Why does the phenomenal increases in the standard of living in the US correlate and track with inflation?

Prior to the Federal Reserve and it's elastic effect on monetary policy, the annual average inflation adjusted income of a typical US citizen was between 7000 to 13000 dollars. Most people had to live in multifamily units and all but the most basic necessities were within the average persons reach. The average mortality was between 45 and 50 years old. After the inception of the Federal Reserve, and especially after Keynesian economic policies.. the middle cl has grown and tracked with inflation. How can this success for almost 100 years be explained?