Depends on what the goal of the exercise is. For the majority of people who need to be in better health, zone 2 cardio is what they need rather than increased c

Depends on what the goal of the exercise is. For the majority of people who need to be in better health, zone 2 cardio is what they need rather than increased caloric burn. You can't look for time efficiency with zone 2 cardio - you just have to do it for enough time to build conditioning. Depending on the person, zone 2 might be running, but for most people a brisk walk is enough.