Glossary

Isokinetic strength testing

Quick answer

Isokinetic strength testing uses a computerised machine to measure the strength of the quadriceps and hamstrings at a fixed speed, comparing the injured leg with the healthy one. It shows strength deficits that are hard to spot by eye and guides rehabilitation and return to sport, explains Doha knee surgeon Dr. Pablo Gelber at Aman Hospital.

What the test feels like

You sit in a chair attached to a dynamometer, with straps across the thigh and waist and a pad fastened just above the ankle. After a warm-up, you kick out and pull back as hard as you can through a set range, several times, at one or more speeds. The machine controls the speed, so it resists however hard you push.

It is a maximal effort test, and your thigh will feel tired afterwards. It is done only when the knee is ready and is stopped if there is pain.

What it tells the surgeon

The machine produces curves and numbers for each leg, including peak force. The main result is the percentage difference between legs. After ACL reconstruction, quadriceps weakness is common and can last many months, and it is linked to poorer function and a higher risk of re-injury.

The hamstring-to-quadriceps ratio also gives information on muscle balance. Results help the physiotherapist target training, and together with hop tests and questionnaires they help the surgeon judge when a return to football, padel or other pivoting sport is reasonable.

Frequently asked questions

Is isokinetic testing safe after knee surgery?

Yes, when done at the right stage and supervised. The range and speed can be adjusted to protect a healing graft or repair.

Why test on a machine if I feel strong?

Feeling strong and being equally strong are different. The machine often shows a deficit that is not obvious in daily activity but matters in sport.