Plank

1. Start by lying face down on ground, place forearms on ground so elbows are underneath the shoulders.
2. Press up the body so the arms make a 90 degree angle
3. Make sure that the body is as straight as possible (parallel to floor), and make sure to breathe
4. Hold and tighten core for the designated amount of time

Progression: Add weight to back, elevate feet, perform on one foot and/or arm, or unstable surface