If you regularly do cardio (like running, swimming, dancing etc.), you have probably noticed that your blood sugar reacts differently depending on the type of cardio. While steady-state cardio will usually make your blood sugar drop, interval training can make it increase (you can read why in this post).
The same goes for resistance training (weight lifting) and blood sugar. Some types of resistance training will make your blood sugars increase!
In this post, I’ll talk about how different types of resistance training affects your blood sugar and the strategies you can try to proactively manage your blood sugar during and after resistance training.
I absolutely love resistance training for three simple reasons:
- Resistance training makes me feel strong and empowered.
- Resistance training has helped me shape my body to my liking.
- Resistance training ultimately makes my diabetes easier to manage, as it improves my body’s ability to utilize insulin.
Resistance training generally falls into two categories
- Low-rep (heavy) training with pauses between each set.
- High-rep training or supersets with little rest between sets. Your heart rate is elevated throughout the workout.
Each type of resistance training will affect my blood sugar a little differently during my workouts but they both have the same long-term benefit of a significantly improved insulin sensitivity.
How high-rep resistance workouts affect my blood sugar
In general, I need to be a little more careful and watch my sugars more closely if I do high rep workouts, supersets, or a lot of compound leg exercises (like squats, deadlifts, or lunges). These kinds of workouts will have a cardio-like (aerobic) impact on my blood sugar since my heart rate will be elevated for most of the session and I can expect my blood sugars to drop.
I treat sessions like these almost as I would treat steady-state cardio – by reducing my pre-workout bolus by about 30%-50%.
How low-rep resistance workouts affect my blood sugar
When it comes to more traditional resistance training with fewer reps (less than about 12 reps per set), the situation is a little different. When doing workouts like this, I sometimes see my blood sugar go up, and sometimes I don’t see much of an impact at all. It basically comes down to what body part I’m training.
For smaller muscle groups like arms and shoulders, my heart rate won’t usually increase that much despite the heavy weight, and my blood sugar will remain stable. If I do heavy chest, back, or leg workouts, however, I’ll most likely see an impact, and it can often be an increase. My body reacts in the same way as when I do an interval cardio workout.
Given this knowledge, I’ll reduce my pre-workout bolus minimally or not at all for a low-rep workout, depending on the body parts I am training.
How to prepare for resistance training and prevent post-workout lows
When it comes to resistance training, pre-workout meals play a huge role in whether you’ll be successful in the gym. I always eat something before and after a strength-training workout to make sure I have enough energy to do the workout, to rebuild my muscles, and to maintain good blood sugar levels.
My pre-workout snack is a fairly low glycemic carb (like brown rice) and some lean protein (like chicken breast) which I eat about an hour before my workout. By eating a low glycemic carb plus some protein, I get enough energy for my workout without having to take a lot of insulin.
My post-workout snack consists of a low or high glycemic carb with an easily digested protein (like fruit and a whey protein shake).
As mentioned, I generally reduce my bolus amount for the pre- and post-workout meals by up to 50%, especially on high-rep and superset days, due to the cardiovascular (aerobic) component of the workout, which always makes my blood sugar drop. However, taking a bit of insulin before a resistance training workout also has the benefit that it reduces my risk of high blood sugar during the low-rep sessions.
How to adjust your insulin up to 36 hours after a resistance workout
My approach to insulin adjustments for the 24 to 36 hours after I leave the gym is the same no matter what kind of resistance training I’ve done. What happens when you do resistance training is that you create microscopic tears in your muscle fibers, and for the next 24 to 36 hours, your muscles heal and get bigger and stronger. During this period, your muscles need energy in order to heal and that has to come from somewhere, so low blood sugars can easily be the result if I don’t plan ahead.
If I do resistance training less than four times per week, I will typically have to reduce my nighttime basal insulin by up to 50% on the days on which I work out (this is different for every individual, so you need to experiment and track your results to find what works best for you).
