Right, I said I'd respond to this and I've finally got to it.
Firstly, I can really understand where you're coming from. I've not been diagnosaed anywhere near as long as you, but I was also very athletic at the time of diagnosis aged 39, being just 8 weeks away from an ultramarathon so building up to the peak of training (knee went out on me at 40 miles, but BG control was good by the way).
In the last 2-ish years, it's really taken a lot of experiementing and learning by both failure and success to get to the point where I am now.
Recommendations above for Pumping Insulin and also Think Like a Pancreas are both good starting points for the theory, I'd also look online as there are lots of papers published as well which would help.
Coming back to the start, and the functions of insulin and how it acts during exercise
1) Glucose transport to muscles
2) it's a fat storage hormone for excess sugar
3) supresses utilisation of fat in the presence of available glucose.
Practically what this means is getting the basal right to start with so that you are not needing excess carbs to deal with an excess of insulin that then gets laid down as fat, or supressing your ability to utilise fat as fuel. Both books give some pretty good guidance on basal testing, or just come back and ask here.
During exercise two things happen, your body becomes more inslin sensitive and also GLU4 receptor starts to become more active as a non-insulin glucose transprt mechanism. In normal people, the pancreas would react to the exercise and reduce it's insulin output to almost zero over the space of 30-60 mins. You and I can't do that so easily, we're limited to the dose we've already put on board wither via basal, bolus or pump rate.
What we've then got to take into account is counter regulatory hormones as well, cortisol and adrenaline for example which stimulate the liver to release glycogen for the fight or flight reaction, typically in response to short, sharp efforts or going out harder than usual on endurance work and getting the HR tooo high.
For steady endurance work therfore, where the stress hormones don't come into it, the key is reduction in bolus and/or basal rates to prevent huge drops in BG that you can't control. This means testing regularly and "eat to the meter".
My general strategy is that for an easy hour or so on the bike or running etc, I need to drop the basal rate to 30% of normal about 3 hours before the planned run, Test before going out and if <5.5 eat a smalll snack. Take meter and carbs with me and test every 4-5km on the run, every 30-45 min on the bike, aiming to keep BG between 5 and 7. I'm typically needing about 20-25g for an hour. These will usually be evenings.
For a longer run or ride, tyically the Sunday morning job, it's a bit different. The basal gets turned down to 20% on waking, breakfast is moderate carbs but with bolus reduce by 2/3 so fo a bowl of porridge, isntead of 1.2U it might be 0.3-0.4U. This seems to take care of the later insulin sensitivity, but not letting BG get too high before I set out. Then it's the same again, test regularly and eat to the meter, with me typically 30-4g/hr.
Here's a recent example
2hr 30 on the recumbent in windy and cold conditions. Porridge beforehand about 30g carbs, bolus reduced from 1.2U to 0.4U and TBR of 30% set for 5 hours.
6:30AM – breakfast, 30g, 0.4U, 5.2
8:00 AM – set off BG up to 8.9
Mid ride tests
30min – 3.6, 20g carbs
60min – 4.9, 20g carbs
105min – 3.3, 30g carbs – oops
150min – 4.7, 10g carbs
Lunch – 25g carbs, bolus reduced by 50%, 0.5U, pre 6.1, post 7.0
Learning point – TBR for a long run/ride probably needs to be nearer 20% to avid those big dips in the middle.You can see that I was drifting down lower than my target right from the start. That early drop in th efirst 30 mins is not untypical, so I tend to start eating or drinking from early on, with a mix of quick and shorter acting carbs.
If you want to pick my brains any more go ahead, but this is all based on my experience.
@phoenix is very good at both the theory and the practicalities as well.
