cardio without killing my legs

[durron597]

recently, i have been trying to put at least 45 minutes of cardio in every day for calorie burning reasons. however, after a month of this my legs are really starting to kill... i don't want to hurt myself / take myself out of commission / or, most likely, make myself sore enough that i get out of the habit of exercising again and thus get off the losing weight track i've been on.

any recommendations on how to keep the calorie burning up but the leg muscle stress down?