Basic Bird Dog Exercise
The Basic Bird Dog Exercise is considered a core exercise, strengthening the basic muscles that support the lower back part of your spine.
Kneel on mat on all fours with legs and hands slightly apart.
Raise left arm out straight beside head while raising and extending right leg up out behind body. Lower arm and leg to floor to original position. Repeat by raising and lowering right arm and left leg in same manner. Repeat by alternating between opposite sides. Lift legs and arms deliberately with no jerking.
source: Husky Orthopaedics & ExRx.net