This exercise is safe, effective and an excellent way to develop core and lower body strength. It may look easy, but give it a try and you'll notice that the longer you hold it, the more intense and challenging it becomes.
Stand with your back against a flat wall. Your
and hips should touch the wall. Walk your feet forward, hip-width apart. Bend your knees and slide down until your hips come close to knee level with your back still pressing against the wall. Raise your arms out in front of you, parallel to the ground. Hold for 10 seconds.
Now move your arms overhead, palms turned inward with your wrists and elbows directly above your shoulders. Be sure that your thumbs and index fingers are touching the wall. Pull your ribs in and contract your abdominals so that your middle back is pressing firmly against the wall. Hold for 20 seconds, breathing naturally. Slide your body back up the wall, lowering your arms as you go.