Zone 2 Training and Hypoglycemia

T1D Tech & Daily Management Support
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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.

  • 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.

  • 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.

  • 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.

  • 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.

  • Liquid Nutrition: Sipping on a sports drink or using glucose gels every 20–30 minutes can offset the glucose being burned by the muscles.

  • 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.
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Hi. Welcome to the forum. Do you pump or MDI? If you pump what basal reduction did you try (starting at 230 with a high basal rate and i can be 50 mg/dl in an hour). If you MDI, what did you do for your long acting on the day of your workout?

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I take Tresiba in in the AM, 24 units

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@james.j.igoe Well, that’s what’s killing your blood sugar. It’s really hard to do endurance exercise if you took long acting (more than 50% of your normal long acting). And if you matched your long acting to your 1-2 hours of endurance exercise, you will be chasing highs. One of the big reasons I use a pump is I can temporarily turn off basal. I can turn it down or completely off and if I start reducing basal at the right time I won’t crash. :peace_symbol::shamrock:

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I use MDI, and the Tresiba was my normal AM dose. I have considered a pump, but never switched.

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@james.j.igoe Tresiba is even harder to vary for occasional exercise because it usually takes 3 days to reach steady state. If you work out often you might be able to just reduce your Tresiba dose, but I recommend you talk to a doctor if you are uncomfortable making changes yourself. There is no right answer here because if you are not trying to lose weight, you can be successful with just carb load (try for example carbs and protein) before, during, and after exercise.

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If I were to look into pumps, any suggestions? My fitness activities are rowing and ski ergs, spin cycling, weight training, kettlebells and plyometrics. GeminiAI gave me some suggestions, and then filtered it down to the OmniPod and the Tandem Mobi. Any thoughts?

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@james.j.igoe I think they are all good but I like Tandem, really because Tandem uses Dexcom CGM (Libre too) since Dexcom works really good for me picking a pump that integrates with Dexcom was a critical component. All the new pumps including Tandem, omnipod, beta bionic, and Medtronic, uses the CGM signal to increase and decrease insulin delivery. If you use a CGM now and like the one you are on, pick from the pumps that integrate with it. So I am using the Tandem Mobi it’s a very small tube pump and it works well managing days like today (sitting by a computer) and field days where I am working in construction sites. It allows me to do intense exercise but I do have to manually stop basal because the pump control algorithm isn’t fast enough for very big changes in my activity.

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This is a very comprehensive and good outline, James @james.j.igoe , and welcome to the Breakthrough Community Forum!

What you presented can be used by many people for managing day-to-day diabetes, not only for those on heavy training regimens. Your advice for those using a pump to reduce basal rates 60 to 90 minutes before exercise can be key in avoiding hypoglycemia - “total active” insulin on-board is quite different from “bolus” on-board which many pumps label as “insulin on board”.

From my experience with pumps [now with my 5th pump] and MDI [I joined a team in 1985 developing MDI protocol] I find a pump to be much easier managing almost every activity type.

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James! I’m so glad you’re giving the BT1D forum a try.

I experience something similar with my 5 mile walks, I can maintain a steady state for 45 minutes and then there will be a drop that requires carbs. My solution at the time was to move the walk to before breakfast so I had only basal insulin on board. Personally I needed a couple of units to deal with the usual morning rise and that supplied my muscles energy needs nicely. Try looking for solutions in your meals and the associated bolus(es) before your workout.

Another thing to try, if it doesn’t ruin your workout plan, if your glucose starts dropping try sprinting for 10-30 seconds. Did you ever see a rise after competitions?

I just started on a pump and tried hiking with a group of T1Ds. My blood sugar was mostly fine, like Joe said, I dialed in a temp basal rate on the drive over, easy peasy. Forgetting sunscreen and too much time in front of the computer were problems the pump couldn’t solve.

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I do experience a glucose drop after about 1 to 1.5 hours walking, but I usually have sent my sugar a bit high beforehand, as well as walk intensely, even though it is my casual walk.

Although I do get sugar risng during or after intense interval workouts, my feeling is that a short sprint wouldn’t provide me a boost, although I will do some research to see if is plausible.

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I went digging for the sprint raises BG reference and finally found it was a question of the day on T1D Exchange.

While exercising, have you tried a 10-second sprint to raise your glucose level? Share your tips and tricks to raise your glucose level during exercise.

I apologize for getting the duration wrong. There must have been enough positive responses that I gave it a try.

While digging I did find this interview that may have some useful info:

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Hey @spdif , no worries about the time inaccuracy, but thanks for the great article! It’s chock full of good information.

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I have used these sites before, and generally post to several sites simultaneously. Since I am more information-oriented than looking for social connection, I opted for the same post in both the T1Diabetes and BreakthroughT1D forums.

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Years ago, I discussed a pump with an endo and stated that “I wouldn’t want to use it unless it is tubeless.” That time is here. Both the Tandem Mobi and OmniPod have comparable performance, so it comes down to lifestyle factors, mobility, exercise, ease of use, waterproof-ness, etc. For now, I’ve asked my endo about the devices, stating a preference for the OmniPod, but looking for her opinion. She’s great about both technical details as well as talking, and getting feedback, from her patients.

GeminiAI Summary

Prompt: Are there any studies or user information to see which provides a better experience or control?

Response:

The consensus from these studies is that both systems provide exceptional, statistically comparable glycemic control.

Here is what the data and user experience reports indicate:

  • Time in Range (TIR): Multiple retrospective studies analyzing patients who switched from multiple daily injections or manual pumps to these automated systems show near-identical improvements. Both the Omnipod 5 and Tandem Control-IQ consistently increase a user’s Time in Range by 10 to 15 percentage points on average within the first 90 days of use, while drastically reducing the risk of severe hypoglycemia.

