Single Leg CMJ Test: Protocol and Symmetry Assessment

The Single Leg Countermovement Jump (Single Leg CMJ) is the unilateral version of the vertical countermovement jump. If the bilateral CMJ is one of the most widely used power tests, the single-leg version adds a key layer of information: how each leg performs independently in a vertical movement with an elastic component — something that horizontal unilateral tests (single leg jump, triple hop) don't capture in the same way.

What does this test measure?

It assesses explosive vertical strength of a single leg, including the stretch-shortening cycle component (the countermovement). It allows you to calculate the Limb Symmetry Index (LSI) in the vertical plane, complementing the indices obtained from horizontal jumps.

What you'll need

• A contact mat, force plate, or vertical jump app with a camera
• Enough space to maintain balance on one leg
• Optional: a nearby wall or support for the initial setup only (not during the jump)

Testing protocol

1. The athlete stands on one leg on the mat or in front of the camera, with the free leg bent backward and hands on the hips
2. Cue a controlled countermovement (knee and hip flexion of the support leg) immediately followed by a maximal vertical jump on the same leg
3. Landing must be on the same leg, in a controlled manner, without the free leg touching the ground
4. The system records flight time and calculates jump height
5. Repeat with the other leg
6. Perform 2-3 valid attempts per leg and record the best result from each side

Common mistakes

• Letting the free leg "help" by touching the ground at any point during the jump or landing
• A countermovement that's too deep or too slow, which changes the nature of the test
• Not alternating the order of legs, leading to accumulated fatigue
• Comparing this test's height directly with bilateral CMJ height without accounting for the fact that it will naturally be lower

How to interpret the results

The key metric is the Limb Symmetry Index (LSI):

$$LSI (\%) = \frac{\text{Height of affected/non-dominant leg}}{\text{Height of healthy/dominant leg}} \times 100$$

LSI	Interpretation
≥ 90%	Adequate symmetry
80-90%	Moderate deficit
< 80%	Significant deficit, prioritize specific unilateral training

As a reference, Single Leg CMJ height is typically between 60% and 75% of bilateral CMJ height in athletes without significant asymmetries.

How it relates to other tests

This test rounds out the unilateral battery by adding the vertical component with countermovement:

• Single leg jump test — the horizontal version without a countermovement, easier to introduce first
• CMJ (Countermovement Jump) test — the bilateral reference point to contextualize unilateral results

Track and monitor progress

Asymmetries in the vertical plane don't always match those in the horizontal plane, so it makes sense to track both. With Movalytics you can log each leg's jump height at every assessment and compare how the vertical symmetry index evolves alongside the horizontal one, giving you a much more complete picture of the rehab process or the athlete's overall status.

Frequently asked questions

Is this very different from the horizontal single leg jump? Yes — although both are unilateral, this test includes a vertical countermovement with an elastic component, while the single leg jump is a horizontal jump without that component. They can reveal different asymmetries depending on the plane of movement. When should this test be introduced during return-to-sport? Generally in advanced phases, once the athlete is already comfortable with bilateral countermovement jumps and horizontal unilateral jumps without discomfort. What if the vertical and horizontal LSI don't match? That's quite common. Each plane of movement can reveal different deficits, so it's worth training both components (horizontal and vertical) specifically based on each test's results.