Michael Esco, PhD, CSCS of WebMD posted a review on Insanity. Here are some snippets.
The Insanity workouts are highly intense and designed for people who are already in good shape. It is not intended for special-need populations, such as cardiovascular, pulmonary, and metabolic disease patients, diabetics, or obese people, and people with orthopedic limitations. If you are extremely unfit and looking for an “easy fix”, then Insanity is not for you. The program will work best for people who already exercise on a regular basis and are willing to work hard.
The program takes a huge amount of self-discipline and dedication. As with any home-based exercise regimen, the various distractions that often occur can easily interfere with the workout program.
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Insanity...the name says it all. It is a maximum intensity workout program that will push you to your physical limits and will test your mental toughness. It’s great for cardiovascular fitness and achieving a lean body, but it is intended for people who are already at least fairly fit. The workouts are very challenging and require a great amount of dedication and willpower to complete.
You can read the full article here.