What a jump test shows about knee recovery

Written by the SOS Clinic physiotherapy team.

After a knee injury or an ACL reconstruction, many people judge their progress by how high they can jump. If the jump looks good, it is easy to think the knee is back to normal.

A jump on force plates tells a fuller story. It shows how each leg pushes, how each leg lands, and whether one side is quietly doing more of the work.

What is a countermovement jump?

A countermovement jump is the jump most people do without thinking. You stand tall, dip down quickly, then spring straight up. You land and settle.

At SOS Clinic, this jump is done on ForceDecks force plates. These are two flat plates, one under each foot. They measure how hard each foot pushes into the ground, many times every second, all the way through the dip, the push and the landing.

Why jump height can hide a weaker leg

When you jump on two legs, your body finds the easiest way to get off the ground. If one knee is weaker or less trusted, the other leg often does more of the pushing. The jump can still look high, even though the two legs are not sharing the load evenly.

Studies on force plates back this up. A large review of people after ACL reconstruction found they jumped lower on average than people without an injury. It also found differences between the legs in how force was produced, which jump height alone did not show.¹ A study of professional soccer players found that differences between the legs in pushing and braking were still present more than nine months after surgery, even as jump height improved.²

What the test looks at

Your physiotherapist looks at more than one number. In plain terms, the test shows

• The dip. How well each leg controls the body on the way down, a bit like braking.
• The push. How much force each leg puts into the ground to drive you up.
• The landing. How each leg takes the impact when you come back down, and whether you shift onto the stronger side.
• The timing. How quickly you can turn the dip into a push.

These details show how you move, which helps shape the next part of your program.

A balanced result is only part of the picture

A result where both legs look even is a good sign, but it does not always mean the injured leg is back to full strength. Sometimes the legs look more even because the uninjured leg has lost some strength, since it has also done less work during recovery. One study of non-elite athletes found that much of the improvement in balance between the legs came from the uninjured leg getting weaker, while the operated leg stayed about the same.³

Comparing one leg with the other can also overestimate how well the knee is working. One study compared the operated leg with the other leg’s strength before surgery. Many people who looked even on the day did not reach the level their good leg had before the injury.⁴

The opposite can happen too. In a study of elite skiers, the difference between the legs faded over time, but overall jump power stayed lower than in uninjured skiers for years after surgery.⁵ So your physiotherapist looks at how strong and springy you are overall, as well as how even the two legs are.

One test is not enough on its own

No single jump can decide whether you are ready for sport. A study of basketball players late in ACL rehabilitation found that some jump tests picked up differences between the legs and others did not, and the authors suggested using a group of tests.⁶

At SOS Clinic, the jump test sits beside strength testing on the ForceFrame strength frame, hop tests, a look at how you move with the HumanTrak 3D motion camera, and how your knee feels and responds. Your physiotherapist puts all of this together to guide your program.

Is a jump test safe for me?

Jump tests are used only when they suit your stage of recovery. After surgery, they are done only once your surgeon has cleared you for jumping and landing. Follow your surgeon’s advice on timelines and any limits. Before that point, your physiotherapist can test your strength in other ways that do not involve impact.

If your knee is swollen, painful or giving way, the jump test waits until it settles.

How SOS Clinic can help

The physiotherapists at SOS Clinic in East Melbourne rehabilitate people before and after ACL reconstruction, whoever their surgeon is. They also see people with other knee injuries who want to return to sport with confidence.

A biomechanical profile assessment brings the force plates, strength frame and motion camera together in one visit. Repeat tests show how each leg is changing over time, so your program can be adjusted as you go. You can read more about ACL injuries and knee physiotherapy at the clinic.

When to get help sooner

Contact the clinic or your surgeon promptly if your knee gives way, swells up quickly after activity, locks or catches, or becomes hot and red. The same applies to calf pain or swelling after surgery, a fever, or a wound that is red, weeping or opening. During opening hours, contact the clinic. After hours and on weekends, go to your nearest emergency department.

Book a biomechanical profile assessment at SOS Clinic

Frequently asked questions

Can I do a jump test soon after ACL surgery?

Not straight away. Jump testing only happens once your surgeon has cleared you for jumping and landing. Until then, your physiotherapist tests strength and movement in safer ways.

If I jump as high as before, am I ready for sport?

Not always. Jump height can look good while one leg is still doing more of the work. Your physiotherapist checks how each leg pushes and lands, along with strength, hop tests and how your knee feels.

Does the test hurt?

It should not. The jump is a normal movement and you do a few practice goes first. If it causes pain, the test is stopped.

How often should the jump test be repeated?

It depends on your stage of recovery. Many people repeat it every few weeks or at key points in their rehab, so changes can be seen and the program adjusted.

Is a jump test only for people after ACL surgery?

No. It can help after other knee injuries, and for athletes who want to check how each leg is working before a season.

References

1. Labban W, Manaseer T, Golberg E, Sommerfeldt M, Nathanail S, Dennett L, Westover L, Beaupre L. Jumping into recovery: a systematic review and meta-analysis of discriminatory and responsive force plate parameters in individuals following anterior cruciate ligament reconstruction during countermovement and drop jumps. J Exp Orthop. 2024;11(2):e12018.
2. Read PJ, Michael Auliffe S, Wilson MG, Graham-Smith P. Lower limb kinetic asymmetries in professional soccer players with and without anterior cruciate ligament reconstruction: nine months is not enough time to restore “functional” symmetry or return to performance. Am J Sports Med. 2020;48(6):1365-73.
3. Edwards P, Blackah N, Radic R, Ebert J. Vertical jump asymmetries from 6 to 9 months following anterior cruciate ligament reconstruction with hamstring tendon autograft in non-elite athletes. Knee Surg Sports Traumatol Arthrosc. 2025;34(10):3492-501.
4. Wellsandt E, Failla MJ, Snyder-Mackler L. Limb symmetry indexes can overestimate knee function after anterior cruciate ligament injury. J Orthop Sports Phys Ther. 2017;47(5):334-8.
5. Jordan MJ, Morris N, Nimphius S, Aagaard P, Herzog W. Attenuated lower limb stretch-shorten-cycle capacity in ACL injured vs. non-injured female alpine ski racers: not just a matter of between-limb asymmetry. Front Sports Act Living. 2022;4:853701.
6. Hart CS, Chumanov ES. Investigation of force plate jump testing metrics relevant to return to play decision making in basketball athletes after anterior cruciate ligament reconstruction. Int J Sports Phys Ther. 2025;20(7):985-94.