Lie on your back with your knees bent, feet flat on the floor and arms along your sides. Extend one leg straight up, then drive through the heel of your grounded foot and lift your hips until your body forms a straight line from shoulders to knee. Lower back down with control, keeping the raised leg up the whole time. One glute is now doing a two-glute job - the test is whether your hips can rise and fall dead level, without tilting toward the unsupported side.

Works: glutes, hamstrings, lower back, core

Breathing: Exhale as you lift your hips, inhale as you lower them.

Common Mistakes: Letting the hips tilt toward the raised-leg side, pushing through the toes instead of the heel, and arching the lower back to fake extra height at the top.

Make Easier: Build up with Bridges on both feet first, or work through Bridge Taps to get used to briefly losing one support.

Make Harder: Hold for a 2-count at the top of every rep, slow the lowering to a 3-count, or do all reps on one side before switching to keep the working glute under constant load.