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I've edited this so it hopefully meets the guidelines of this forum.

I'd like to know if there are any studies that demonstrate an anticipatory effect similar to classical conditioning, increasing glucose levels prior to exercise.

For instance, is there any evidence that fasting blood glucose can be modified by a habit of early morning exercise? According to the Mayo Clinic optimal fasting blood glucose should be < 100 mg/dl, but blood glucose should be > 100 mg/dl before undertaking intense exercise.

Are there any studies that indicate your body "learn" to manipulate its glucose level in anticipation of exercise?

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    Joseph, by saying "your body learn to manipulate its glucose level in anticipation of exercise" do you mean this as an entirely psychological process? So, like I plan to have an exercise in 1 hour and just thinking about it would increase my glucose levels. Glucose level certainly increase during psychological stress and can increase when you are in "fight" (vs "flight") mode. So, convincing yourself into a fight mode before exercise could increase your glucose level. – Jan Aug 7 '19 at 7:34
  • That sounds like an interesting hypothesis @Jan. Can you find any studies supporting that? – Chris Rogers Aug 7 '19 at 7:39
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    @ChrisRogers, I've seen you've answered the question. I think the OP asks if you can increase blood glucose levels before exercise "just by thinking about it." I'm pretty sure this is explained somewhere as part of "sports psychology" and I was thinking if you can come up with something related. – Jan Aug 7 '19 at 7:42
  • @Jan - Hopefully my edit will help on that – Chris Rogers Aug 7 '19 at 8:38
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I have not found any studies carried out regarding a classical conditioning to increase blood glucose before exercise.

However, if you do not have enough insulin available, due to diabetes for example, blood glucose levels sometimes actually go up during and after physical activity, causing the levels to be too high (hyperglycemia).

Exercise can trigger the body to release stress hormones, like adrenaline and cortisol. Adrenaline can stimulate the liver and the adrenal glands to release glucose and cortisol which makes you more resistant to insulin. Strenuous activity, like competitive sports, can trigger even more stress hormones, in which case blood glucose usually increases.

Basically, stimulated by the demand from your exercising muscles, your body is pouring glucose into your bloodstream.

On the flip side, diabetic people also need to be wary of hypos. Low blood sugar, hypoglycemia, can occur during or after exercise when the body has used a high level of its stored sugar (glycogen).

People taking glucose lowering medications should be aware of the risk of hypoglycemia that sport can present. Sport can cause the body to be more sensitive to insulin for up to 48 hours after exercising and people on insulin may need to take this account, particularly when next going to sleep after exercise to avoid hypos during the night (source: Diabetes UK).

This is why diabetic people need to constantly monitor their blood glucose levels before, during and after exercise.

Let's look at the hypothesis you put forward. Unless you eat a high sugar food before exercise, what would cause your levels to rise?

@Jan in the comments puts forward a good hypothesis that activating the fight/flight response could increase your blood glucose levels in the same way exercise can.

Remember that an increase in adrenaline can stimulate the liver and the adrenal glands to release glucose and cortisol. If you activate your fight/flight response, you can therefore increase blood glucose levels. This is in order for the muscles to have enough energy for you to flee from danger.

This also highlights further problems for diabetic people to be wary of when under extended periods of stress and anxiety.

If you look at this question and answer from Psychology & Neuroscience, you can see that watching a horror movie can activate your fight/flight response, so can remembering a scene from a horror movie, replaying it in your head. You may need to be cautious using the fight/flight response regularly though.

Over the years, researchers have learned not only how and why these reactions occur, but have also gained insight into the long-term effects chronic stress has on physical and psychological health. Over time, repeated activation of the stress response takes a toll on the body. Research suggests that chronic stress contributes to high blood pressure, promotes the formation of artery-clogging deposits, and causes brain changes that may contribute to anxiety, depression, and addiction (source: Harvard Medical School).

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  • Thanks, Chris. I suspect, as you do, that this is possible, but was looking for experimental verification. I've followed a whole-food, plant-based diet, which is quite rigorous, for about four years. I also do the Grouse Grind (bit.ly/2Z0HBJR - I live on Grouse Mountain), which is an 853m climb before my workday, before I have breakfast. And, I've got a 25 BMI. So, I was extremely surprised the other day when I measured my glucose levels after putting on my climbing shoes and noticed it was a high at 5.6 mmol, compared with my last lab test: at 4.8, which prompted this hypothesis. – Joseph Aug 13 '19 at 20:43

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