Countermovement Rebound Jump (CMRJ) test, with ForceDecks

We are excited to announce that CMRJ has been added to the ever-growing list of ForceDecks tests. At VALD we strive for continuous improvement in our technologies based on industry trends as well as feedback from our clients. To better understand how and why to use the CMRJ, we’ve invited Dr Paul Read to answer some questions.

About the author:

Dr Paul J. Read, PhD, ASCC, CSCS*D, PGCE

Paul is the Head of Performance for ACL Rehab Online, a Senior Lecturer in Strength and Conditioning at St Marys University and an honorary Associate Professor at University College London (UCL) and the University of Gloucestershire. Paul is an accredited strength and conditioning coach with both the UKSCA and NSCA, and has consulted with Olympians, professional and international athletes. Paul has authored over 120 research publications and numerous book chapters. His research focuses on assessment strategies of lower limb neuromuscular control in both injured and non-injured athletes and reconditioning strategies to enhance the efficacy of return to performance following injury.

What is the CMRJ test and what does it assess?

An example of a CMRJ being performed on ForceDecks with live in-app results and auto rep detection.Jumping and landing tests require athletes to perform rapid eccentric and concentric actions, assessing key physical components inherent to many athletic movements. The CMRJ combines two different jump types:

1. An initial maximal effort countermovement jump (CMJ), then
2. An immediate rebound jump is performed.

This provides an opportunity to assess slow (CMJ) and fast (rebound jump) stretch shortening cycle (SSC) mechanics in a single test. In other words, it tests the athlete’s ability to perform both powerful and rapid movements – which are essential in sport. 

The SSC is present in many activities and involves a rapid cyclical action including an eccentric phase, followed by a brief isometric transitional period (amortization phase), potentiating an explosive concentric action to accelerate the body.

The classification of SSC type is typically completed using ground contact time (GCT). Assessing slow SSC movement (> 250 milliseconds GCT, i.e., CMJ) provides an indication of mechanical muscle power and elastic strength. Fast SSC (< 250 milliseconds) is more related to reactive strength characteristics, in which the body must apply braking forces to decelerate their centre of mass prior to rapidly creating concentric forces to move in a new direction which has application for change of direction and sprinting.

How can the CMRJ be used in rehab or return to sport scenarios?

By including the CMRJ as part of a return to sport test battery, there is an opportunity to examine if the athlete can effectively utilise SSC mechanics, by converting potential energy into mechanical energy. We can describe the SSC as a spring-like mechanism, where compressing the coil causes it to rebound. When the rate at which the coil is compressed increases, the spring will rebound further.

By including the CMRJ as part of a return to sport test battery, there is an opportunity to examine if the athlete can effectively utilise SSC mechanics

If an individual displays good SSC mechanics and reactive strength, we would expect them to jump higher in a rebound task (i.e., a DJ vs. a CMJ due to the higher rate of loading). Typically, this does not happen, and may be magnified in athletes aiming to return to sport following injury due to observed reductions in athletic physical qualities such as the reactive strength index (Read et al., 2020). Thus, in addition to assessing the mechanics of the respective jumps, identifying deficits in rebound capacity can be useful for informing reconditioning programs to optimise return to sport readiness.

in addition to assessing the mechanics of the respective jumps, identifying deficits in rebound capacity can be useful for informing reconditioning programs to optimise return to sport readiness.

With the use of force plates, further kinetic information can be collected in a time efficient manner to identify known deficits shown following anterior cruciate ligament (ACL) injury, for example. Vertical ground-reaction forces (VGRFs) are associated with knee joint moments, indicating their viability as a surrogate for assessing compensation strategies in knee kinetics and knee joint work. 

Previous research has shown that vertical jumping requires greater contributions from the knee joint than horizontal actions (Robertson and Fleming, 1987). Confirming this, recent work by (Jiaqing et al., 2020) reported that the ankle and knee joints contributed the most to the total positive work in the rebound portion of the CMRJ. Finally, greater ground reaction force asymmetry has also been shown in jumping as compared with change-of-direction tasks 9 months after ACL reconstruction (King et al., 2019), further supporting the use of vertical jumping tests including rebound actions for the purposes of monitoring progress during rehabilitation.

How is the CMRJ different to having athletes perform a CMJ or a DJ test?

When using a DJ assessment, practitioners must consider what is the most appropriate drop height for their athletes. Intuitively, practitioners may wish to standardize the box height (30 cm is often selected to allow for comparisons with previous research). However, when screening a range of athletes, and working with those aiming to return to play, different heights may provide either insufficient or excessive forces for those who all possess varying neuromuscular qualities.

…different heights [of a DJ] may provide either insufficient or excessive forces who all possess varying neuromuscular qualities…

… The CMRJ can help overcome this constraint by assessing landing mechanics after the completion of a maximal vertical jump, providing a height reflective of their individual neuromuscular ability and a more perturbated landing position.