If I do resistance training more than four times per week, the increased insulin sensitivity is present all the time and I can simply lower my nighttime basal permanently without having to adjust for individual workouts.
Summary
I find it easier to adjust for resistance training than for cardio, as long as I am very aware of the kind of resistance training I am doing and remember these guidelines:
- High-rep workouts in which your heart rate is elevated will most likely make your blood sugar drop.
- Low-rep workouts that don’t elevate your heart rate significantly (like arms or shoulders) most likely won’t affect your blood sugar.
- Hard low-rep workouts of large muscle groups can affect your blood sugar like an interval workout, potentially leading to an increase in blood sugar.
- Don’t be scared of eating!!! Eat enough lean protein and carbs to fuel your workout, ensure muscle recovery, and (with the appropriate insulin dose) stabilize your blood sugar levels.
- Consider reducing your insulin levels appropriately during the 24 to 36 hours after a workout to adjust for the type of resistance training you’ve done.
Have fun in the gym!
Suggested next post: How to Prevent Low Blood Sugar during Cardio Workouts
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Thanks for this blog. I’m navigating new waters and looking for all the info I can get. I was diagnosed with T1D at age 41. I won’t go on about my symptoms leading to diagnosis, but I’d been sliding into it for at least a year. Pertinent to this post, I happened to exercise obsessively daily at the gym during my age 40 year, and it’s likely that saved my life, lowering my blood sugar levels just enough. My blood sugar levels (daily and H1AC) were the highest my diagnosing doctor said he’d ever seen, at over 26 mmol/L. I’m an American living in Finland, BTW, so I express blood sugar values in mmol/L.
I’m curious about how to time insulin best to make muscle gains. It seems that for muscle to obtain energy, you’d need to shoot insulin a bit before the workout. I try to take in 2 units after I’ve had a pre-workout meal. and go into the gym at around 10 – 12, and usually leave at a healthy 5-8 depending on what I do (like you said, high rep and leg day can drop BS more dramatically). I’m told to keep my levels between roughly 4.6 – 10.
Question is: does pre-workout insulin matter for gains? Seems it must, but just want to make sure. Before I got on insulin, I lived in a perpetual state of leg cramps for one year, as I lost weight dramatically (230 lbs to 165, I’m 6-4), and my leg muscles withered worse than my upper body for some reason. Running and leg workouts were excruciating, and I could never maintain much less gain muscle on the legs, but I’d push through anyway. Where everything felt bad last year, it all feels pretty good this year. I don’t “feel” a difference between taking or not taking insulin pre-workout or after a post-workout recovery meal/shake, but I’ve put on muscle (and some healthy fat) this year dramatically (back to around 200 lbs). No clue if timing insulin dose has an effect on muscle gain.
Hi, glad you got diagnosed! That sounds like a scary situation.
For muscle growth you need to manage your BG (which you are), eat enough and lift heavy. Reason, why you lost muscle, is most likely that your body was starving and eating away at your muscle mass.
Your current strategy of eating and dosing prior to your workout sounds spot on, ending at 5-8 is pretty darn good. I’d just continue down that road and push through. If you find you don’t put on mass try increasing your calories and change up your workout.
Always helpful tips – thank you. One question. When you say: “I treat sessions like these almost as I would treat steady-state cardio – by reducing my pre-workout bolus by about 30%-50%.”. As a pump user, would that equate to reducing my basal by that much?
Hi Libby,
If 30-50% basal reduction is what works for you for cardio you could definitely try that out for high rep sessions. If you eat before you could also try only to reduce your bolus or omit it completely (depending on the size of the meal of course). I think you might find that your formula for cardio won’t fit 100% so you probably have to do small tweaks.
Thank you so much for the insight!!! You absolutely ROCK! My question is, do I withhold carbs (all) until I get my numbers where they need to be or do I follow the meal plan and let my levels adjust on its own? I’ve started cardio more frequently but I love weight lifting and I’m afraid to lift because of spikes. Will cardio after lifting be the way to go or is that too much stress?
