Lots of useful info on this thread!
Firstly, it might help to take a look at this movie:
To reply to your question
@Zanshin, the high BGs you experience after a bout of high intensity exercise will be down to your body's hormonal response to your elevated heart rate. Hormones (initially glucagon and then hormones such as adrenaline and epinephrine) trigger your liver to release glucose into your blood stream. Lactate build up is a bit of a red herring and
@borofergie, (a competent exerciser on low carb) is right when he states that the body utilises different fuel sources depending on the intensity. (See attached graph below)
The issue with taking insulin before you exercise is that if you risk a rapid fall in BGs - particularly if you don't actually raise your heart rate high enough to trigger your liver to release glucose.
A safer option is to firstly at the end of an intensive bout of exercise, have a 'cool-down' period where you do something aerobic and less strenuous for a further 20 - 30 mins. What this will do is allow your heart rate to fall and put an end to your body's stress response (and stop signalling the message to release glucose) The liver doesn't 'switch' off producing glucose for quite a while after a bout of exercise, so by doing a bit of less strenuous aerobic exercise, you can help your body 'mop up' the extra glucose the liver is producing.
A second option is to take some insulin after you finish your exercise. This will encourage the now depleted muscle cells to re-stock with glucose (stored as glycogen). Something to bear in mind however is that your exercise has created an energy 'deficit' in your body. What I mean by that is that your exercise has not only resulted in burning inter-muscular glycogen stores, but it has also caused your liver to release a load of its own stores of fuel. Consequently, unless you replace this with food (where appropriate with a reduced bolus) you risk your blood glucose levels falling low later on after your exercise session.
A third option (and one which is my own personal opinion based on observation, not on scientific study) may work for some and not for others, and is probably reliant on any beta cell function you have left (insulin producing function). In a healthy pancreas insulin and glucagon have opposing effects - insulin is secreted when food is on the way, or to lower BGs, and glucagon (produced by alpha cells) is secreted when there is a need to raise BGs. It is commonly recognised, that most people with T1D retain a very small amount of beta cell function. Consequently, if you eat something (no need for it to contain carbs) after you exercise, it could be enough to trigger the pancreas to secrete enough insulin to override or suppress the glucagon response, and hence moderate the liver's release of glucose.
For more info go to :
www.teambloodglucose.com or join the TeamBG or Sporty Diabetic FB pages.
TeamBG will be doing parkrun Harrow on 01 August, and have other events planned too. It's an opportunity to get together with others with T1D or T2D to share strategies to maintain healthy BGs with exercise (well, that and have a bit of a laugh!). Why not join in?!