It is mostly after long bike training sessions with higher intensity efforts, running with higher intensity intervals or swim sessions with hard efforts that glucose levels tend to rise in the hours after exercise.
I established that if any of the below factors are present, levels will go up:
- More than 2.5-3 hours of bike training with reduced basal rate and with higher intensity efforts in between
- Running or swimming at higher intensity for more than 30 min or tempo/hard intervals
- A race
I found that rising blood sugar levels even occur with perfect starting and finishing glucose levels: I aim to start training with a level of 150-180 (8.3- 10 mmol/l) and finish between 70-100 mg/dl (3.9 -5.5 mmol/l).
Why blood sugar levels on the climb?
It wasn’t something that I couldn’t manage but it was actually quite hard work to get blood sugar levels down once they were up. I would of course correct elevated levels with insulin but on more than one occasion I would also have to go out for a 30min walk/ gentle jog/ cleaning my flat /car/bike - any little physical activity you can think of - to help levels to go down.
It was usually after 80-90 min after finishing training and having had some food that levels start rising to 200-250 mg/dl (11-13.9 mmol/l) and remain there for several hours despite correcting with insulin.
First I thought I hadn’t injected enough insulin for the food I had post-training (and you know what it is like, you come home exhausted and just want to eat as much as you can so miscalculating carbs is easy to do). I then decided to see what happens if I don’t have any carbs after a longer bike ride but stick to protein in form of eggs and fish only. It didn’t make a big difference!
At least I knew that my post-training meal and bolus did not cause levels to rise.
Yet, I was still not sure how to resolve this issue. It was obvious to me that my body needed insulin. The most obvious solution to this would have been to keep the insulin basal rate higher during training so that I would have more insulin. I usually reduce it to 60-70% of the normal rate when I train, which, I think, is still relatively high.
In terms of nutrition, during training or racing I only take on really what I need to avoid highs or having to inject short acting insulin. Often I don’t need more than 20-24gr carbs during a 2-3 hour ride with a basal rate between 60-70%. Increasing this rate to 80 or 90% would mean that I require much more nutrition to avoid hypos. I wasn’t convinced that this was the right solution. I had proven numerous times that my reduced basal rate and the amount of food I took on worked so decided that I wasn’t going to change my strategy during training.
Hormonal responses in the body post-exercise
My understanding, without going into too much detail as I am not a scientist, is that it is mainly the liver that is playing a major role post-exercise elevated glucose levels, so called hyperglycaemia, in type 1 Diabetics .
In both diabetic and non-diabetic people a high level of exertion (through both intensity or duration) activates the sympathetic nervous system which triggers our adrenal gland to release “stress” hormones such as adrenalin. The body’s energy expenditure is very high now and with the release of these counter-regulatory hormones, the liver receives a signal to help producing more energy. It does this by releasing glucose into the blood at a faster rate than normal. Post exercise, the effect of adrenalin continues to make the liver release glucose into the blood.
In a non-diabetic athlete after strenuous, high intensity exercise (referred to in scientific papers as >80% VO2max) the body is busy replenishing empty muscles glycogen stores with glucose using both the post-exercise food and remaining glycogen stores in the liver, which gets converted into glucose and released in large amounts to give our muscles more fuel. To be able to transport the glucose from the blood into the muscles our body requires insulin. In a healthy athlete, with rising glucose levels (whether through eating carbs or the liver releasing glucose or both) the pancreas will automatically release insulin to counteract this and as a result blood sugar values quickly return to a normal range.
Type 1 Diabetics obviously do not produce their own insulin and therefore have to think carefully about how to correct post-exercise blood sugar levels and hopefully prevent hyperglycaemia in the hours that follow.
(On a side note, it makes sense why eating carbs immediately after exercise is useful because you are actually helping your body to replenish empty muscle glycogen store and the liver doesn’t need to release as much energy in form of glucose.)
Greater insulin demands for a type 1 post-exercise?
This may not be as obvious for diabetics as it seems. Interestingly, many diabetics are often “warned” about post-exercise hypoglycemia (low blood sugar) which can occur as a result of injecting insulin after exercise in combination with muscle cells removing the sugar from the blood to restock glycogen and your body being more sensitive to insulin. However, I have only very rarely experienced low sugar levels or an increased insulin sensitivity (not even after my Ironman). I can however confirm that once I have managed to maintain stable sugar levels in the first 1-3 hours post-exercise, levels are usually pretty good for the rest of the day and no insulin resistance occurs.
There is loads of interesting research on exercise metabolism and glycemic control and I am only scraping the surface of a highly interesting process of the human body in post-training state.
Understand your body?
I am glad my perseverance paid off. I just didn’t want to accept that elevated levels after higher intensity sessions were part of training with diabetes. I am also glad I had enough courage to up my temporary basal rate by 30% more immediately after training for 3-4 hours. It was something that felt extremely counterintuitive when finishing a training ride or race with a level of 70-80mg/dl (3.9-4.4 mmol/l) and in the back of your mind you hear the medical professionals telling you about the danger of a hypo after exercising due to increased insulin sensitivity.
It is worth the risk sometimes doing what seems to be at odds with what is “normal” .This is not just true for managing Diabetes.