For years, aerobic training consisted primarily of steady state cardio. Think of setting your treadmill for 30 minutes and walking at a steady pace for the entirety of your workout. This sort of cardio will burn calories, but not as efficiently as high-intensity interval training (HIIT), a unique blend of strength training and aerobics. Movements are executed quickly, with little rest in between exercises. Due to its intensity, workouts are done for shorter periods of time. HIIT fluctuates the heart rate, moves more major muscle groups and keeps the body guessing from start to finish.