I swim, up to 2km/80 lengthsat a time. I check my blood before I start & eat a banana (helps to stop cramp too). I also take a bottle of Lucozade sport (32gr carb per bottle) to the side of the pool & depending upon my starting BG, drink some or all of it starting at between 20-40 lengths & ending at 60-70 lengths.
For example, if my BG is 6 before I swim, I eat my banana & will drink all the Lucozade in the first 50 lengths. If it's 10, I'll not start on the Lucozade until 40 lengths in & only drink about half of it.
I'm on a pump & being disconnected while I swim stops my BG dropping too much after about 45 mins (which is when I'll have finished my 2km anyway).
I also find that I have to reduce my basal rate overnight after swimming (I swim at about 18:00, before dinner).
There's a useful American site called
www.diabetesnet.com which can help you calculate how much carb an hour of swimming will use up (for me it's about 65 grammes per hour, I'm just under 11 stone). Your son can then either eat that amount of carb to replace it, or if he's swimming within a couple of hours of a meal, reduce the insulin he has with the meal and add a lesser amount of carb before/during the swim. There's a section within the website about exercise. It's well worth a read. It is an extract from a book called Pumpng Insulin which a lot of people on this forum say is invaluable to pumpers, but the exercise section is equally valid for MDI patients.
Alternatively, try
www.runsweet.com which is a UK site dedicated to diabetes & sport and contains some of the same information, but personally, I find it difficult to navigate :x
p.s. you may need a BG converter (American units to UK units) to use the diabetesnet.com site If you need to convert the values from your meter to the website values & vice versa, the formulae are:
mmol/l (UK unit) x 18.02
mg/dl (US unit) x 0.056
Hope ths is helpful.
