Steady-state cardio (walking/cycling at a moderate pace) is good for general health and does burn calories. Walking for an hour burns 200-350 calories. You'll need to burn about 3,500 calories to lose a pound, so without diet changes you'll have to walk for 10+ days to lose a pound. But once you stop walking, the calorie burn ends. High-Intensity Interval Training (HIIT) can burn as many as 500 calories in 30 minutes. With HIIT training comes EPOC, which also burns calories after the exercise session ends. Your body goes into an oxygen deficit, and it takes time to replenish your oxygen levels. While your body is replenishing your oxygen levels, more calories are burned. This can occur for 24+ hours. As much as 15% of the calories burned during a HIIT workout will be burned after your workout. So if you burn 300 calories in a 15 minute HIIT session, you'll burn an additional 45 calories while recovering.