If you low carb and exercise, you can still have carbs to manage your BGs. For example, when I run I know I'll need 2 dextrose every 15 mins to maintain my BGs; whereas if I do weights, my BGs will rise so I know I won't need carbs.
If I find I'm hypoing after exercise - I'll take dextrose - you must always treat hypos with short acting carbs.
If you're on insulin you can adjust your insulin to suit. For example, on a morning without exercise I'll take 3 units of Novorapid for an omelette, whereas when I exercise in the morning, I'll need 1 unit.
There's a great book called Think Like a Pancreas that tells you how to moderate insulin as your pancreas would do.