Cardio Box is not a very difficult workout but it does come with some stipulations: all exercises are performed on the balls of your feet. Throw your bodyweight behind punches by turning the foot that's on the same side with your punching arm and bend your knees when performing Upper Cuts so that you use your legs to drive the punch upwards! Do all that and your lungs will feel it. Add EC and your muscles will too!
Extra Credit: 1 minute rest between sets.