The multi-stage fitness test (MSFT), also known as the beep test, bleep test, PACER test (progressive aerobic cardiovascular endurance run), or the 20m shuttle run test, is a running test used to estimate an athlete's aerobic capacity (VO₂ 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. A second caution ends the test for that runner. The number of shuttles completed is recorded as the score of that runner. The score is recorded in Level.Shuttles format (e.g. 9.5). The maximum laps on the PACER test is 247,^[1] which former Central Middle School student Dennis Mejia achieved,^[2] the only person to ever reach such a level.

The test is used by sporting organizations around the world along with schools, the military, and others interested in gauging cardiovascular endurance, an important component of overall physical fitness. The multi-stage fitness test is also part of most health-related fitness test batteries for children and adolescents, such as Eurofit,^[3] Alpha-fit,^[3] FitnessGram^[4][3] and ASSOFTB.^[5]

The multi-stage fitness test was first described by Luc Léger^[6] with the original 1-minute protocol, which starts at a speed of 8.5 km/h, and increases by 0.5 km/h each minute. Other variations of the test have also been developed, where the protocol starts at a speed of 8.0 km/h and with either 1 or 2-minute stages, but the original protocol is nevertheless recommended.^[7] The test appears to encourage maximal effort by children. Additionally, the test's prediction of aerobic capacity is valid for most individuals, including those who are overweight or obese.^[8]

Prior to the test commencing, runners line up at the 0m marker, facing the 20m marker. Following a countdown, a double beep or voice cue signals the start.

1. Runners commence running towards the 20m marker
2. At or before the following beep, runners must reach the 20m marker. Touching with a single foot is acceptable
3. At or after, but not before, the same beep, runners commence running back to the 0m marker
4. At or before the next beep, runners must reach the 0m marker
5. At or after, but not before, the same beep, runners start the next circuit (i.e. back to Step 1)

Every minute or so, the level changes. This is signaled, usually, by a double beep or, possibly, a voice cue. The required speed at the new speed level will be 0.5 km/h faster.

Notes: The distance between the "start" and "turn around" markers is usually 20m; however, the test can also be carried out using a 15m track. Shuttle completion times are modified in proportion.

Leger specified a 1-minute protocol: that is, each level was meant to last approximately 1 minute. However, because speed changes mid-shuttle confuses matters, the algorithm for a change in level is as follows: "the next level commences on completion of the current shuttle when the absolute difference between the time spent at the level and 60 seconds is the least".^[9]

VO₂ max, or milliliters of oxygen per kilogram of body mass per minute (e.g., mL/(kg·min)), is considered an excellent proxy for aerobic fitness.^[10] Attempts have been made to correlate MSFT scores with VO₂ max. Do note that such estimations are fraught with difficulty as test scores, while substantially dependent on VO₂ max, also depend on running efficiency, test familiarity, anaerobic capacity, personal drive, ambient temperature, running equipment (floor, shoes) and other factors.

A paper by Flouris, et al. (2005) determined the following:

${\displaystyle VO_{2}\max =({\text{maximal attained speed}}_{{\text{in}}\ {\text{km/h}}}\times 6.55-35.8)}$^[11]

An earlier paper by Ramsbottom, et al. (1988) suggested the following:

${\displaystyle VO_{2}\max =14.4+({\text{Level}}\times 3.48)}$^[12]

Luc Léger, the originator of the multi-stage fitness test, never did patent it. Consequently, organizations around the world have been able to incorporate subtle variations into the test. The most common^[4][13] variations are:

The introductory explanation of one multi-stage fitness test, the FitnessGram PACER test, has been widely spread as a copypasta, meme, and through other comedic ways due to the test's modern use in schools, primarily in physical education classes. The voice of the introduction was Roger Francisco, who had worked at Prairie Production Group, which provided video and audio spots for Human Kinetics.^[15][16]

• Harvard step test, a cardiovascular test
• Physical fitness test
• Yo-Yo intermittent test