Sit in an angled leg press machine and place your feet shoulder-width apart in the center of the footplate. Unhook the safety stoppers and support the weight with your legs. Slowly lower the weight, bringing your knees toward your chest but stopping when your knees are at 90 degree angles. Pause a moment before pressing through your heels to return the weight to the start position at full leg extension but without locking out at the knees.