The CMJ Jump Test - What Do The Metrics Mean?

Understanding CMJ Metrics: A Deep Dive into Athletic Performance Evaluation 

The Countermovement Jump (CMJ) is a cornerstone test in sports science, used to assess an athlete’s explosive strength, power, and neuromuscular function. The CMJ involves a rapid downward movement (the countermovement) followed by an explosive upward jump. When analysed using a force plate, the CMJ provides hundreds of metrics that offer insights into an athlete’s performance. In this article, we’ll break down six key CMJ metrics: Jump Height, Peak Power, Relative Peak Power, RSI-mod, Concentric Peak Force, and Concentric Peak Velocity. 

1. Jump Height (cm) 

Jump Height is perhaps the most understandable and widely recognised metric in jump testing. It represents the vertical distance the athlete reached during the jump. There are multiple ways to calculate jump height, in this case we have used the impulse-momentum relationship derived from the force plates to make the results as accurate as possible. 

Why It Matters: 
Jump height is a direct indicator of an athlete’s explosive power. The obvious benefit of having greater jump height is that athletes can leap further and/or higher which helps with actions such as box jumps, dunking in basketball, or receiving a high ball in rugby. 

2. Peak Power (W) 

Peak Power refers to the highest amount of power produced during the jump. Power is the product of force and velocity, and this metric shows how effectively an athlete can convert strength into explosive movement. 

Why It Matters: 
Peak Power is crucial because it encapsulates both the force and the speed of the movement, making it a comprehensive indicator of an athlete’s ability to perform explosive actions. In many sports, the ability to generate high power quickly can be the difference between success and failure. This is brought to life in movements such as 3RM push press, tackling in collision sports, and punching in combat sports. 

3. Relative Peak Power (W/kg) 

Relative Peak Power is the Peak Power normalized to the athlete’s body weight. It’s calculated by dividing the Peak Power by the athlete’s mass, typically expressed in watts per kilogram (W/kg). 

Why It Matters: 
Relative Peak Power is a critical metric because it allows for the comparison of athletes of different sizes and body weights. A larger athlete may produce more absolute power, but a smaller athlete with higher relative power might be more efficient in using their strength relative to their body mass. This metric is particularly valuable in weight-class sports or when comparing athletes across different disciplines. 

4. RSI-mod (Reactive Strength Index-Modified) 

RSI-mod is a measure of an athlete’s explosive strength and reactive ability. It is calculated by dividing the jump height by the time to take off (the duration of the force application). RSI-mod is used to assess how efficiently an athlete can transition from the downward phase (eccentric) to the upward phase (concentric) of the jump. 

Why It Matters: 
RSI-mod is a key indicator of an athlete’s reactive strength, which is essential in sports requiring quick changes in direction, sprinting, and repeated explosive movements. A higher RSI-mod suggests that the athlete can quickly and efficiently recycle energy in continuous high intensity movements such as running and repeated jumping as well as being able to bounce out of the hole of a back squat more effectively. 

5. Concentric Peak Force (N) 

Concentric Peak Force refers to the maximum force generated during the concentric phase of the jump, which is the upward motion after the countermovement. This metric measures the athlete’s ability to generate force against the ground. 

Why It Matters: 
Concentric Peak Force provides insight into the athlete’s maximal strength during the explosive phase of the jump. It’s a crucial metric for understanding how much force the athlete can produce when pushing off the ground, which is a key determinant of jump height and overall power. Athletes who can produce more force can usually express this by lifting heavier weights on squat and deadlift. 

6. Concentric Peak Velocity (m/s) 

Concentric Peak Velocity is the maximum velocity achieved during the concentric phase of the jump. This metric reflects how quickly the athlete can move during the push-off. 

Why It Matters: 
Concentric Peak Velocity is a critical measure of an athlete’s ability to apply force quickly, which is essential for explosive power. In many sports, not only the amount of force but also the speed at which it is applied determines performance outcomes. Higher concentric peak velocity indicates that the athlete can generate force rapidly, which is crucial for activities like sprinting, jumping, and rapid directional changes.