Blood sugar levels and Workouts

Why does the sugar level spikes after workout?Is there a need to take insulin shots before workout?Pls help

Strength training workouts tend to increase BGs while aerobic exercise tends to lower BGs. This post explains in more detail:

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Hi Avinabipin,
I’ve been paying close attention to this issue. For me, it depends on the intensity of the workout. All my workouts are running.

As CatLady06 said, aerobic tends to lowers it. My BG keeps dropping as I increase my speed…up to when I get to Gray Zone 3. That’s a little faster than threshold or what some people call lactate pace. At that point my BG skyrockets!

As for why you rise AFTER exercise, a lot of this depends on the type of exercise. But generally you will be using muscle glycogen to fuel your exercise. The rise when you are finished is your liver trying to replace muscle glycogen. This is normal.

Experiment with post-workout insulin dosing to see how much you need. I always take a big dose immediately AFTER a workout, and then take in simple carbs to quickly restore what I burnt.

Check your BG during your workout to figure out the dosage timing and amounts you need. I experiment on myself everyday!

Please let me know if you want to discuss specifics and type of workout.

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Hi @avinabipin
That spike can be super frustrating right? You’ll find some types of exercise impacts your BG like this. I would have linked to an article I wrote about that but I see @CatLady06 already did that (thanks!).
I suggest you take good notes and discover which types of exercise raises your BG and if it depends on the time of day, what you’ve eaten etc. If you find a consistent pattern of higher BG then yes, you might need a shot before, during or after even if you don’t eat.
I’ve found that for most types of exercise that raises BGs it’s beneficial to eat before and after anyway, so you might just need to include a meal+insulin in your routines to solve the issue.

I had this happen to me yesterday. After my 9 mile run, my sugar was low according to my Dexcom. 20 minutes later it was 180 without having eaten anything! This doesn’t happen consistently so I don’t know what is causing it.

If you’re exercising outside this time of year, temperature may be a factor. I have a 50-minute bike ride that I do regularly, and I try to keep it up right through the winter as long as there’s no ice/snow on the ground. Under temps down to 40° F it takes my BG down about 20-30 points, depending on time of day and whether I have any lingering IOB. But somewhere in the 30s F or below it has the opposite effect. I’ve ended my ride with my BG up as much as 70 pts. It’s all about the adrenaline, or so I’m told. I think my body figures,“Hey, just gettin’ some aerobic exercise, good job buddy,” until it hits that threshold, and then the logic flips to “No sane person works this hard when it’s this cold out— he’s being chased by a BEAR!


When I workout I need to have my BG at least 150, otherwise I would go low. I usually drop around 70 points after doing 40 minutes of cardio and 10 minutes of strength training. I usually have a hard candy in my mouth while working out to avoid lows.
This is frustrating because I am having to consume carbs to avoid lows and these carbs are not helping me lose weight. Any suggestions would be approeciated. BTW I am type one for the past 40 years. I am 51, male.

This article may be of interest:


Are you on a pump? Adjusting basal prior to the workout would help. Also, having no IOB is helpful. You need to find the right range of BG and basal. With time and practice, you can get to a point where you can start at a lower BG and not drop.

Hello everyone. This is my first post on the website. I have a quick question about my sugar levels before workout. I am extremely tight with my management of sugar levels however that does not help when I work out. I try to eat something before working out to bring levels up. When I workout my sugar level crashes to the point I need to stop the activity. Any suggestions?

Many people on pumps reduce basal before working out. Those of us not on insulin have to get creative. I’ve worked out which routines raise or lower my BG and treat accordingly.

  1. For cardio which lowers my BG (cycling for 40 minutes or more; running for 20 minutes or more; looking at a pool), I use energy gels (Clif are my go-to at the moment) with a known amount of carbs at certain intervals to maintain a level BG. For cycling, I use a 25g gel at 45 minutes and then every hour after (1:45; 2:45, etc. if I go that long). That keeps me level til I’m done.

  2. For HIIT and Olympic lifting, which raises my BG, I’ve found that using Resistant Starch can help to dampen that effect significantly. I eat 30g of unmodified potato starch suspended in water about 30 minutes before working out. It doesn’t really solve the issue, but it generally reduces the rise from 70 mg/dL to 20-30 mg/dL for me.

Regardless of workout type, I tend to be a bottomless pit for carbs after working out. I usually triple the amount of carbs I’ll eat for dinner (I workout primarily in the afternoon now) in order to not stay lower than I want to (under 70 mg/dL).

All that being said, I’m a really weird case: I respond ridiculously well (BG wise) to exercise; I like to train; and I’m not yet on exogenous insulin. All of this will become far more challenging when I’m using basal insulin, although the workout-related spikes will be more easily controlled with corrections.

Are you T1 or T2?

If you are using insulin, you either have too much IOB or too much basal during your workout.

How close to mealtime are you doing your workout?

If you are using insulin, what type and how do you take it - pump or injection?