Plank
How to: Place your forearms on the ground, with the elbows aligned below the shoulders, and arms parallel to each other, about shoulder-width apart. Place feet hip-width apart or closer together to challenge your stability and make this exercise more difficult. Ground your toes into the floor and squeeze your glutes to stabilize your body. Keep your head in a neutral position by looking at a spot on the floor a few inches in front of you.
Make it easier: If you’re having trouble with a forearm plank, try one with the palms of your hands on the floor instead.
Pushup
How to: Start in a plank position with both hands placed on the floor, shoulder-width apart, and feet placed hip-width apart. Keep your head in a neutral position, meaning you’re looking at the floor and your ears are positioned over your shoulders. The rest of your body should be in a straight line from the crown of your head to your heels.
Brace your core, then bend your arms, lowering your body until your arms are at approximately a 90-degree angle and then return to start position with arms fully extended. To make this more challenging, you can place your feet closer together to narrow your base of support.
ATA 