U.S. productivity grew at an annual rate of 2.2 percent in the third quarter. It marks a slowdown from the previous quarter but is still better than the weak gains seen for most of this nine-year expansion. Labor costs accelerated but still remained at a low level.

The Labor Department says the rise in productivity in the July-September period follows a 3 percent rate of gain in the second quarter, which had been the strongest increase in three years. Labor costs rose at a 1.2 percent rate after having fallen at a 1 percent rate in the second quarter.

Productivity, the amount of output per hour of work, has been weak throughout the current recovery. Analysts have been unable to come up with definitive reasons for the slowdown.