  • Algorithm Differences: While the end results are similar, the algorithms get there differently. Tandem’s Control-IQ uses a “treat-to-range” strategy, aggressively adjusting basal rates and giving automatic correction boluses to keep you between 112.5 and 160 mg/dL. Omnipod 5 uses a “treat-to-target” strategy, adjusting micro-boluses every 5 minutes to gently steer your glucose toward a customizable target (e.g., 110 mg/dL).

  • User Experience & Burden: Because the glycemic outcomes are so similar, studies note that patient satisfaction comes down to lifestyle and hardware preferences rather than algorithm superiority:

    • Waterproof vs. Water-Resistant: The Omnipod 5 pod is fully waterproof up to 25 feet for an hour, meaning users can swim and shower without interrupting their automated insulin delivery. The Tandem Mobi is water-resistant, but users are advised to physically disconnect the pump and tubing before swimming, which stops automated delivery during that time.

    • Wearability: Omnipod users report high satisfaction with the freedom of having no tubes, but sometimes report frustration with the bulkier profile on the skin and the fact that a pod cannot be temporarily removed (if you take it off, it must be thrown away). Tandem Mobi users appreciate the ultra-small footprint and the ability to temporarily unclip the pump to change clothes, but still have to manage the physical tubing.

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I hope no one minds, but I had Gemini summarize the article. I appreciate the format Gemini writes in, as it is similar to a style I use for information, work, and reports.

Summary:

The article from T1D Exchange is an interview with Sam Scott, PhD, CEO and co-founder of Enhance-d and co-author of the book “Empowered: The Science of Exercise with Type 1 Diabetes.” The article discusses how different types of physical activity impact blood glucose levels and outlines strategies for individuals with type 1 diabetes (T1D) to safely manage their workouts.

Here is a summary of the core scientific insights and advice shared in the interview:

1. Fasted Exercise (Morning Workouts)

  • How it works: Doing exercise first thing in the morning before breakfast means there is less insulin on board (IOB) from a prior bolus meal.

  • Benefits: * Lowering insulin on board reduces the risk of muscle contractions causing sudden hypoglycemia (low blood sugar), creating more stable glucose levels during the session.

    • For athletes, it can elicit a greater training effect by triggering specific metabolic pathways at a molecular level and encouraging the body to burn fat instead of carbohydrates (useful for weight management).

  • Downsides: Without active carbohydrates to burn, it is harder to sustain high-intensity or very long-duration workouts.

2. The Impact of Exercise Order and Type

Different workouts trigger distinct hormonal and metabolic responses:

  • Cardio / Aerobic Exercise: Lower to moderate-intensity workouts (like jogging or cycling) typically cause blood glucose levels to decrease.

  • Resistance / Anaerobic Exercise: High-intensity, high-energy resistance training (like heavy squats or deadlifts) and sprinting often cause blood glucose to rise.

  • The Physiology: Intense exertion triggers the release of stress hormones like adrenaline, which signals the liver to dump stored glucose into the bloodstream.

  • Practical Application: Knowing this allows individuals to use exercise choice as an “extra tool” to manipulate glucose levels rather than always having to adjust insulin doses or eat extra carbohydrates.

3. Fueling and Sports Nutrition Complexities

  • The “Two-Sided” Challenge: Fueling with T1D requires balancing the energy required for the physical work itself while simultaneously managing a safe blood glucose target range.

  • Under-fueling Risk: Because individuals with T1D are highly focused on avoiding hyperglycemia, they often under-fuel, which can hurt athletic performance.

  • Carbohydrate Absorption: Commercial sports supplements are frequently formulated with a 2:1 ratio of glucose to fructose to maximize carbohydrate absorption for endurance athletes. However, people with T1D must understand how these different sugars metabolize differently to manage their glucose correctly.

  • Post-Exercise Recovery: Refueling properly during specific post-exercise windows is crucial, as the body’s mechanism for replenishing muscle glycogen relies heavily on insulin. Missing these windows can hinder overall sports recovery.

4. Tips for Approaching Exercise Confidently

  • Data and Planning: Look closely at historical glucose data to see what works best. Try to form a plan 1 to 2 hours before a workout to reach a comfortable blood glucose target and ideal insulin on board level.

  • Glucose Target: While a common starting target before an exercise session is around 7 mmol/L (126 mg/dL), this should be individualized based on whether the session is recreational or competitive, as well as the intensity of the workout.

Source Article

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@james.j.igoe What so called artificial intelligence CANNOT tell you is how you will react. Bad news bruh, not everyone can raise their blood sugar by doing anaerobic exercise such as weight training. I crash, miserably, with high basal, iob, any amount of insulin with both cardio and with weights. How did I know this before Gemini was born? Well by trial and error and the law of small numbers. You can’t replace real world experience with a large language model bot, no disrespect, I use copilot to do my end of year summaries and it’s great for that. :peace_symbol::shamrock:

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Obviously, you’re making some assumptions about how I think, but using a large language model to summarize material simply makes it easier digest. It doesn’t negate personal experience, or whatever one uses to make decisions.

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…and if you read the summary, it doesn’t say that everyone has the same response.

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Oh I’m sorry I was exaggerating and trying to be funny. No offense at all i actually use ai to help find sources of data (like citations, legal basis for building codes, etc) but i do like to make fun of it because of “knowledgeable dumbness” of it at times. Not intending to imply anything, especially with regards to how you think. I hope I didn’t cause any trouble. I do really want to know what you are planning to do (reduce your long acting, try a pump, other) and I want to know how it works out for you.