Superman, 1 arm, 1 leg

Lie face down on the floor with your arms stretched out directly overhead (like Superman flying, hence the name).

Engage your pelvic floor and deeper abdominals (transverse abdominals to brace).

Raise your left arm and right leg into the air at the same time, also raising your chest and head slightly off the floor. Hold there for a second and squeeze the muscles of your lower back.

Lower your limbs back to the ground then raise your right arm and left leg and hold for a second.

You can push down with the hand that is on the ground to help raise your other arm and chest higher off the ground.

This exercise, even though it only uses your limbs as resistance, provides an excellent way to strengthen the lower back muscles.