Oh I’m sorry, overloading? There’s no such thing. If it was practical, we would carry a wheelbarrow with us full of equipment just to show those normal people with a compact camera how and what a real professional looks and carries. We have want to contend ourselves at any cost. Even if it means we’ll probably have a bad back by the time we’re 50… or 45. In some cases 40, and 35. Heck, after the first year of carrying heavy shit, we’ll either be worn out or bulk as hell. That’s what separates the pros from the amateurs. Those who can carry, and those who can not.
As long as you can pull off carrying one main camera, two backups and at least five lenses (two telephotos) along with your backpack full of shit we will never use anyway – you’re fine. But if you can’t, and if you complain about your back, then this job is not for you.