When your blood sugar is low the last thing you want to do is run around. Lows are treated with a food/drink that has carbs in it. When a type 1 diabetic has a high blood sugar, they usually treat it with a shot of fast acting insulin (which is the same insulin they take with every meal). Exercise also helps to lower it.

EDIT: in response to Sandy H: Typically a type 1 diabetic recognizes when they're having a low blood sugar and are able to treat it themselves without the help from someone else. If they do collapse from a low, you should give them a shot of glucagon (if they have it) and/or call 911.