The pack test replaced as of the late 1990s an earlier physical fitness test called the step test, which measured physical fitness based on beginning and ending heart rate after a short workout on a set of stairs. It was believed that the pack test more accurately measures the ability to perform arduous labor for a sustained period of time (e.g. 45 minutes) than the step test. Besides the U.S. Forest Service, all other federal and most other state and private agencies also use the pack test although there are a few state and private agencies which still use the step test.