It probably won't snag them a Nobel Prize, but two scientists have fresh data on a weighty question that many Americans care more about than genes, stem cells or nanotechnology: What can I do about my butt?

Fitness gurus have debated for decades the relative merits of squats, lunges, step-ups, single-leg squats and leg presses in creating the perfectly rendered rear. The one thing they agree on is that better muscle tone will improve your rump, whether it's size or shape you're focused on.

Now two exercise researchers at the University of Wisconsin-La Crosse, have brought rigorous analysis to the problem of posteriors, aided by 12 volunteers who agreed to have electrodes fastened to their derrieres.

John Porcari and Blake Ristvedt theorized that they could determine the effectiveness of different exercises by measuring the electrical activity occurring in the buttocks area during the performance of eight common glute drills. Six men and six women participated in the trial.

Electrodes were placed on three areas of the bare backside, under the subject's loose shorts. Wires traveled under the shorts to a nearby computer for an electromyographic, or EMG, analysis.

After three days of testing over a three-week period, the scientists had their results. For the gluteus maximus, the large muscle comprising most of the cheek area (and the biggest contributor to overall buttock perkiness and beauty), the researchers found that squats generated more electrical activity than vertical and horizontal leg presses, but not significantly more than any of the other exercises.

For the gluteus medius, a smaller muscle just below the waist, on the side, quadruped hip extensions (performed on hands and knees while pressing a leg to the ceiling) were significantly more effective than squats. So were step-ups and lunges.

But be warned: A toned gluteus medius, though it provides nice side shaping, doesn't provide the rear projection favored by fashion-conscious Brazilians and other posterior purists.

The researchers also tested the hamstrings, not because hamstrings contribute to the appearance of the buttocks, but to ensure that the exercises were being performed consistently among subjects.

The take-away message: Whether you're trying to puff up a flat rear or perk up a lackluster one, squats, step-ups, lunges and quadruped hip extensions will all get you a better booty. The good news is that if you get tired of squats, you can switch to other glute exercises without having to worry about sagging returns.

"People think that squats are the best thing," says Porcari, who has written more than 100 scientific fitness articles, including one comparing the efficacy of various sports bras. "This shows that all the exercises do different things, and all are effective to varying degrees."