This is incredibly helpful thank you so much for taking the time to write it all out!! It is a really art and you have clearly helped me see what I could do. I don't think I would have been as aggressive with the basal reductions and was very confused about how I would eat lunch and then ride again... but the key is to reduce insulin I see!! I had couldn't ride for about 6 weeks because of wrist op and now in 3 days I am 97% in range which I am very happy about! I am keeping a food and exercise diary for the next 2 weeks to see any trends and help me track everything ready for my next dietician appointment. I'll keep you posted and have a great trip in France!
You're welcome and thanks, finally got accommodation and ferry booked, now just a case of trying to squeeze everything into bags and turning the pedals!
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This has turned into an essay/brain dump and a slightly jumbled one at that, I'm sorry. It may or may not be useful, but even if it's not for you, hopefully someone might benefit
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If anything doesn't make sense, please do ask, likewise if you think there's a better theoretical fit to the data, please go ahead and suggest it - I feel I may well be contradicting myself in some cases below as none of the numbers are particularly hard and fast, it all depends, like all other things in diabetes, plus quite a lot is stuff that happened a few years back now (which I thought might at least add some context even if not very useful for those used to riding a lot). Also n=1, we're all different, etc., etc.
Let's dive in!
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I didn't even think about the option of basal reduction when I first started riding (during lockdown), and it was only a post on a random site somewhere that made me think about it as an option.
I used to take all of my basal in the evening, and really only started reducing it as I'd run low overnight post-ride. I did subsequently also think about and try some evening reductions for rides the next day, but tended to go high overnight and I was also not too keen on needing to commit and make the decision the day before especially as I tended to need to reduce basal even for what I'd now see as short rides of say 50km.
As I've ridden more, I need less basal reduction, so these days a spur of the moment 100 mile ride is just about fine ( as long as I can stop for food) and I don't do spur of the moment 200km rides! Yet!
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Before I started adjusting basal rates (still during lockdown) I usually ended up going really low half way around my ~50 - 80km rides and then needing to eat vast quantities of food, which wasn't much fun. It wasn't helped by the fact that almost nothing was open, so I also had to carry it all with me and sometimes ran out and had to limp home with BG bumping along the bottom (thankfully never more than 20km from home).
Which reminds me that one "advantage" of going low while riding is that if you stop the drop in BG also tends to stop, so you can usually take stock and work out what to do. Still not great if it's late in the evening and cold though.
If you reduce basal you can reduce it too much, I've had ~100km rides where my BG has sat stubbornly at say 9mmol/l and I've generally not wanted to take any bolus for fear of going really low as had been happening pre-basal reduction, so tended to just ride back feeling a bit sorry for myself.
Nowadays if I'm running persistently high/higher than wanted and/or I need some food for energy I'll take 0.5U (or 1U if very high/near somewhere I will stop), which is typically enough to cover ~10g of carbs in normal life, and then will probably need to eat perhaps 40g+ of carbs over the next couple of hours once BG comes down. It's a bit hard to separate the effect of the bolus and that of the basal which is always lurking in the background waiting for your liver to stop/reduce production glucose, though having bolus on board has a definite effect for me for the next 5h while riding (especially obvious if riding after eating lunch and taking reduced bolus), though markedly less/shorter duration during normal life.
Re livers and basal, I find there is a trade-off that I accept whereby I can live with going a bit high when I start a long ride (even when I take some bolus to cover it - but I never want to over-do it and need to start eating loads from the get-go) as my muscle insulin sensitivity isn't yet raised and I also often have some nerves due to the long "unknown" ride encouraging my liver to produce extra glucose via stress hormones, vs the inevitable requirement to eat once my liver has given up/calmed down/run out of glucose (3-5h later) and I have heightened insulin sensitivity (and not much muscle glycogen left).
For this reason, if I take reduced bolus when stopping to eat I will further reduce this (or just not bother) based on how long into the ride I am (knowing that the insulin may still be effective 5h hence) and how long I will still be riding. E.g. Early lunch I might take some (I may also still be running higher than wanted due to FotF/pre-ride nerves), but afternoon tea I wouldn't bother at all unless I was going to be stationary for a long time, but that would be a difficult decision as I'd inevitably run low quite quickly after setting off again. Catch-22.
I am much more relaxed about BG when doing long rides than when I'm at home and don't try to control it as tightly (or indeed very tightly at all) - if I run a bit high for a couple of hours so be it - I will have (perhaps) learned a lesson about what not to do (though different every time!), plus the riding will mean I'll always end up dropping and will also run lower once off the bike (so I tell myself that even being high for a while has some positive effects later). Also, I might quite like to give myself a dose of 0.1U but my pen only does 0.5U min, so I have to live with not bothering. This might be easier to manage with a pump, but I'm not eligible for one afaiu, nor am I really that keen.
For shorter rides (of say 3 or 4 hours) BG is fairly stable and/or easy enough to tweak with some food if needed, it's the longer ones where I accept that stopping to eat uncovered meals will make me go "high" temporarily if I hang around too long, but the trade off is that I can keep riding longer (in the latter part of the day once I start going low) without taste fatigue having yet kicked in.
Last but not least, the libre/CGMs are quite laggy and my BG tends to look a bit like a sinusoid while riding so I tend to need to start eating early, well before the CGM is telling me my BG is dropping/I'm actually heading towards being low.
I now reduce basal less for a given distance (or not at all for <80km, or if I decide to wander out and ride somewhat further), which is probably because I'm fitter so the riding is easier. Though one might assume that would mean less hepatic glucose production, so more food would be needed, which is true to a certain extent, my theory is that over longer rides it means there's not the boom of a massive burst of hepatic glucose at the start followed by the bust of it then running out and going low. Needing to switch from eating nothing for hours to then needing to eat loads doesn't seem to work well for me, I'd prefer to start fairly early with something small and keep going so I feel like eating.
It may also be practice which means more confidence that I can eat my way out of any problems up to a given distance.
The more long rides I do in "a season" the better the effect becomes too, apparently the liver adapts to not splurging all its glycogen at once (I must find a reference to the medical paper I read that in.) First long ride of the year seems to be more difficult than the last one in terms of BG control/boom & bust.
Riding easier definitely reduces liver contribution and one can see a definite change based on how much power you're applying, though as the day goes on this becomes less obvious and may in fact go away completely/is completely obscured by muscle insulin sensitivity + basal effects.
Phew!