There are certain lifts that inspire awe, confusion and envy. Overhead squats are just such a lift, those that can’t do them trash them, those that can speak softly of their usage of the lift because boy its a humbler. Now Im not saying you should replace front squats or back squats with the overhead squat far from it. The overhead squat is a great warm-up/accessory lift possibly one of the best. As a warm-up (usually done last) it pulls you through a range of motion that requires solid thorasic extension, combined with excellent hip knee and ankle mobility.
As a heavier accessory lift, it punishes the upper back, core (is that still a term) and the uncoordinated man or woman, the slightest wobble can throw the lift out, the back and erectors contract isometrically the keep everything in place. Want to make your life more miserable try them with a clean grip (my preference). The time under-tension on heavier lifts is surprising especially when done for high reps as you must keep tight the whole time.
These are a great lead in exercise with the goblet squat for junior or novice athletes because it teaches them good postural habits and good mobility, remember strength training done the right way can match or out perform stretching for flexibility gains. Mastery of this lift makes front and back squatting seem like nothing (more squat progressions later this week). Its what Dan John calls it an exercise that turns your “body into one piece”, its one of those lifts once mastered allows you to turn your hand to most others.
For many just the bar or even 40kg will be enough when dipping a toe in the overhead squatting pool, focus on hitting good form with bar held over the ankle or shoulder blades as you drop into a full squat. For most people hitting decent shoulder extension is a huge issue. I like to use over head reaches on a foam roller and band dislocations (The warm-up Jon Erik Kawamoto lists here for the snatch works excellently for OH squatting too). Even though its been some what abused by the “functional” fitness crowd for whom it is an athleticism measure, but it shouldn’t be a bench mark. Do it get good at it reap the benefits and move on.
It might sit in a program something like this
Bar OHS end of warm-up
Deadlift/Front Squat etc
OHS 2 x 8-10 (first week) up volume to 3-4 sets eventually (start small 20-40kg)