5-Factor Fitness: The Diet and Fitness Secret of Hollywood's A-List, by Harley Pasternak (Putnam, $21.95)

Client Names Shamelessly Dropped Halle Berry, Christian Slater, Eve, ex-Julia Roberts tool Benjamin Bratt.

Credentials Cited An MS in exercise physiology and nutritional sciences, University of Toronto; trainer certification by American College of Sports Medicine.

The Gimmick Five weeks; five, five-minute workout phases, five workouts a week; five meals a day, five minutes to prep and cook.

Observations Each workout features two conventional dumbbell exercises and one core exercise, framed by five-minute cardio sessions. The workout is challenging but over quickly. The most plain-vanilla exercises of the books featured here, but the format is unique. Pasternak wiggles out of the five-minute box by saying you could do more cardio at the end if you want. You should.

Best for Folks willing to work hard in exchange for a shorter workout, who like to keep exercises simple and can abide a detailed program that invites no modifications.

20-Minute Burn: Four New High-Intensity Workouts, by Matt Roberts (Dorling Kindersly, $15)

Client Names Shamelessly Dropped Sandra Bullock, Naomi Campbell, Mel C, Faye Dunaway.

Credentials Cited Former competitive sprinter; trainer certifications by American Council on Exercise and American College of Sports Medicine.

The Gimmick "Peripheral Heart Action" (PHA) workouts arrange strength exercises so they deliver cardio benefits too. Book offers four different workouts: fat-burning, muscle-sculpting, adding muscle and building endurance.

Observations Excellent color pictures, clear text and good mix exercises for home and gym. The purportedly 20-minute fat-burner has 26 exercises plus warm-up and cool-down; it took at least 40 minutes each time we tried it. Other workouts are said to take 30 or 40 minutes, but you may need to double that. The programs do get the heart a-poundin' and the muscles a-burnin', however. A slim paperback, it's the most gym-portable of the bunch.

Best for Beginners looking for explicit directions and exercise variety -- and willing to work out longer than the advertised times. By editing workouts, it's possible to stay within the 20-minute goal.

The Ultimate New York Body Plan, by David Kirsch (McGraw-Hill, $21.95)

Client Names Shamelessly Dropped Heidi Klum, Liv Tyler, Faith Hil.

Credentials Cited Founder of Madison Square Club in New York, 15 years of training experience; spokesman for the Almond Board of America; sells lines of food and spa products; has appeared on "Today" and "Extreme Makeover."

The Gimmick Ultimate Fitness, Ultimate Nutrition, Ultimate Motivation, Ultimate Maintenance. And achievable in two weeks (!), if you believe and commit!

Observations Punishing workouts that are advisable only by the already fit. Purported 45-minute body-sculpting workout includes 40 (!) exercises, many of them challenging and novel. This reporter completed no more than 30 of them in two tries of more than an hour each, and was asked in the locker room afterward if he was okay. (He was.) Oh, and after that you're supposed to do 45 minutes of cardio. One has to wonder if anybody tried to do this workout in 45 minutes before it was put in this book. The book is full of motivational hoo-ha that would make Depak Chopra giggle.

Best for Veteran gym rats skilled at functional core exercises yet looking for something that can kick their butts -- or for some novel moves to add to their repertoire.

Body Express Makeover: Trim and Sculpt Your Body in Less Than Six Weeks, by Michael George (Fireside, $24.95)

Client Names Shamelessly Dropped Meg Ryan, Reese Witherspoon, Tobey Maguire, Christian Slater (Christian, you promiscuous training client!).

Credentials Cited Certifications by American Council on Exercise and National Association of Sports Medicine; martial artist devoted to East-West integration; spokesman for Nike.

The Gimmick Three workouts (from brief-easier to long-harder) mix weight training, calisthenics and aerobics with yoga- and Pilates-derived exercises into very challenging but doable workouts.

Observations Equivalent exercises tailored differently for men and women; our (middle-aged, fit but not athletic) female tester liked the workouts a lot. Once learned, the exercises are the best of the bunch in the books reviewed here. The routines can almost fit into the time allotted, though advanced workouts require three sets of 20 reps of 10 exercises, so cancel your appointments and bring your sports drink. Clear instructions and photos; varied, challenging and effective exercises.

Best for Moderately fit exercisers looking for a well-scripted, challenging, realistic program that will deliver results for far more than six weeks.

-- Craig Stoltz