You know squats are essential. But they come in so many variations – how can you tell which one is right for you?

Chris Proulx, a professor of movement science and his students tested five different squats – the four freestanding versions shown here, plus one machine exercise. (See “What about Machines?”) Volunteers performed the exercises standing on force platforms, which are high-tech devices that measure the pressure exerted through a lifter’s feet. The researchers also attached electrodes to the volunteers’ legs to see how hard the moves made their quadriceps and hamstrings work. Their pain, your gain.