Agree we’re not talking about the “puppy paws” position with forearms on bars and hands dangling out the front in space. But with hands on hoods and forearms horizontal, your forearms are still going to be touching and getting some support from the bars. I think bar choice and hood position is a big part of making this position sustainable. Find a setup where you can get your forearms comfortable resting on the bars while holding the hoods and then more of your weight is supported skeletally not muscularly and there’s less load on your triceps, lats, lower back, etc.
Ironically I’ve realised recently that my winter bike is currently set up better for this than my race bike. Thicker bar tape and bars that angle back slightly from the stem and then have longer drops means my forearms have both more contact area and more cushioning, so I can ride the “aerohoods” position all day long. On my race bike that part of the bar is shorter and with thin tape on, it’s not very comfortable and it’s taken a lot of work to be able to hold the position for long and even so I still get a fair bit of discomfort in my triceps and other supporting muscles.