For precisely the same reason that ATG squats are too deep.
Rip
I know that you've said in the past that the weighted dip shouldn't be done to maximum depth. You feel that one should stop going down when their shoulders gets just below their elbows.
Right now, I'm focusing on the weighted-dip as my primary pressing movement. I believe that you've said the weighted-dip can't replace the bench-press because of the instability of the movment? I see exactly what you mean but I'm still sticking with the dip because I enjoy it and I exercise for enjoyment.
I've been going to maximum depth and I'm starting to think that you may be correct about how deep the dip should be preformed. Do you think you could explain to me why your correct?
I was going deep because I thought that I was working more muscles that way. Specifically, I thought that I was working my shoulders and my pecs more that way.
For precisely the same reason that ATG squats are too deep.
Dip with just below elbows = squat with 1" below parallel is for maximum benefits and strength.
I'm curious about this too as weighted dips are my primary pressing movement (currently dipping 105 for 3 reps, super deep). ATG squats shorten the hamstrings, rendering them less able to effectively contract and extend the hips. I'm having difficulty figuring out the analogs with the dipping motion (I'm less familiar with the musculoskeletal system of the upper body).
Cause your relaxing and hence working less muscles?
Think about the moment mechanics between shoulder and elbow. Maximum force is applied to the system at parallel, so that is where the maximum force must be exerted to overcome the load. Any deeper fails to increase the benefit and lowers the amount of weight you can handle.
Bodybuilders seem to get lots of pec work from partial benches, so I suppose it does.
I thought the squat depth rationale was not primarily about moments but about descending until hamstring stretch-shortening is achieved, while maintaining lumbar extension. That is, the point is to work all the muscles properly.
If I apply this reasoning to the dip I would think that one should descend until stretch-shortening is achieved in the anterior deltoid, and perhaps chest.
When one squats too deeply the lumbar spine flexes, but I'm not sure what the analogous thing would be in a dip - perhaps scapular retraction and elevation. I'm not sure that makes sense though.