The CMRJ can help overcome this constraint by assessing landing mechanics after the completion of a maximal vertical jump, providing a height reflective of their individual neuromuscular ability and a more perturbated landing position compared to a DJ from a set height.

Rebound protocols have the potential to identify deficits more clearly in landing mechanics associated with ACL injury risk compared with DJ’s (Lloyd et al., 2019). This could be attributed to heightened ecological validity, wherein landing heights mirror those typically observed in individuals during match play. Moreover, forces are regulated by a preceding contraction of the relevant musculature necessary for executing propulsive motions, such as the initial jumping action. This type of assessment may better represent the ability of the neuromuscular system to provide adequate stabilization and force attenuation in response to an individual’s jumping capabilities.

Drop jumping tasks may artificially induce feed-forward stabilization mechanisms, which is a learned skill, developed throughout childhood and adolescence. The pre-planned nature of a DJ assessment requires less of a stimulus-response component, characterized by perturbations to the body’s center of mass. The repeated nature of the CMRJ protocol provides some inherent perturbation and may more accurately reflect the movement demands involved in competition.

The repeated nature of the CMRJ protocol provides some inherent perturbation and may more accurately reflect the movement demands involved in competition.

In which instances would you use the CMRJ instead of a CMJ or DJ in isolation?

The CMRJ is ideal for testing large groups or teams, where performing each jump protocol separately will extend the duration of the test session. In most environments, practitioners operate under strict time constraints; thus, the CMRJ can provide equivalent data to the traditional jump types (Jiaqing et al., 2023) but in a more time efficient manner.

In most environments, practitioners operate under strict time constraints; thus, the CMRJ can provide equivalent data to the traditional jump types, but in a more time efficient manner.

However, the DJ more stringently regulates drop height and, therefore, may be more repeatable for serial measurements

However, the DJ more stringently regulates drop height and, therefore, may be more repeatable for serial measurements

What are best practices when performing the test?

When performing the CMRJ, all individuals should be familiarized prior, ideally in a separate test session or including the movement in the sporting warm-ups. It is also important to standardize the test protocol (hands on hips is recommended) and cueing instructions. A simple approach is to cue athletes to jump ‘fast and high’. It is advised that the GCT remains < 250 milliseconds in the rebound portion of the jump. Longer contact times invalidate the assessment of fast SSC and reactive strength and suggest either the test has not been cued correctly, or the athletes lack the required physical capacity to effectively perform the movement. 

In addition to GCT, measurement of jump height and reactive strength index (RSI) provide quantifiable ‘output’ metrics. To understand the movement strategy, it is also prudent to measure other kinetic variables.Examples include:

• Centre of mass depth,
• Phase duration,
• Braking and propulsive impulse, and
• Stiffness (the ratio between the peak ground reaction force and displacement of the centre of mass).

However, practitioners are encouraged to examine the reliability of these metrics in their own context / setting to ensure meaningful change can be detected over time.

If you would like to know more about to leverage data from ForceDecks technology in your setting, please contact us.

References

• Jiaqing Xu, Turner A, Comyns TM, Harry JR, Chavda S, Bishop C. Countermovement Rebound Jump: A Comparison of JointWork and Joint Contribution to the Countermovement and Drop Jump Tests. Appl. Sci. 2023, 13, 10680. https://doi.org/10.3390/app131910680.
• King E, Richter C, Franklyn-Miller A, Wadey R, Moran R, Strike S. Back to normal symmetry? Biomechanical variables remain more asymmetrical than normal during jump and change of direction testing 9 months after anterior cruciate ligament reconstruction. Am J Sports Med. 2019;47:1175-1185.
• Lloyd R.S, Oliver JL, De Ste Croix M, Myer GD, Wass J, Read PJ. Comparison of Drop Jump and Tuck Jump Knee Joint Kinematics in Elite Male Youth Soccer Players: Implications for Injury Risk Screening. Journal of Sports Rehab. doi.org/10.1123/jsr.2019-0077.
• Read, P. J., Davies, W. T., Bishop, C., Mc Auliffe, S., Wilson, M. G., & Turner, A. N. (2020). Residual deficits in reactive strength indicate incomplete restoration of athletic qualities following anterior cruciate ligament reconstruction in professional soccer players. J Athl train, 2020.
• Robertson DGE, Fleming D. Kinetics of standing broad and vertical jump. Can J Sport Sci 1987;12:19-23.
• Yoshida T, Kariyama Y, Hayashi R, Takahashi K, Zushi A, Zushi K. Development of multistep drop jump test by usingdifferent drop heights. In Proceedings of the 33 International Conference of Biomechanics in Sports, Poitiers, France, 29 June–3July 2015.