Hi
@n1ck, Please tell me if I am inadvertently telling you how to suck eggs. I was told many years ago that to cope with exercise;
1) eat food beforehand or 2)
lower the insulin which is active during the exercise or 3)
a combo of 1) and 2).
Also
not to exercise if BSL at start of exercise is > 13 to 14 mmol/l as the body responds to this by releasing glucose from the liver during the exercise and one ends up with BSLs much higher and feeling very unwell.
The above advice (we are talking about 50 years ago)! was augmented by the statement, during exercise your BSL may go up, stay about the same or go down. (these doctors were not going to get caught out, they had the cricket field of questions covered).
So,
I tend to find my BSLs go up during exercise, when starting BSL is , 13 mmol/. So eating food first off was not a very successful way to mange things initially. Also I soon found that indulging in vigorous games like squash were counterproductive because my BSL would be in the high teens at the end of exercise and if I was not careful a hypo followed by a rebound hyper would happen some 6 + hours later.
The other point which most of us have had drummed into us (but not 50 years ago - where experience was very much by trial and errors - not pens, pumps, glucose meters or fancy insulins) was that
BSLs can really drop at about the 6 hour mark after the end of exercise. Why ? Apparently our muscles have glucose stores within them. It makes sense to have fuel stored in your aircraft near the engines in order to take off at short notice.
So what happens when the muscles (or aircraft engines) become low on fuel after a 'normal' bout of exercise or flying? Fuel (glucose) is replenished from fuel lines (the blood stream) and for whatever reason that tends to be about 6 hours or so after the exercise (flight) etc. Whether the intervening time is spent on maintenance who knows?
When glucose is 'sucked up' by the muscles the blood sugar in the blood stream may drop , unless a larger meal has been consumed to make up the short fall, or insulin is lower in quantity and so more blood sugar is left in the blood stream.
So for me the answer was to lower the insulin that was acting some hours after my exercise rather than the insulin working during exercise itself.
If my exercise lasted much longer than expected and I found that I had reached a point where my BSL was getting lower I could always have a boost of food.
At age 64 I walk carrying the shopping and arm and leg weights rather than run, swim slowly, avoid squash. Enjoy non-competition tennis, do kayaking, canoeing and walking on the beach. I used to cycle, run, do whitewater canoeing etc.
I appreciate that people of my age still run and do more energetic activities than I. It was a matter of what suited me best and still would meet my health needs, heart-wise in particular.
On my insulin pump I lower my basal rate by 20 to 30% for 4 hours or so at the beginning of exercise. The Novorapid lasts about 5 hours per dose input, the fall off in insulin takes maybe 2 to 3 hours to start having an appreciable effect on BSL and will last past the 6 hour mark. I vary the % reduction and time course depending on the length of exercise and strain (heavier shopping load vs lighter, longer trip, any break between to and fro etc). So there is still some guesswork!!
No sure if that helps but it seems to work for me. For others food might be needed during exercise as a matter of course. Best Wishes !!!
BTW I suspect that the cost of Dopplers is the reason why they are scarce these days.
..........(thought I might be a tad low anyway 
