Countermovement Jump (CMJ)

The countermovement jump (CMJ) is a simple, practical, valid, and very reliable measure of lower-body power.

Summary

The countermovement jump (CMJ) is a simple, practical, valid, and very reliable measure of lower-body power. As a consequence, it is no surprise that this has become a cornerstone test for many strength and conditioning coaches and sports scientists. The CMJ has been shown to be the most reliable measure of lower-body power compared to other jump tests. Furthermore, the CMJ has been shown to have relationships with sprint performances, one-repetition maximum (1RM) maximal strength, and explosive-strength tests.

This suggests that performances in the CMJ are linked with maximal speed, maximal strength, and explosive strength. When the CMJ is performed using the arm swing, performances can be ≥ 10 % higher than when they include no arm swing. Contact mats, force platforms, accelerometers, high-speed cameras, and infrared platforms have all been shown to provide a valid and reliable measure of CMJ performance – though force platforms are considered as the ‘gold standard’.

This test is not to be confused with the Abalakov Jump test, or any of the Jump-and-Reach tests such as the Sargent Jump test, the Vertical Power Jump, or the Vertical Jump test (i.e. Vertec) (1).

What is the Countermovement Jump (CMJ)?

The countermovement jump (CMJ) is primarily used to measure an athlete’s explosive lower-body power (2, 3), and has become one of the most frequently used tests by coaches and researchers to indirectly measure power in the lower limbs (4). This test can be conducted either with, or without the use of the arm swing. Performing the CMJ with an arm-swing action has been shown to increase performance by 10% or more (5-9).

The CMJ has been measured using contact mats (4, 10-13), force platforms (4, 11, 14-16), infrared platforms (15, 17, 18), accelerometers or linear position transducers (13, 19) and even video analysis (4, 12, 16, 20), though force platforms are often considered as the ‘gold-standard’ for test accuracy. The present issue with measuring the CMJ is the cost and impracticality of some of the aforementioned equipment. Interestingly however, one recent study has demonstrated that CMJ can be accurately measured using a relatively inexpensive high-speed camera (Casio Exilim FH-25 camera) and the KineJump software (20).

Application

As power is a critical component in so many sports (21), and the CMJ is a simple, practical and reliable measure of power in the lower limbs, then it would seem an obvious choice as a tool to measure and monitor performance. To add to this, the CMJ has also been directly linked with 0-30 m sprint performances (22) and relative strength during dynamic 1RM squat and power clean (13) – this suggests that those who perform better in the CMJ, also perform better during sprint performances and 1RM tests such as the back squat and clean.

The CMJ may therefore be an appropriate test for athletes participating in sports which require high levels of explosive strength (i.e. power) such as football (soccer), rugby, basketball, Olympic Weightlifting, and volleyball.

Procedure (How to conduct the test)

It is important to understand that whenever fitness testing is performed, it must be done so in a consistent environment (e.g. facility) so that it is protected from varying weather types, and with a dependable surface that is not affected by wet or slippery conditions. If the environment is not consistent, the reliability of repeated tests at later dates can be substantially hindered and result in worthless data.

Required Equipment
Before the start of the test, it is important to ensure you have the following items:

• Reliable and consistent testing facility (e.g. gym or laboratory).
• One of the following: Contact mat, force platform, linear position transducer, high-speed video camera and software, or an infrared platform.
• Performance recording sheet.
• Relevant calculations (see section ‘calculating CMJ performance’)

Test Configuration
The test configuration for the CMJ will differ depending on what measuring device is being used (e.g. contact mat, force plate, infrared platform, accelerometer, or video camera).

Testing Procedure
Arm-Swing: The test administrator must decide before testing whether to include or eliminate the use of the arm-swing, as it is important to understand that the arm-swing can improve performance by 10 % or more (5). If the arm swing is prohibited, then the athletes must keep their hands on the hips throughout the test. In this case, the test administrator must also pay strict attention to the athlete’s hands to ensure they are not using them to press additional force through their legs.

Countermovement Depth: This is the depth the athlete will drop to during the short ‘countermovement’ or ‘pre-stretch’ action before they take off. Though there is no universal agreement on which depth is most appropriate, higher jumps and peak power outputs appear to increase with larger countermovement depths (23, 24); however, the data is somewhat inconsistent and more research is needed. It is therefore recommended that the test administrator chooses a particular protocol and sticks to it during future testing sessions.

