So I've gone from Standard Interval training to what is known as HIIT Interval training. The idea here is to get in and hold VO2 Max i.e. Heart Rate over 90% for a pre-determined interval and repeat this over and over once you have recovered. You only want to do maximum efort for a combined total less than 20 minutes of your total workout. Lastnight, since I've been doing this for a number of months. I did a 20 combined 20 minute max in 35 minutes. I could tell I was really working! I didn't lose but a 1/2 lb but gained about 1 lb in muscle mass according to my scale. If you start out you shouldn't exceed 12 total or combined minuteso f maximum effort. Initally you'll feel like you are trying to commit suicide after you torture yourself. Google HIIT Interval trainging, you'll learn a lot, you'll burn fat.