I lift two 8-lb. weights up and down a few times until I notice the people next to me lifting quadruple that amount, practically rolling their eyes at me. By the time I lay down on the mat to do a round of abs, I'm exhausted. I'm closing my eyes and pretending I'm back in Mrs. Kay's kindergarden class and this is nap time.
Pretty much any activity that gets your blood pumping is cardiovascular. When your heart rate rises, muscle cells break down sugar and fat for fuel, burning calories. Clearly there are a ton of ways to do this, but exercise physiologists lump cardio into three buckets -- long, slow distance (LSD), medium hard (tempo) and high-intensity interval training (HIIT).