If you’re a marathon runner or triathlete with diabetes, you’ve probably experienced the dreaded post-exercise low — sometimes hours after you’re home and showered. These delayed crashes can feel unpredictable, but the truth is: they are predictable once you understand the physiology.
Let’s break down why they happen and exactly how to prevent them.
Why Do Blood Sugars Drop After Long or Hard Workouts?
1. Increased insulin sensitivity
Your muscles act like sponges for glucose up to 8 hours after long or intense exercise.
2. Glycogen depletion
When your muscles run out of stored carbs, they aggressively pull glucose in to refill.
3. Too little post-workout carbs
Skipping recovery carbs is one of the top causes of delayed lows.
4. Too much insulin on board
Especially if you ate close to the workout or corrected highs before training. Or maybe you’re on a pump and you forgot to switch into activity or exercise mode before starting training.
Workouts Most Likely to Cause Post-Exercise Lows
- Long runs
- Long bike rides
- Zone 2 endurance
- Brick sessions
- Tempo + threshold workouts
- Swim + bike combos
High-intensity intervals can spike blood sugar during the workout — but still cause lows 2–6 hours later.
How to Prevent Post-Workout Lows
1. Eat recovery carbs within 30 minutes!
- Chocolate milk
- Rice + meat/tofu/fish
- Smoothie with banana + protein
- Greek yogurt + fruit
2. Pair carbs with protein
Protein slows digestion = steadier glucose curve.
3. Avoid correcting post-exercise highs instantly
Wait 20–30 minutes to see if adrenaline resolves the spike.
4. Fuel during long workouts consistently
Aim for 60-90g carbs/hour, depending on the event you’re training for! Many have to work up to this and train the gut. Start at 15-30g carb/hour during your base training and work up to this!
5. Avoid training completely fasted
Fasted training is the #1 cause of early and delayed lows. Fasted training is never a good idea!
Nighttime Lows After Afternoon Workouts
This is common for endurance athletes.
Strategies:
- Add a bedtime snack with carbs + protein
- Avoid aggressive dinner corrections
- Choose balanced meals (protein + carbs + fat)
- Avoid late fasted training sessions
Make sure it’s not a compression low – we’ll talk about this during our CGM review!
Conclusion
Post-exercise lows don’t mean you’re doing anything wrong — they mean your body is trained and responsive. With the right fueling strategy, you can prevent delayed crashes and recover more effectively, allowing for stronger performance the next day.
Ready for stable energy, predictable blood sugars, and faster race times?
I help endurance athletes with diabetes master fueling so they stop guessing and finally perform consistently. There are a million reasons runners and triathletes bonk during races, don’t let your blood sugars be one of them!
Book your 1:1 Endurance Fueling Consultation with Courtney now.
Grab my Top 10 Snacks for Pre-and Post-Workouts to Avoid Lows!
Want more tips? Follow along on Instagram.
More information from the American Diabetes Association, here.
