Squeeze glutes (butt) and raise up into a bridge. Return to ground in controlled manner.
Note: the primary muscle working should be the glutes (butt), not the quads (front of leg) or lower back. Be sure to initiate the movement by squeezing the glutes.
Perform 1-5 sets of 8-12 reps per leg. Or, perform 1-5 sets of 20-40 second intervals (doing as many reps as possible during those intervals).