said by LazMan:The plywood add lateral strength to the 2x4 studs...
Pull-out strength on a 3/8" lag bolt is about 200 lbs per inch, so anything more then 2" of thread into the stud, you'll shear the bolt before you'll pull it out. The 3 1/2" bolts I used were overkill.
Just how I did it, and it worked out very well for me...
That's assuming that the physical studs themselves could crack under the weight before the bolts pull out, thus distributing the weight over 4 studs.
But I'd be more inclined to assume that if the wood grain of the stud can hold a grip on the bolt threads, then stud as a whole hold the same force structurally.