The Countermovement Jump – More Than Just Jump Height

2024-12-03 09:45 Articles

The countermovement jump (CMJ) is a widely used method to assess lower-body explosive power in sports performance. It’s a dynamic movement involving both an eccentric (stretch) phase and a concentric (shortening) phase, providing key insights into an athlete's physical capabilities and areas for improvement.

What Makes the CMJ Valuable?

The CMJ offers more than just a measure of how high an athlete can jump. It provides detailed performance metrics and descriptive indicators, revealing the "how" behind the result. For instance, it helps answer questions like:

⏺︎ Was the athlete quick off the ground?
⏺︎ Are they powerful but lack speed?
⏺︎ Did they perform a shallow or deep jump?

By examining both the outcome (jump height) and the movement patterns, coaches can gain a comprehensive understanding of an athlete’s strengths and weaknesses.

For a deeper dive into how vertical jump testing can be applied to athlete monitoring, strength assessment, and rehabilitation, check out our article The Ultimate Guide to Vertical Jump Testing. This comprehensive guide explores key metrics and strategies to enhance training and recovery outcomes.

Application Across Sports

From basketball to rugby, volleyball to sprinting, the CMJ is a reliable and practical tool for monitoring performance and tracking progress. Even sports without a major vertical component benefit from CMJ assessments because vertical force is the foundation of all human movement—even in sprinting, where vertical force drives forward momentum.

With tools like the AiKYNETIX Web Platform, measuring these metrics has never been easier. The app provides accurate, lab-quality insights, such as force-time curves (like the one shown above), breaking down the jump into distinct phases to evaluate movement efficiency and productivity.

Body Weight Phase

The Body Weight phase, often called the weighing or stance phase, marks the start of the CMJ. During this phase, the athlete stands still for at least one second, ensuring accurate measurement of their body weight in Newtons. This silent period is critical as it establishes a baseline before movement begins, reflected as a stable force level on the force-time curve.

Relevance in Sports and AiKYNETIX Analysis

On the AiKYNETIX Web Platform, the Body Weight phase provides key data for monitoring an athlete’s weight trends over time. The Report feature displays fluctuations, helping coaches and athletes assess weight stability and its potential impact on performance. The graphic below demonstrates the ground reaction forces (GRF) during this phase for four consecutive jumps. Variations between colored lines (blue, orange, green, red) may highlight subtle differences in balance or posture across attempts.

This initial phase is essential for ensuring valid and reliable CMJ analysis, making it a foundational step in assessing athletic performance.

Braking Phase

The braking phase marks the start of active movement in the CMJ. During this stage, the athlete initiates a countermovement by relaxing key muscles, allowing for flexion at the hips and knees, along with some dorsiflexion at the ankles. This phase begins when the measured force drops below the athlete’s body weight, signifying a moment of free-fall as the body descends. Negative velocity characterizes this phase, as the athlete continues to accelerate downward. The graphic below highlights where the breaking phase occurs on the force-time curve.

Why It Matters in Sports Performance

The braking phase is crucial for setting up the subsequent stages of the CMJ. Efficient braking allows athletes to better prepare for the transition into the zero-velocity and push-off phases, ultimately improving overall jump performance. In fact, the energy absorbed during braking directly impacts the energy generated in the following phases, as seen in the equivalence of their force-time curve areas.

Athletes who struggle with this phase often show reduced efficiency in their movements, which can limit explosive power and overall jump height. By analyzing the braking phase, coaches and athletes can identify areas for improvement and optimize movement patterns for better results.

Zero Velocity Phase

The zero-velocity phase of the CMJ is a critical moment when the athlete decelerates their center of mass (COM) as it transitions upward. This phase begins immediately after the braking phase when force applied by the athlete returns to system weight, and COM velocity shifts from its peak negative value to zero. Despite the term "zero-velocity," the athlete is still moving downward during this phase, reaching the lowest point of the countermovement. The graphic below highlights where the zero-velocity phase occurs on the force- time Curve.

Importance in Athletic Performance

This phase reveals how effectively an athlete can decelerate their body, reflecting the ability to control eccentric muscle actions. It can also indicate overall movement efficiency, as challenges in this phase may suggest areas for improvement in strength, control, or coordination.
Practitioners can use insights from the zero-velocity phase to identify weaknesses and design targeted exercises, such as eccentric training or plyometrics, to optimize performance. Understanding this phase is key to refining movement patterns for greater explosiveness in athletic activities.

Push-Off Phase

The push-off phase, often called the concentric or propulsion phase, is when the athlete generates maximum upward force to extend their hips, knees, and ankles, propelling their center of mass (COM) vertically. This phase begins as soon as the COM velocity becomes positive, marking the transition from deceleration to upward momentum. It represents the explosive effort that powers the jump. The graphic below highlights where the push-off phase occurs on the force- time Curve.

Importance in Athletic Performance

This phase is a critical measure of an athlete's ability to generate force and power effectively. Key metrics analyzed during the push-off phase include average or peak relative propulsive force and power.

Efficiently transitioning from the zero-velocity phase to push-off demonstrates an athlete's ability to convert stored energy into upward momentum.

For athletes struggling in this phase, training programs may include specific exercises like Cleans, Trap Bar Jumps, or Pin Squats to improve propulsive power. By optimizing performance in the push-off phase, athletes can maximize jump efficiency and achieve better overall results in power-based movements.

