CrossFit Seminar Staff member James Hobart demonstrates the Overhead Lunge here, which is a more challenging version of the back and front rack lunges we looked at previously. The instability of moving forward, while also shifting up and down while you lunge, makes it very difficult to hold the barbell overhead.
Keeping your feet hip width apart thoughout your lunging steps is good for creating more stability in all forms of the lunge, but especially so with the Overhead Lunge.
As with the other forms of the lunge, you could start with lunging on the spot and stepping backwards to create a bit more stability and work up to full depth once all your alignment is in place. A great modification for those starting out with this movement is to hold a plate overhead instead of the barbell.