Plank

Facing the floor, the body is elevated and supported by the feet and arms, with the arms straight, as if starting a push-up. Don't: Lift your bum, especially if you're not feeling that strong in the upper body. It puts extra pressure on the shoulders, elbows and the wrists. Most likely the shoulders will be ahead of the wrists, a position that doesn’t use energy efficiently and is unnecessarily exhausting. Glenn Koenig / Los Angeles Times
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