Come onto your right forearm with elbow under shoulder and feet stacked. Lift hips up as high as possible, forming a straight line from head to heels. Extend left arm directly over shoulder and press right hand into the mat. Keep core engaged the entire time. Hold for 30 seconds each side. For an extra challenge, lift your left leg up as well (photo).

Straight-Arm Plank With Shoulder Touch

Place hands under shoulders and come up onto the balls of your feet. Keep arms straight and gaze toward the floor. Squeeze shoulder blades together and draw your belly button up toward your spine. Keep quads and glutes engaged the entire time. Hold for at least 30 seconds, up to one minute.

Place hands under shoulders and come up onto the balls of your feet, keeping feet wider than hip-width. Keeping hips still, bring right hand up to touch left shoulder. Return to center and bring left hand up to touch right shoulder. Continue to alternate, keeping torso and legs as still as possible. Perform for at least 30 seconds, up to one minute.

Source: Mind Body Green