Getty ImagesAn acceleration of US economic growth is a major risk for investors, says economist Steven Blitz.Blitz warns a "no landing" scenario could lead to inflation rebound and Fed rate hikes.The fed funds rate should be around 4% due to economic resilience, Blitz advises.An acceleration of economic growth in the US might be the stock market's worst-case scenario, according to GlobalData TS Lombard chief economist Steven Blitz.