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Blood Sugar and Exercise

After 20 years of being a Type 1 diabetic the insulin has finally caught up with me and caused me massive weight gain over the last couple of years, a year of Banting did not help, it did nothing for my insulin or weight levels, so in my desperation I joined the gym at the beginning of the year.

I attend four hour long classes a week; namely Kick class, Zumba, and two spinning classes.

When I first started going to the gym I tested my sugar half an hour before class, it was spot on ranging between 4’s and 6’s, I always took a snack along with me as I expected my sugar to drop during or after exercise; as we are generally taught is the case.

To my absolute horror my sugar did not drop, the complete opposite happened, an hour after gym class I would retest my sugar levels and it would be between 15 and 22!

This is a little sample of how my sugar readings looked before and after exercise:

  • Before:  6.3  After:  16.4
  • Before:  4.7  After:  14.7
  • And the cherry on the cake, Before:  5.2.  After:  22.1.

This continued for about two months, I started to panic and was worried that I would have to stop the exercise because of this.  I thought that surely these high sugar levels after exercise were doing damage and the exercise was hurting my body more than helping it.

That was when Google became my new best friend, I googled “High Blood Sugar After Exercise” and found hundreds of articles explaining to me that the more intense the exercise is that you do, the greater the chance is that your sugar levels will spike and NOT DROP after exercise.

According to the articles I read this is due to the fact that during intense exercise your liver starts increasing the amount of glucose that it is producing, the glucose needs insulin in order for it to be used by your muscles, so if there is not enough insulin in your body at the time of exercise the glucose cannot get to your muscles and your sugar levels will spike.

I started experimenting by not snacking before class and giving a unit or two of Humalog 30 minutes before the class.  The results were epic.  Perfect levels before and perfect levels after exercise.

This is a little sample of how my sugar readings look now before and after exercise, after introducing a unit or two of Humalog before class:

  • Before:  7.1.  After:  6.6
  • Before:  6.7.  After:  7.2
  • Before:  7.4.  After 4.2.
  • Before:  7.3.  After 5.8.

Who knew!  After all these years of being taught to eat before you exercise because the exercise will probably cause a hypo.

5 months into the gyming and this regime continues, a unit or two of Humalog before class and perfect readings after exercise.

Alas, the gyming is not helping for the weight yet, but hopefully it will in time…

This is just my experience, I hope that maybe sharing my experience may help someone else suffering from the same issue.  I wish that we were taught this along with the “low blood sugar after exercise” theory.

By Frances Gates

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  1. Greg Miller Greg Miller

    Hi Frances,

    Thanks for sharing your story, I have also noticed that intense exercise raises my sugar and then the easiest exercise like a walk can drop your sugar radically I also surf and ride motorcycles and it seems that the easy but sustained activity, with a low heart rate, which is the ideal fat burning range, is also burning sugar… I have also noticed on long Adventure motorcycle trips, that the sustained high concentration burns sugar at a surprising rate.


  2. Danie Danie

    I have read Frances comment on high blood sugar levels after training. My sugar levels seems to drop during training which scares me to train at all. Example: 20min of walk and run on treadmil at low intensity. Sugar before training 13.5 and after 7.2.

    How do i maintain the perfect level during excercise. especially if i moutain bike for 40km?

  3. Jaco Cronje Jaco Cronje

    Most likely your levels rise during exercise because of adrenaline. When you exercise hard the body release adrenaline which has the opposite effect than insulin.
    The best way to track your glucose during exercise is with a CGM (continuous glucose monitor).

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