I’ve been changing my workout routine to add more Zone 2 training. Previously, I spent too much time working hard, with 3 days 4x4, 3 days Zone 3 (threshold), and 2 days devoted to strength using weights, kettlebells, and plyometrics. I’ve swapped the Zone 3 sessions for longer Zone 2 workouts, and although I am enjoying it, I am finding the hypoglycemic hit during and after hard to handle.
Recently, on a one (1) hour slow rowing erg workout, keeping it in zone, but about 45 minutes in my blood sugar dropped precipitously, even though I thought I adequately compensated with enough pre-workout sugar; it started at 230. I then grabbed two (2) glucose (maltodextrin) packets, and although that worked for a while, I had repeated lows all afternoon.
I prompted Gemini in an open-ended way, “T1 diabetic, type 1, zone 2 training, blood sugar goes low”, and it responded credibly, but I wondered about others’ experience.
I will break the hour into 2 halfs, and fuel part of the way through, but any suggestions are welcome.
Prompt
- T1 diabetic, type 1, zone 2 training, blood sugar goes low
Gemini Response
Managing blood sugar during Zone 2 training can be a delicate balancing act, as sustained aerobic exercise significantly increases glucose uptake by the muscles. Since Zone 2 relies heavily on fat oxidation but still consumes circulating glucose, the “slow burn” often leads to gradual but persistent drops.
Here are several strategies to help maintain stability during these sessions:
1. Adjusting Basal Rates
For many Type 1 athletes, the most effective way to prevent a mid-workout drop is to reduce insulin on board (IOB) before starting.
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Timed Reduction: If using an insulin pump, consider setting a Temp Basal (often a 30–50% reduction) or activating “Exercise Mode” 60 to 90 minutes before you begin. Reducing it right at the start of the workout often leaves too much active insulin in your system.
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The MDI Approach: If on multiple daily injections, some find it helpful to perform Zone 2 sessions when their background insulin is not at its peak, or they may discuss basal dose adjustments with their endocrinologist if training occurs daily at the same time.
2. The “Pre-Flight” Snack
If your blood sugar is trending flat or downward before a session, a small amount of targeted carbohydrates can create a buffer.
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Slow-Release Carbs: Foods with a lower glycemic index (like a small amount of oatmeal or an apple with peanut butter) can provide a more sustained glucose release during steady-state cardio.
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The “Safety Floor”: Aim to start Zone 2 with a slightly higher blood sugar “ceiling” than your resting target—typically around 120–150 mg/dL—to allow for the inevitable drift downward.
3. Intra-Workout Fueling
Rather than waiting for a low alert, many find success with micro-bolusing carbs throughout the session.
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Liquid Nutrition: Sipping on a sports drink or using glucose gels every 20–30 minutes can offset the glucose being burned by the muscles.
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Rule of Thumb: Start with roughly 15 grams of carbs for every 30–45 minutes of Zone 2 work and adjust based on what your Continuous Glucose Monitor (CGM) shows.
4. Monitoring Trends
The direction of the arrow on your CGM is often more important than the number itself.
- Lag Time: Remember that CGMs can have a 5–15 minute lag behind actual blood glucose levels during exercise. If you see a diagonal down arrow, it is usually time to consume fast-acting carbs immediately, even if the current reading is “in range.”
5. The Post-Exercise Effect
Zone 2 training improves insulin sensitivity for hours afterward.
- Delayed Hypoglycemia: Be mindful of the “tail” of the workout. You may need to reduce your post-workout bolus or keep a close eye on your levels 2–6 hours after finishing, as your body works to replenish glycogen stores.
