deadlift

This move may seem simple, but it's a terrific way to tone your butt. All you need is a set of dumbbells. Read more on Refinery29
The Mistake: Starting the move with the hips too low. The Fix: If the hips are too low during a conventional deadlift, the
Find a coach and learn to deadlift. You may have no interest in pulling 1,000 pounds, but smart people know that stronger is better, and the deadlift is very good at making you stronger the right way.
Of course, even the very best flat-stomach workout isn't going to do much for you if those nice muscles you build are covered with a layer of nature's comfortable camouflage -- a.k.a. fat.
Position a loaded bar on the ground and walk your shins close to the bar. Before lifting, shift your weight onto your heels
Your back should be flat, chest up, and shoulders down the entire time. Initiate the movement by moving your hips back. Keep