The Luc Léger, multi-stage fitness test (MSFT), also known as the beep test, bleep test, PACER, 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 (V02 max).

The test requires participants to run 20 meters back and forth across a marked track keeping time with beeps. Every minute or so, the next level commences: the time between beeps gets shorter; participants must run faster. If a participant fails to reach the relevant marker in time, they are cautioned