The multi-stage fitness test (MSFT), also known as the beep test, bleep test, PACER (Progressive Aerobic Cardiovascular Endurance Run), PACER test, FitnessGram PACER test, or the 20 m Shuttle Run Test (20 m SRT), is a running test used to estimate an athlete's aerobic capacity (VO 2 max). The test requires participants to run 20 meters back and forth across a marked track keeping time with beeps.