players don't run out of gas in the 4th quarter which says their conditioning is good. If it were not, I would think it would cost us games. At that point I suspect changes would be made. You're lacking strength if your opponent defeats you. I don't see a lot of that due to strength, especially on defense.
By the looks of the bodies on some elites at the combine, there is a lot of HGH going on. I don't have proof, but I have eyes. They don't take blood for testing HGH. Regardless, the S&G coach doesn't determine who plays. Being strong and making plays aren't one and the same.