For those who want their left brain to get a workout along with their bodies, Tamilee Webb's Science of Fitness series, including I Want That Body!, is are just what the personal trainer and professor ordered. Webb, an appealing and inspiring fitness instructor, includes scientific demonstrations conducted in a lab, showing how her exercises target each muscle group. This disc contains workouts for abs, arms, and buns, and each of those areas is divided into two 15-minute segments. If you're just starting out, do just one segment each; if you really want to up your results, go for both. Webb is encouraging without being off-puttingly perky, and she has the presence of mind, while doing very challenging moves, to calmly remind us of the science behind working each particular muscle. A small complaint: For the arms routine, all she says is to use some free weights; we don't know what size she's using, and there aren't different sizes for the different types of exercises, which can be a good modifier. But if you build in the option of lighter or heavier weights yourself, you should be able to proceed nicely. Extras include a quiz about common exercise forms, nutritional tips and different-angle shots of the routines. If you Want That Body, you better be prepared to work it, but Webb is an accessible leader and trainer and manages to inspire without being a cheerleader. --A.T. Hurley