nothing....its all genetic... you cannot isolate the lower portion of your lats apart from the upper portion. Pure bro-science bullshit!!!
Everything comes down to this.
You can't get "wider" doing wider grips.
You can't isolate the lower pecs or upper pecs.
You can't change the shape or "peak" of your biceps.
You just have to do the best you can with the basic exercises and hope for the best based on your genetics.
There are a lot of otherwise smart people who are really, really dumb when the talk about training.
I think it's because we so badly want to control our destiny/life and we cling onto whatever theories that will makes us feel in control.
We humans aren't logical. We are totally emotional.
Nothing more than muscle heads going into cognitive dissonance thinking they're smart when explaining training and its effects.