Garage Storage – Purpose of This Garage Shelving Support Item

garageshelvingstoragesupport

So for part 3 in the continuing saga of weird stuff in my house, the garage. In particular, this odd looking thing attached to the wall:
Shelf???
I thought it might be a shelf, but all of the supports are on top, which is an odd way to build a shelf. It is also too high up (about 7 feet off the ground) to be practical for storage. The cable and pulley looking thing might lead you to believe it was meant to be retractable, except, as you can see from the side view, it is quite firmly bolted into the masonry:
Shelf??? side view
The way the supports are placed, it looks designed to resist an upward force from below, but I have no idea what the intended use case for it could be.

Best Answer

@Ecnerwal and @UnhandledExcepSean, I believe you are correct. Looking at this thing from below, I can see screw holes where a speed bag was probably mounted in the past. Bottom of shelf Closeup on mounting holes