Muscle & Fitness says
Most chest and shoulder closed-chain exercises aren't practical for developing strength, so these routines substitute the incline barbell press and barbell overhead press. (emphasis mine)
Yet, a small lady friend sitting on my back while doing push ups works well, gets a nice burn, and feels pretty cool. Now, how to do this without a spotter/partner/lady friend? I thought about throwing plates into a backpack, but that looks awkward. Any suggestions?