The program is essentially a pure plyometrics workout. This means that you’re essentially always moving, using bodyweight and leg movements to keep the heartrate up. Think of calisthenics (jumping jacks) but always jumping. In addition to this crazy movement, it uses maximum interval training techniques. A traditional exercise has you at maybe 50-60% heart rate for the entire duration or short spikes of activity with long breaks. You either ride a bike for a long time or you workout muscles in batches of 30s with a minute break.
On long periods of activity, biking or running for example, your heart rate spikes, then drops to a plateau. Basically, if you can reach the 3 minute mark, you can reach 30 minutes pretty easy. The largest benefits are in the first 3 minutes though, since your heart rate actually drops after that point and your body plateaus at a given energy burn rate. To put a number on it, let’s say you burn 600 calories in a 1 hour run, for 10 cals/minute on average. Actually what happens is that you burn about 100 calories in the first 3 minutes and then the other 500 calories on the last 57. So 33 cals/min to start then you drop down to 8 cals/min afterwards.
On spike training, like weights, your body spikes into rushes of energy into your muscles burning huge amounts of energy but for very short periods of time. Doing 12 reps of curls might take 30 seconds but you’re only forcing energy for half that time (the way up), then you’re resting for about a minute, giving your body time to recover. Sometimes longer. Not to mention that you’re actively trying to get muscle fatigue that reduces the length of time you can train. If you weight train for an hour at a regular pace, you’re looking at 300 calories burnt, half of what you’d get in the previous example, and you’re building muscle. The actual building of the muscle comes after the workout while your muscles recover.
Next we have interval training. This is what athletes use for their programs because of the way it confuses the body. Remember the first example where the first 3 minutes are the best and then you plateau? Same principle here except that you do it at 80% heart rate for 3 minutes, then drop to 50% for a short period of time (up to the same cycle length), then repeat. In that cycle, you burn about 800 calories and keep the muscles and heart rate confused. Staying too long in a particular range, your body adapts. Move in and out of that range and your body cannot adapt and will always work at 100% effectiveness. P90X does this to some extent but it’s hard to with weights. Still, I can guarantee better weight loss results with P90X that any gym session you’d have.
Finally, we have max interval training. This takes the previous example and focuses the activity and reduces the recovery. You go full out 80-90% heart rate for 3-5 minutes, then a 30 second break and restart. In an hour, you burn 1000 calories, if you can last that long. What also happens is that even when you stop working your heart continues to pump blood and energy into ever muscle for a long period of time. The same thing happens in regular interval training but here, the effect is more pronounced. You can feel it in your body as your heart rate will typically take 30 minutes to an hour to get back to normal resting rate. This has an effect of increasing your post-workout burn rate by nearly 1000% compared to regular training (running).
Wow, all that before I get to the program bits. Insanity uses a max interval training method along with plyometrics for some rather crazy results. One particular program, Pure Cardio, had me go through about 450 calories in 30 minutes. I had an average heart rate of 80% the entire time (since the rest periods are small). I could feel my heart rate for a good 45 minutes after the program was complete as well. Let’s put that into perspective a bit. The average person should eat 2000 calories a day. I burn off 25% of that in a single exercise for 30 minutes and that’s not counting the post-workout burn. In 2 weeks, I’ve lost 6 lbs. The next time I do this workout I will take my measurements for an hour after the workout and compare them to the weight training results I have. I’d be curious to see the comparative results.
All of that to say that if you’re looking for a program to burn through tons of calories in a short period of time, I cannot think of a program that would give better results that this. It will make your weight melt off.