It certainly looked against Louisville that the lineman were not strong enough.
This can be poor S&C, too much banging in practice, and/or not proper rest.
Brian Kelly for many of his flaws had that regimen down to a science where ND wasn't having guys blow up all the time. He would talk about knowing when and how to rest guys so they're ready for kick off. It's no secret CMF practices are more intense than Brian Kelly's.
This team needs rest and hopefully have enough juice not to get the brakes beat off next Saturday before the bye.