Start resting on all fours with a medium-weight dumbbell — 10 pounds is a good starting point — on the left side of your body.
With your palms flat, raise up off your knees onto your toes; your legs should be straight. Be sure to gently squeeze your glutes to engage them and keep your hands directly underneath your shoulders.
Contract your abs to keep yourself up and prevent your bottom from sticking up. Remember to keep your belly button pulled in.
With your head and spine in line, keep your back flat — don't let it curve. Look about one inch out in front of you, and don't tuck your chin. Picture your body as a long, straight board.
Bend your elbows and begin to lower your body down to the ground. Be sure to keep your spine in a neutral position and your core engaged. Go as low as you can in the push-up position without sacrificing your form. With control, drive your palms into the ground, pushing your body up and return to a high plank position.
From here, grab the dumbbell with your right hand and pull it underneath your body until it's on the right side of your body. Be sure not to rotate your hips.
Next, perform a push-up and then return to the high plank position.
With control, grab the dumbbell with your left hand and pull it underneath your body until it's back on the left side of your body.
This counts as two reps.
Perform this exercise for 40 seconds, then take 20 seconds of rest.