During flight: During their time spent in the air, it is essential that the athletes maintain extension in the hip, knee, and ankle joints to prevent them from achieving any additional flight time by bending their legs (3, 15).

Jump Displacement: It is also important that the athlete not only jumps as high as possible but also attempts to land in the same position as they took off – as jumping forwards, backwards or sideways can affect the test results. To aid this, coaches may often stick sellotape to the floor as a marker for athletes to take off from and land on.

Once the test configuration has been set up, and the test official(s) and the athlete are ready, then the test can begin.

1. With the test apparatus ready (e.g. force platform), the athlete then steps onto the platform.
2. When instructed by the test administrator, the athlete must jump as high as possible and attempt to land in the same location on the platform as they took off from.
3. The athlete must perform a minimum of three jumps so that performance averages can be calculated.

Calculating CMJ Performance

How to calculate CMJ performance
In most circumstances, CMJ performance is reported as either jump height* (cm), or relative peak power output (W·kg^-1).

*Jump height is an estimate of the height change in the athlete’s centre of mass, and is best measured using the impulse momentum data from a force platform (20, 24).

Other test variables such as those listed below may also be measured, but this requires specialist equipment such as a force platform – therefore these are not often measured in most environments. Though measuring those additional variables (e.g. impulse) provides a better picture of the athlete’s physical profile.

• Peak force (N)
• Relative peak force (N·kg^-1)
• Peak power (W)
• Peak velocity (M·s^-1)
• Rate of force development (N·s^-1)
• Impulse (N·s)

In terms of measuring vertical jump performances, flight time* is considered to be the most valid and reliable method for calculating jump height (4, 20).

*Flight time is simply the total duration the athlete spends in the air with no ground contact. Flight time does not start until the athlete loses contact with the floor, and ends the moment they reconnect with it.

The method for measuring jump height using various equipment is as follows:
Contact Mat – If a contact mat is being used, then fight time is typically the outcome measure. However, some contact mat systems may calculate jump height for you. If not, then the test administrator can calculate jump height from flight time data using either of the calculations below.

Jump Height = 9.81 * (flight time)² / 8 (references: 15, 25)
Or,
Jump Height = time² * 122625 (reference: 20)

Force Platform – Those using a force platform are advised to calculate jump height using the following formula (26):

Jump Height = (initial velocity)² / (2 * acceleration due to gravity)

High-Speed Camera – When using a high-speed video camera and appropriate software, flight time is typically calculated via slow-motion analysis. From this, because the flight time has been obtained, jump height can then be calculated using the formulas above.

Accelerometer (linear position transducer) – Similarly to the contact mats, accelerometers typically self-calculate jump height, peak power, and peak velocity – meaning no additional work is needed.

Infrared platform (e.g. OptoJump) – This system calculates jump height by measuring flight time and then performing the abovementioned jump height formulas (15). Therefore, the test administrator is not required to perform any calculations.

Scoring System

Now you know what test apparatus you are using and how to calculate jump height, this next section is very straightforward.

With a minimum of three jumps completed, and therefore three jump height scores, an average score is then calculated. This is done by using the following equation:

• Average Jump Height (cm) = (jump #1 +  jump #2 + jump #3) ÷ total number of jumps (i.e. 3)

Considerations

Then conducting the test there are several factors that need to be taken into consideration before you begin – some being:

• Individual effort – Sub-maximal efforts will result in inaccurate scores.
• Varying take-off and landing positions.
• Arm-swing or no arm-swing.
• Countermovement drop depth.
• Flexing on the ankles, knees, or hips during flight.

Validity and Reliability

The CMJ has been shown to be a valid and reliable measure of lower-body explosive power (3). Moreover, this test has also been shown to be the most reliable measure of lower-body power in comparison to other popular jump tests such as the: squat jump, Abalakow’s jump, Sargent jump, standing long jump, and the standing triple jump (3).

Though the CMJ can be measured reliability using all of the systems below, the force platform is still considered the ‘gold-standard’ apparatus for high levels of precision.

• Contact mats (4, 10-13),
• Force platforms (4, 11, 14-16)
• Infrared platforms (15, 17, 18)
• Accelerometers (linear position transducers) (13, 19)
• High-speed cameras with appropriate software (4, 12, 16, 20).

References