muscles consume more glucose
• Well-trained muscles store more glycogen and spare glucose

Insulin Must Be Low to Burn Fat Efficiently

High insulin blocks fat usage and forces reliance on carbs to avoid lows.

🧠 Even lean people have 2,000x more energy in fat stores than glucose stores!

Exercise Timing and Blood Sugar Trends

• Morning (fasted) workouts may raise glucose if insulin is too low
• Post-meal activity may lower glucose significantly
• Delayed lows often happen 6–36 hours after intense or new exercise

Basal rate reductions, temp targets, and overnight monitoring prevent dips.

AID Systems and Exercise Mode

Modern AID (Automated Insulin Delivery) systems like Tandem’s Activity Mode, Omnipod’s Exercise Target, and Medtronic’s Temp Target allow users to:

• Raise target glucose (e.g., 150 mg/dL)
• Reduce basal delivery
• Reduce post-exercise lows

⏱️ Start Exercise Mode 60–120 minutes before activity.

Avoid “suspending” insulin—this increases ketone risk. Use temporary reductions instead.

What If Glucose Is Too High Before Exercise?

Although exercise usually lowers blood sugar, starting a workout with very high glucose levels can be dangerous—especially if insulin levels are low or ketones are present. In these cases, activity can further raise glucose, increase ketone production, and potentially lead to diabetic ketoacidosis (DKA).

High glucose can impair performance, decrease oxygen efficiency, and increase perceived exertion. Studies show that lung airflow can drop by up to 15% with chronically high glucose, reducing endurance and output.

✅ What to Do Instead:

1. Check for ketones

   • Use a urine or blood ketone test.

   • If ketones are moderate or large, do not exercise. Take rapid-acting insulin, hydrate well, and monitor until ketones are gone.

2. Correct high glucose with insulin

   • Use your correction factor (CorrF) to calculate an appropriate insulin dose.

   • If using an insulin pump or AID system, ensure the site works and insulin delivery is active.

3. Hydrate thoroughly

   • Dehydration falsely elevates glucose readings and impairs clearance.

   • Urine should look like lemonade, not apple juice.

4. Wait and recheck in 30–60 minutes

   • If glucose is trending down and ketones are negative or trace, light to moderate activity may be safe to resume.

   • Use CGM or frequent fingersticks to verify the trend.

By correcting high glucose before starting activity, you avoid dangerous outcomes and ensure better performance, faster recovery, and smoother glucose trends during and after exercise.

The Role of Fitness Level and Muscle Memory

Untrained muscles use more glucose initially. As muscles adapt (after 3+ sessions/week), they:

• Store more glycogen
• Stabilize glucose
• Reduce the risk of lows
• Improve performance with less insulin

Skipping workouts for 3+ days causes glycogen loss—which restarts the adaptation cycle.

Fast vs. Slow Carbs for Exercise

• Fast carbs: Glucose tabs, juice, candy, dried fruit (ideal during/after)
• Slow carbs: Oatmeal, whole grains, bars (ideal before and for longer efforts)

Sample Adjustments (Per 100 lbs Body Weight)

Your personal adjustments may vary—track and adapt.

Quick Tips for Exercising with Diabetes

✅ Check CGM before, during, and after
✅ Monitor IOB and glucose trends
✅ Start Exercise Mode early
✅ Have fast carbs ready
✅ Avoid exercising with ketones
✅ Adjust insulin based on experience and ExCarbs
✅ Stay hydrated
✅ Wear a medical ID
✅ Consult your provider if you have complications (neuropathy, eye or heart issues)

🏁 Conclusion: Be Active, Be Safe, Be Informed

Exercise is a powerful tool for diabetes management, but it requires planning, awareness, and personalization. With knowledge of ExCarbs, CGMs, insulin adjustments, and your own body, you can confidently enjoy exercising with diabetes.

Every step, lift, swim, or spin helps you live stronger and longer—with more stable blood sugars and a healthier heart.

Visit the Diabetes Exercise and Sports Association site for more information about exercising with diabetes.