Hi
@hynes48
I'm starting on a pump this Monday due to my cycling regime, I had exactly the same issue as you and I'm MDI.
I've done allot of work on my control and with insulin dosage I've found the following:
Daily Commute: Cycle 30km each way with 300meters elevation. The night before I cycle I would reduce my basal insulin (in my case Lantus) by 15%, in the morning I take 50% of my normal Bolus insulin and eat my normal breakfast (porridge) and start my ride about 45 minutes after eating breakfast.
Halfway into my ride to work is the hilly bit and have been stopping to take BG levels after all the climbing. This is where my control was falling apart as I found that the climbing obviously burns the carbs and was going low to around 2.8mmol/L. I then found that when I got to work without treating this low would result in a huge spike to 18-21mmol/L, which is your Liver and adrenaline producing the survival spike.
Now I take 2 water bottles, one carrying water with an SIS tablet and the other with Lucozade sport., I ensure that I'm sipping on the sport drink (usually have 50% from a 500ml bottle) prior to the climbing which keeps me on target throughout the ride, I now get to work wth a BG of around 5.2mmol/L (perfect).
Once at work I will take the other 50% of my morning insulin Basal rate and this then keeps me smack on target until lunch time.
If I cycle the next day I will reduce my Basal rate further by an additional 5% (20% total) as my sugars just keep dropping without this correction and then I'm eating more calories than I'm burning.
Cycling is a tough sport as its both Anaerobic and Aerobic, therefore it can really mess with your control unless you identify the areas of impact. I Highly recommend you think about the areas your working hard and then stop and do a BG test to confirm. I use to be a bit shy about my diabetes but due to the benefits that the testing has given me I now don't think twice about stopping and testing in public as its the only tool we currently have to understand what's going on.
I've also cycled on 200Km Audax events which last all day in the saddle and for these events I will test every 30Km and reduce my basal insulin by 20% the night before.
It seems to work, but diabetes will always throw some curb ball in to the equation that will keep you guessing 'what on earth went wrong?'.
Good luck and don't let it beat you, its a bit of work, but life is so much better once its controlled.