Recently, I've been obsessed with...

 ...customizing the Scientific 7-minute Workout (http://well.blogs.nytimes.com/2013/05/09/the-scientific-7-minute-workout/). I started doing this workout as prescribed, but soon realized I needed to bump up the duration for every part of the circuit. I also added hip raises to get a bit more of a back and glutes workout. Have you tried it yet? What do you think?