"Being able to brace your core and not collapse in any part of your spine demonstrates true core strength and spinal integrity," Rivera says.
Place your forearms on the floor, and extend your legs back, so that only the balls of your feet are on the ground. You should look like a board, from the top of your head down to your heals. Hold for 45 seconds.
To increase the challenge, Rivera says to place something unstable under your forearms or your feet.
Image Source: POPSUGAR Photography / Matthew Kelly