Do this exercise on your hands and knees. Keep your knees under your hips and your hands under your shoulders. Keep your spine in a neutral position (not arched or sagging). Keep your ears in line with your shoulders. Hold for a few seconds before starting the exercise:
Tighten your abdominal muscles and raise one arm straight in front of you, palm down. Hold for 5 seconds, then lower. Repeat 5 times.
Do the exercise again, this time lifting your arm to the side. Repeat 5 times.
Do the exercise again, this time lifting your arm backward, palm up. Repeat 5 times.
Switch sides and do each exercise with the other arm.