McNair has only missed 3 games out of the last 64 NFL regular season possible starts. He is as durable as any QB in the NFL.
The Titans RB situation is miserable. I'm not high on Brown at all. He runs too high, isn't elusive enough to avoid hard hits, and has yet to prove he can last a season without getting injured. They will have a backfield by committee this year since they really do not have a feature back. Brown did well in spurts last year but the coaches kept giving the bulk of the carries to a broken down George and his 3 ypc. I can see Smith and Brown splitting the carries.