Flight Phase

The flight phase in a countermovement jump (CMJ) starts the moment the athlete's feet leave the ground. This phase represents the peak of the athlete’s effort, aiming to achieve the maximum vertical displacement of the center of mass (COM) before gravity brings them back down.

Defined as the interval between take-off (when ground reaction force drops below a threshold) and landing (when the athlete reconnects with the ground and force exceeds the threshold again), the flight phase is straightforward yet crucial. During this time, no external forces other than gravity act on the athlete. The graphic below highlights where the flight phase occurs on the force- time Curve.

Why Is It Important in Sports?

The flight phase is the culmination of all prior phases—braking, deceleration, and propulsion. It reveals how effectively the athlete generates and transfers momentum into the air. Measuring the duration of the flight phase and the corresponding jump height can provide valuable insight into an athlete’s explosive power and performance in sports requiring vertical jumps. For coaches and athletes, monitoring trends in flight time can track improvements in strength and power output.

Landing, Damping, and Stabilization Phases: Managing the End of a Jump

The final stages of the countermovement jump (CMJ) involve three critical phases: Landing, Damping, and Stabilization. These phases ensure the athlete safely transitions back to the ground and regains control after the jump.

Landing Phase

The landing phase begins the moment the athlete makes contact with the ground after the flight phase. During this time, the athlete absorbs the impact force and applies a net impulse equal to the propulsion impulse, decelerating the center of mass (COM) from its downward velocity to zero. The height of the jump determines the landing velocity, with higher jumps leading to more significant impact forces. This phase ends when the COM velocity stabilizes at zero.

Damping Phase

Following the landing, the damping phase is where the athlete actively controls and absorbs the residual forces from impact. This phase is crucial for managing joint and muscle loads to prevent injury. The athlete works to stabilize their body by engaging muscles to dissipate the energy from landing. It’s a transitional phase where control and efficiency play a significant role in minimizing the risk of overloading the lower limbs.

Stabilization Phase

Finally, the stabilization phase marks the athlete’s return to a balanced, steady posture. This phase is characterized by the athlete’s ability to remain still and maintain control over their body. It ends when all forces return to baseline levels, reflecting full recovery from the dynamic movement. Stabilization highlights an athlete’s balance and readiness to transition into the next movement. The graphic below highlights where those phases occur on the force- time Curve.

Application in Sports

These phases are vital for performance and injury prevention across various sports. Monitoring landing mechanics can reveal discrepancies in how each limb absorbs force, offering insights into potential asymmetries or imbalances. Damping efficiency shows how well an athlete controls impact forces, while stabilization assesses balance and readiness for subsequent movements. Together, these phases help evaluate an athlete’s overall biomechanics, balance, and injury risk.

A Comprehensive Approach to Assessing the Countermovement Jump

When evaluating athletic performance through a Countermovement Jump (CMJ), Jump Height often takes center stage. While valuable, focusing solely on this metric limits the depth of insights available. Historically, Jump Height became the primary benchmark because early tools like Vertec devices, jump mats, and even simple wall-and-chalk methods only provided basic data. However, these options often inflated results and failed to capture the full biomechanical picture.

Modern force plates revolutionized CMJ analysis by offering a detailed look at the process, not just the outcome. Jump Height represents the vertical displacement of an athlete's center of mass (COM), but it’s merely the result of a complex chain of events. Every phase—from braking to flight—plays a crucial role in determining performance. Metrics like Reactive Strength Index and COM velocity at takeoff now offer deeper insights into an athlete’s ability to apply force effectively and transfer momentum efficiently.

The Advantage of AiKYNETIX Technology

AiKYNETIX elevates CMJ analysis with its Web Platform and iOS App, offering tools that surpass traditional methods. Unlike force plates or standalone devices, AiKYNETIX integrates AI-driven motion tracking with accessible, single-camera input to deliver laboratory-grade accuracy. Here’s how AiKYNETIX stands out:

• Comprehensive Data Analysis: While traditional tools focus on jump height and time, AiKYNETIX evaluates each CMJ phase in detail, helping practitioners understand how force is applied and momentum is transferred.
• User-Friendly and Scalable: The AiKYNETIX iOS App requires minimal setup, making it perfect for athletes and coaches in various settings without the need for expensive hardware.
• Performance Monitoring Over Time: The platform tracks and visualizes trends in performance, offering benchmarks for progress, profiling, and recovery.
• Injury Risk Management: By analyzing phase-specific mechanics, AiKYNETIX helps identify inefficiencies or asymmetries, guiding tailored interventions to reduce injury risk.
• Actionable Insights for Training: Beyond jump height, AiKYNETIX provides advanced metrics such as RSI (Reactive Strength Index) and braking efficiency to inform training programs.

Why CMJ Assessment Matters

Assessing the CMJ offers benefits for athletes across sports, whether for monitoring progress, benchmarking performance, or guiding recovery programs. The detailed data from AiKYNETIX ensures coaches and practitioners can make informed decisions about training adjustments, enabling athletes to maximize their potential.

By bridging accessibility and precision, AiKYNETIX makes professional-grade biomechanics insights available to everyone, ensuring that every jump counts toward better performance and reduced injury risks. If you're curious to see how AiKYNETIX can transform your CMJ assessments, schedule a demo or reach out to our team today.

Antoine Mattier