I have been telling my clients for years that just 15 minutes of interval training is worth significantly more to your health than an hour of a constant, moderate pace, but now here’s an article and a number to back it up.
3 times! That’s right you will burn triple the calories with intervals than you will with a constant pace during your cardio.
You can read more HERE
Obviously, both methods have their uses. An hour of constant moderate pace is obviously going to go a long way towards improving the endurance of your heart and lungs, and especially your legs. But if we’re talking strictly about efficient use of time for calorie burning, intervals are the way to go.
In my own workouts, I try to do both, and alternate between the two. Every other time I focus on endurance, and every other time I do high intensity intervals.