Countermovement Jump (CMJ)

Contents of Article

1. Summary
2. What is the countermovement jump (CMJ)?
3. Who should use the countermovement jump test?
4. How do you conduct the countermovement jump test?
5. How do you calculate countermovement jump performance?
6. What is the countermovement jump scoring system?
7. Considerations for using the countermovement jump test
8. Is the countermovement jump test valid and reliable?
9. Can the CMJ manage and assess fatigue?
10. Tips for using countermovement jump tests
11. References
12. About the Author

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 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).

Who should use the countermovement jump test?

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 0-30m sprint performances (22) and relative strength during dynamic 1RM squat and power clean (13) – this suggests 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 that require high levels of explosive strength (i.e. power) such as football (soccer), rugby, basketball, Olympic Weightlifting, and volleyball.

How do you conduct the countermovement jump 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 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 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 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 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 tape 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 performance averages can be calculated.

How do you calculate countermovement jump 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. However, 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 (25):

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.

What is the countermovement jump 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 for using the countermovement jump test

Before 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.

Is the countermovement jump test valid and reliable?

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).

Can the CMJ manage and assess fatigue?

Managing fatigue from training is crucial to maximise athlete adaptation, while simultaneously minimising injury risk and reducing overtraining. Therefore predicting and monitoring the fatigue status of an athlete is imperative. Still, it can be difficult for coaches and teams operating at amateur sporting levels who are not privy to large financial budgets and don’t have sport science or medical teams. If this is the case, the countermovement jump (CMJ) test may be an effective strategy to monitor fatigue. 

Neuromuscular fatigue is characterised by a reduction in force and power due to fatigue of physiological mechanisms within the musculature. Research from more than 10 years ago has shown the effectiveness of the CMJ test in assessing neuromuscular fatigue (6). Including the CMJ test throughout the course of a sporting season can successfully highlight neuromuscular fatigued players to coaches (27). 

A study by Balsalobre-Fernandez et al. (2014) monitored 15 middle/long-distance runners over a consecutive 39-week period (28). Interestingly, they reported a significant correlation between CMJ performance and other fatigue markers such as rate of perceived exertion (RPE) and cortisol levels. Another finding of the study was that the CMJ measured the week before the best performance of the season was significantly different from the CMJ measured the week before the worst performance of the season. CMJ was measured once a week by recording the average of three jumps with hands placed on hips. 

Another study conducted by Balsalobre-Fernandez et al. (2014) investigated the impact a race ranging from 800-5000m has on CMJ performance (29). CMJ height was measured 90 minutes before the race and after the race. CMJ height was significantly lower after completion of the race and correlated with increased cortisol levels and RPE scores. The authors of this study put forward the CMJ as a suitable assessment to monitor fatigue during competition for middle to long-distance runners.  Research in sports such as rugby and Gaelic Football has also supported the use of the CMJ to assess fatigue (30, 31). 

It is not just the sporting setting where the CMJ test is used to monitor fatigue. Research from Welsh et al. (2008) found the CMJ test can significantly detect fatigue in U.S. Marines during sustained operations (32). Interestingly, they found just one CMJ trial to be effective in detecting fatigue and there was no advantage in performing five trials compared to one trial.  

Potential issues

The CMJ is a quick, non-fatiguing, and easy-to-administer test to assess neuromuscular fatigue,  but there are some issues to be aware of. Cormack et al. (2008) suggest when athletes are fatigued, they alternate their jumping mechanics to achieve a desired jump height and potentially deceive the test (37). Therefore, it is advised to use measures such as contraction time rather than solely using jump height if access is available. 

The CMJ is a reactive movement derived from the stretch-shortening cycle (SSC). Reactive movements can be further categorised into fast or slow SSC movements. The CMJ is considered a slow SSC movement, and fast SSC movements like a drop jump may offer a greater insight into neuromuscular fatigue. 

For coaches working with recreational or amateur athletes, having the appropriate devices or software to assess contraction times and fast SSC movements is unlikely. However, it is important to understand using CMJ jump height to assess neuromuscular fatigue may not be 100 % accurate but can still be a strong guide. A poor CMJ score should not be used to determine fatigue. It should alert the coach to investigate the athlete further to establish if they are fatigued. 

Best practice for fatigue assessment

If using an app such as MyJump2 or having invested in an affordable jump mat to implement the CMJ as a method to assess and monitor neuromuscular fatigue, the testing procedure needs to be strict and consistent for the best results. Usually, three trials of the CMJ test are recorded – it is common for both the best score and average score to be used. However, Claudino and colleagues (2017) suggest using the average score across trials when using the CMJ to monitor neuromuscular status (33). Using the average score in CMJ testing is more sensitive in detecting fatigue compared to using the best jump score. 

It is advised to perform jumps without an arm swing. The arm swing, as alluded to earlier, can increase jump height and it is best to keep hands on hips for trials. Rest times of 60 seconds between trials appear to be sufficient for recovery.

Cues/instructions given to the athlete when performing a CMJ test need to be standardised – it is important the same cue with the same speech tone and volume is given by the tester. If a tester changes the cue or provides the cue in a more motivating tone than normal, it could potentially influence the athlete’s jump performance. Therefore, it is more beneficial to use an external cue such as “jump as high as you can towards the ceiling” rather than an internal cue “jump as high as you can, extending your ankles, knees, and hips”. However, even more importantly, the cue must remain the same for every testing session.

Perhaps using Z-scores is a good choice in assessing CMJ scores. A Z-score gives an idea of how far from the mean a data point is. CMJ scores should be recorded and can be analysed using Z-scores. A Z-score one point from the mean which McLean et al. (2010) used, could be an effective strategy in monitoring fatigue (30). 

It is important to use the CMJ in conjunction with other metrics like RPE or simply having a chat with the athlete. Asking an athlete how they are feeling can sometimes be the most powerful feedback mechanism available to coaches.

Tips for countermovement jump tests

• Set up the application or jump mat in the same place 
• Record CMJ score before the training session after a standardised five-minute warm-up
• Use the same instruction with the same tone for every trial
• Perform three CMJ trials with hands on hips and 60 seconds rest between trials
• Record scores and input into software like Microsoft Excel or Google Sheets for assessments
• Use data analysis to assess changes (Z-scores suggested)
• Changes or drops in CMJ performance warrant a discussion with the athlete
• Training sessions can be altered, and load reduced if the athlete is fatigued
• Long-term CMJ performance should be tracked to avoid overtraining or burnout