Less then 50 years, modern running shoes started in the early 70's and with them increased running injury rates.
Injury rates of who? Seasoned runners or those new to running thinking that a flash pair of Nike's is all they need to run 10 miles?
I've seen studies that concluded cheap running shoes were as good as expensive shoes in terms of impact absorbtion -how did they reach this conclusion, they had people walk (not run) in different shoes. Pointless.