The U.S. economy grew more slowly than first thought in April, May, and June, increasing concerns that the world's largest economy could slide back into recession.

Friday's report from the Commerce Department says the economy expanded at a 1 percent annual rate in the second quarter. That is even slower than the meager 1.3 percent growth experts first estimated, and less than investors expected. The report is a routine update made as experts get additional data.

Worries about economic growth mean investors will be watching a speech by the head of the U.S. central bank even more closely than usual later Friday.

Federal Reserve Chairman Ben Bernanke delivers the keynote address at a gathering to top economists at a mountain resort in Wyoming.

Investors and experts have been wondering for most of this week if Bernanke will give any sign of further easing of U.S. monetary policy as a way to support the sagging economy.