Eek -- I'm sitting here shaking. After lunch, my dexcom said 152 and my meter said 133. I ate a spoonful of peanut butter and did a 30 min (moderate) workout. Right after, my dexcom suddenly dropped from 82 to 55 and buzzed. I figured it was an error, but grabbed juice just in case, then tested ... 32!? So weird, I've rarely dropped this fast.

Sorry -- I basically just needed to complain! (But, maybe people have a better suggestion for a pre workout snack if I'm not on the low side before starting?)

When I workout it's usually running 2.5 miles or so.  I always check before going and try to be at least 200 or so when I start.  If I'm below that I eat 15-30 carbs before leaving.  Seems to work out pretty good.  I know this probably isn't for everyone, but seems to work for me.

If you're starting a new workout there's a good chance you'll go super low the first few weeks.  Then your muscles will probably get more efficient and not steal as much glucose from blood to replace glycogen stores. 

In the meantime you may need to drop overall insulin dose and run a little high pre-workout like DDrumminMan suggested.  It's cool that you have the dexcom to warn you of lows.  And if you haven't read it before, check out The Diabetic Athlete by Sheri Colberg.  Her book was the first thing that helped me understand the weird effect exercise has on blood sugar. 

I often don't plan ahead for my workouts so I'll drink a juice box while I'm working out and it prevents me from going low.

Both to keep myself hydrated and to keep my BG up, I take a water bottle with me to the gym. It's a 16oz bottle.  I fill it about 2/3 full with Gatorade, then top off with water.

Trial and error is the best advice I can give.

For example, only in the past few weeks, I have found that 2 boxes of raisins eaten beforehand will keep my blood sugar rock stead for about an hour of running.  Freaky but something I only discovered through trial and error.

I usually eat one glucose tablet right before I work out, and it seems to keep my blood sugars in a "normal" range when I'm done. Nothing's worse than getting done exercising and shaking and having to eat or drink alot to correct it! I always try to make sure my blood sugar is in the upper 100s before I start working out.....hope this helps!

I like to eat 30g carbs and 7g protien before I go running (4-7 miles) and I reduce my insulin at the snack by 50%. It seems to work pretty well as long as I'm not low before the workout, in which case I would have a juicebox with 15g carbs, and wait 15 minutes to recheck then start the workout.

I run about 5 miles a day and rarely have low blood sugar issues as long as I don't bolus within 2 hours of my workout.  If I absolutely have to eat, I take 1/4 of the insulin I would normally require.  Everyone's different though, so you just need to experiment until you find a formula that works well for you.  Also, I recently went on a CGM and clearly saw that my blood sugar rises about 30-40 pts in the first 1/2 hour, then begins to fall back down.  I knew this was expected, but it was kind of interesting to verify it on my own.

Sarah, I always eat quick acting carbs before exercising. I love my Tootsie Pops, 15 carbs. I take a long walk for one hour on roads with hills on good weather days, while enjoying the Tootsie Pop. It works out just right. Other times I exercise very soon after a meal which gives me plenty of carbs. Peanut butter digests too slowly for a pre-exercise snack.

You did drop a lot though. Was it a cardio type of exercise? Did you have insulin on board? Those are important things to be considered.