Speaking from experience, I definitely agree with this.
Try this simple little workout: repetitive sets consisting of three exercises - ten squats (body weight only), five or six pushups, and five crunches. If you can work your way up to thirty minutes of this at a good pace, you will be surprised at the energy you will burn.
You can substitute other bodyweight exercises for the pushups (pullups, dips, etc.).
You can do this anywhere - all you need is a few square feet of floor space.
Trust me, it's a lot more demanding than it sounds.
Thanks!
Funny you should mention the sets of exercises. As a warmup, one of my old instructors used to have us do a combo of 3 things. We'd start with 2 jumping jacks, drop down and do 2 pushups, stand up, drop back down and 2 situps, stand back up and repeat. Sounds simple and easy but once you get going, it kicks your butt. Good times though!!:ultracool
Mike