The inverted W or M is a power issue in my book. Those pitchers who have slow stride speeds tend to have more of an inverted W during the stride. I have noticed this with most of young pitchers when I put them through my "Drive Drills," each drive they throw their elbows high in the air because they are trying to use their arms to move their bodies. This always goes away when they develop more power production and start moving faster with the lower half.