A measure of future U.S. economic expansion continued to improve last week, and the annualized growth rate reached its highest level in over a year, a research group said on Friday.

The Economic Cycle Research Institute, a New York-based  independent forecasting group, said its Weekly Leading Index  rose to 126.7 in the week ended Sept. 21 from a revised 125.3 the previous week. That was originally reported as 125.4.

The index's annualized growth rate jumped to 3.8 percent from 2.7 percent, hitting the highest level since June 2011.