If you use insulin I’d suggest you manipulate your IOB (insulin on board) to take care of spikes. You can try walking after, often that will help your blood sugars come down after (that also works if not on insulin).
Generally, I’d suggest eating at least a little before a resistance training workout. If fasting many see the spike increase.
And thank you 🙂
Hi Christel,
I have a question regarding carb tolerance and the beneficial effects of building muscle. For example, suppose someone has a BMR of 1500 and is somewhat active with a TDEE of 2250. Let’s assume that this person can eat a maximum of about 200g of carbs (from a combination of high and low GI sources) a day for good daily blood sugar control and favorable triglyceride, A1C, etc. markers.
Now suppose this person builds about 4 pounds of muscle with 4 pounds of fat. Since a pound of muscle burns ~6 calories at rest and fat ~2, that would push the BMR to ~1530 with a TDEE around 2300.
Do you think it sounds reasonable that the daily protein requirement might increase by roughly 2-3 grams (so about 10 of the extra 50 calories)? If that is the case, that would mean about 40 extra calories for fat and carbs. Is it fair to say that this could be split about equally? So in this case, with 20 calories leftover for carbs, that means this person would have their carb tolerance increased by only about 5g a day? Just wondering if this is a somewhat accurately way of looking at the situation or if it’s more complicated than this.
I know the situation changes if other factors such as carb sources and stress are put into the mix, but in this scenario it would be assuming all of these other factors remain the same. I was also thinking that it could be hard to tell since resistance training can increase insulin sensitivity without gaining much actual muscle. So I guess it also comes down to how much actual glycogen storage is available.
Thanks,
Jason
I’m not sure. Generally, I’d say that 40 calories / 5 g of carbs are so small numbers that they aren’t worth spending a lot of time thinking about.
And other factors play in as well like glycogen storage, hormones, eating schedule etc. so basically I don’t think I can give you a meaningful answer
Christel,
I recently found your website and have been binge-reading all of your articles about how to control your blood sugar during workouts and how to tweak your pump settings for different kinds of workouts. This information is gold and I am so glad I found your site! One thing I did notice though that I don’t think you have mentioned, is what do you do with your pump during the actual workout? You mention that you reduce your pre-workout bolus and basal rates sometimes, but what do you do during the workout? Do you keep your baseline basal rate going? Do you unplug your pump?
Hi Kayla, so glad that you find the site useful!
I’m sure you already have read the article on insulin adjustments using an insulin pump, but if not I think you’ll find it helpful (HERE).
What to do with the pump depends on how much of a reduction you need (or if you need more insulin of course). If you only need a basal reduction during your workout you’ll have to keep your pump on. If you need to do a suspension during your workout to not go low you can, of course, take it off. In general, it’s not recommended to go more than 60 min without any insulin delivery.
Start slow and do a structured experiment to find if you need to reduce or suspend during exercise. I highly recommend following the guidelines (I’ve tried to make them easy to follow in the article in the link above) and figuring out what works for you. And always bring your emergency snacks!
Dear, Christel,
I have diabetes since last 11 years. 1 month back my doctor has diagnosed that I am Type1 Diabetic. He told me to take 3 shot of human Actrapid insulin for breakfast, lunch & dinner respectively and one shot of Basalog insulin in a day. But I kept taking only insulin once in a day. No human Actrapid. It way OK. I was a bodybuilder 10 years back. I never stopped workout. After a while I started workout again. But to my surprise I found that, while doing workout my sugar level keeps dropping but after 24 hours as workout pain starts, my sugar level shoots up to above 300.
I had already reduced my Basalog insulin UpTo 2 unit (100IU=1ml) I was about to get rid of insulin. But now the whole picture is different.
Please guide me.
