You cannot strengthen an ACL or an Achilles tendon.
And there were some pretty big powerful backs even way back when.
Petersons playing weight was the same as Dickerson's. Franco Harris was 10lbs heavier than both of them and Greg Bell only 7lbs lighter and a lot shorter.
I'd wager a shiny new penny that RB's haven't increased in size on average anything like Dlineman and linebackers over the last 40 years.
And there will always be outliers.
Gore is just remarkable and I can only imagine he's drinking the blood of teenagers on the quiet.
There is nothing either good or bad, but thinking makes it so.