Working out with diabetes can feel like a balancing act. You want to stay active (and you should—exercise is one of the best ways to improve insulin sensitivity), but there’s always that lingering question:
“What if my blood sugar drops while I’m working out?”
You’re not alone—this is a common concern among people with type 1 and type 2 diabetes. The good news? With a few smart strategies, you can exercise safely, confidently, and effectively, without the fear of hypoglycemia (low blood sugar) throwing you off track.
In this article, we’ll walk you through how to monitor your blood sugar around workouts—before, during, and after—using either a glucometer or continuous glucose monitor (CGM). We’ll also cover when to eat carbs, what symptoms to watch for, and how to fine-tune your routine over time.
🧠 Why Monitoring Around Exercise Matters
Let’s start with what happens during a workout:
When you exercise, your muscles use glucose for fuel. This can lower your blood sugar—sometimes rapidly—especially during longer or more intense sessions.
But here’s where it gets tricky:
- Aerobic exercise (like walking, jogging, or cycling) typically lowers blood sugar.
- Anaerobic exercise (like weightlifting or sprints) may raise blood sugar temporarily due to stress hormones like adrenaline.
That’s why checking your levels strategically helps you understand how your body reacts—and gives you the power to adjust before things get risky.
📋 Step-by-Step: How to Monitor Blood Sugar Around Exercise
🕒 Step 1: Check Your Blood Sugar Before You Start
When to check: 15–30 minutes before exercise.
Use your glucometer or CGM.
What you’re looking for:
- Below 100 mg/dL (5.6 mmol/L)? Eat 15–30g of fast-acting carbs (like a banana, juice, or glucose tabs).
- 100–250 mg/dL (5.6–13.9 mmol/L)? You’re good to go.
- Above 250 mg/dL (13.9 mmol/L)? Check for ketones (especially if type 1). If ketones are present, avoid exercise until levels normalize.
🔍 Pro Tip: Keep a small notebook or use an app to track how different starting numbers affect your performance and post-workout readings.
🏃 Step 2: Watch Your Levels During the Workout
If you’re using a CGM, this part is easier. Most modern CGMs (like Dexcom or FreeStyle Libre) offer real-time alerts for highs and lows.
- Set low alerts around 80 mg/dL (4.4 mmol/L)
- Set high alerts around 200–250 mg/dL (11.1–13.9 mmol/L)
No CGM? Set a timer to pause and check with a glucometer every 30–45 minutes during longer workouts, especially cardio.
Warning signs of a drop mid-workout:
- Shakiness
- Dizziness
- Fast heartbeat
- Confusion or irritability
- Sudden fatigue or sweating
What to do if it drops below 70 mg/dL (3.9 mmol/L):
- Stop exercising
- Eat 15g of fast carbs (glucose gel, small juice box)
- Wait 15 minutes and recheck
- Don’t resume until you’re above 100 mg/dL
🧊 Step 3: Check Blood Sugar After the Workout
Exercise can affect blood sugar for hours afterward—especially at night or after high-intensity sessions.
When to check:
- Immediately after finishing
- Again at 1–2 hours post-workout
- If you’re on insulin or prone to nighttime lows, check before bed and consider a light snack with carbs + protein
Why it matters:
Post-exercise lows (aka delayed hypoglycemia) can sneak up, especially if you’ve burned through glycogen stores. Keeping an eye on it helps you catch dips before they become dangerous.
🥪 When to Eat Carbs Around Exercise
Eating carbs isn’t cheating—it’s smart self-care. Here’s a quick guide:
| Situation | What to Eat |
|---|---|
| BG < 100 before exercise | 15–30g fast carbs (fruit, sports drink) |
| Long or intense session | 15g every 30–60 mins (energy gel, banana) |
| BG < 80 during workout | 15g fast carbs + pause workout |
| Post-workout low risk | Balanced snack: protein + carb (e.g., yogurt & fruit) |
💡 Tip: Keep a snack or glucose tabs with you at all times—gym bag, pocket, bike pouch, etc.
🧭 Learn Your Patterns Over Time
Every body is different. The more consistently you track, the easier it becomes to predict and prevent blood sugar swings.
Try journaling these after workouts:
- Blood sugar before/during/after
- What type of workout you did
- How long/intense it was
- What (and when) you ate
- How you felt
Over time, this becomes your personal blueprint for safe and successful workouts.
🔄 Common Questions, Answered
“Do I need to eat before every workout?”
Not always. If your blood sugar is in the 100–180 range and you’re doing a short or light workout, you may not need to eat. But always bring a backup snack.
“What if my sugar goes up during exercise?”
This can happen during high-intensity or anaerobic workouts. It’s usually temporary. If you’re above 250 mg/dL and not feeling well, pause and check for ketones.
“Is it better to work out at certain times of day?”
Many people find morning workouts more stable. But the best time is when you can do it consistently. Just be more cautious if you’re exercising late in the evening—nighttime lows are more common.
🏁 Final Thoughts: You’re in Control
Exercise is powerful medicine for diabetes—but only when it’s done safely and consistently. Monitoring your blood sugar before, during, and after workouts gives you the insight and confidence to stay active without fear.
Think of it like using a GPS—you wouldn’t drive into unknown terrain without checking the map, right? Your blood sugar readings are your map. And every workout is a step toward stronger, steadier health.
So grab your glucometer (or CGM), lace up your shoes, and go move—you’ve got this.
📌 Quick Monitoring Checklist:
- ✅ Check 15–30 mins before workout
- ✅ Watch for symptoms or drops during
- ✅ Re-check right after and a few hours later
- ✅ Eat carbs as needed to stay safe
- ✅ Track what works for your body
References:
- American Diabetes Association. (2024). Diabetes & Exercise Guidelines.
- Riddell MC, et al. (2017). “Exercise Management in Type 1 Diabetes: A Consensus Statement.” The Lancet Diabetes & Endocrinology.
- Yardley JE, et al. (2013). “Effect of exercise on postprandial glycemia in type 2 diabetes.” Medicine & Science in Sports & Exercise.