Thanks & Regards
Rakesh More
If you have Type 1 diabetes you have to take insulin. There’s no way around it, no amount of exercise can eliminate your need for insulin. I’d suggest you go back to your doctor and discuss the situation with him. However, if you want to do it on your own you’ll need to determine how much to lower your insulin so you don’t go low during exercise and how much to increase it to not go high after. It might be a question of lowering your basal as you have done and adding a small bolus after
My A1C level 3 months ago was 10. I applied for a part time job at Fedex as package handler . I started unloading trailers for six hours ,five days a week. Today my doctor told me that my A1c dropped by 3 points.I have decided to eat no carb and NOmeat on my way to sleep every night . Hope to drop by another point .Thank you FEDEX.
Sweet!
Went for a walk 23 min lifted 3 sets of 10 on my legs and ate oatmeal for break fast.
My sugars 134 upon weakening then jumped To 214 at lunch time check. So confused
Different things could be going on. It could be a one-off, but if you see it consistently you’ll have to develop a strategy for that. If you’re on insulin and reduced that before/during exercise you might need a little extra after. Could be the anaerobic exercise impact (as you read in the article), messy infusion site/injection etc. I suggest you track your BGs for a while and see if this is a reoccurring theme
Since I work a real physical job every day, not living in a gym, I have no major sugar problem like you are saying I should have…? Should I continue doing what I am doing or should I be concerned?
Seth, I’m not sure what you’re asking. If your blood sugars are within range all the time you’re obviously very good at managing them and I don’t see any reason to make changes. All the posts on the website are meant as support but if you don’t need it, that’s not a bad thing
I workout early morning before work and need most days to take a unit or 2 bolus as hormones makes my blood glucose levels rise, I don’t eat breakfast during the week and this works for me.
I’ve been reading a lot lately on how BCAA’s can help with getting your protein intake and can help with insulin sensitivity. Is there any proof of that or have you experienced yourself any of those benefits?
There is a lot of conflicting opinions out there about BCAAs (and the science isn’t conclusive yet) but I belong to the school who think that they don’t make any real difference as long as you otherwise eat a healthy balanced diet. Especially, I have never seen convincing evidence of their effect on insulin sensitivity. But they won’t hurt you, so you can try them for a while to see if they do something for you if you like.
Christel, thank you for the thorough article. I loved your explanation about the mini muscle tears after an intense strength training workout that calls for a decreased nighttime basal up to 50%. Your insight is very helpful to me and many many other T1Ds. Thank you.
Thank you for the feedback, I’m so glad it’s helpful!
Christel,
I have Type 2 diabetes and take oral medication once a day. How do I figure out what types of exercise lower my bs and should eat the same combination of pre and post workout meals as you suggested?
Hi Laura – that great questions.
In general, exercise impacts us the same way. So if you’re looking to lower your BG now cardio is the way to go. Resistance training can improve your insulin sensitivity in the long run, so that’s more of a long term investment.
I would still include a small snack before a resistance training. You can start with a lean protein and small serving of carb (maybe 1-2 rice cakes) and see how it goes. If that doesn’t work for your blood sugars you can consider cutting back on the carbs
Would you please explain what you mean in Summary Item #4, where you state that you should eat enough carbs to “combat exercise-induced high blood sugar levels.” I don’t understand how eating carbs would combat high BG. Or did you mean to say that carbs would combat exercise induced low blood sugar levels?
Hi Susan,
Thank you, that was not well written. I’ve changed it, so hopefully, it makes more sense now. In this specific context, I was referring to the overall benefits of fueling your workouts, adding that the right combination of food and insulin additionally is a way to reduce the risk of highs or lows.
You have no idea how helpful this article and these daily challenges have been for me. I dont know any other type 1 diabetics and finding this information has seriously taken so much anxiety away from me from feeling like im alone. Thank you 🙂
Carly, you are welcome – I’m so glad this is helpful to you!!
I always believed that armed with the right information we can be successful, in pretty much anything. The more we know about what’s going on with our bodies (hopefully) the less anxious we become.
Keep soldiering on