Most knee testing is done in the sitting position.

1 First you need to get the machine to roughly the right place.

Every machine is different but they all have a section in the software (or users manual) that tell you how to get the seat and dynamometer to roughly the right position to test either the right or left knee. It will also tell you which attachments you need to stabilise and fix the subject to the machine.

2 Once in roughly the right position sit your subject on the chair.

TIP: Place two of your fingers between the subjects knee and the chair to make sure they are not too close to the seat with their popliteal vessels. Not can it be uncomfortable if the knee is squashed to the chair it also limits range of motion.

3 Now strap the subject to the chair with the thigh strap (you don't need any other straps).

4 Now align the the axis of rotation.

The axis of rotation goes from the machine (see the blue star below) and extends through the lateral femoral epicondyle (although I believe alignment with the lateral joint line slightly anteriorly to the centre point generally offers better alignment throughout range see below). To check the alignment simply straighten and bend the knee and make sure that the attachment on the calf does not move up and down the shin (this can cause friction burns and does not allow the knee to rotate correctly).

TIP: If you find it hard to set the alignment correctly with the knee bent try doing it with it straight this often helps.

Small errors in alignment can be compensated for by the subject i.e. if you test the alignment and find the subject moves their body in the chair slightly continue to bend and straighten the knee until they stop adjusting and the alignment will be correct.

Here the lateral femoral epicondyle is shown as the red star. The actuator axis (the blue star on the machine and the centre of the lever arm's rotation) should be opposite the later femoral epicondyle or as I prefer the lateral joint line (the blue star on the subject)

5 Position the resistance pad (the bit that straps to the calf) by making sure the bottom of the pad touches the top of the medial malleolus seen as the red star.

6 Set the anatomical zero if the machine requires this (some do and some don't) the anatomical zero is when the knee is straight (this gives the machine  a reference point).

7 Set the range of motion

For flexion try to be between 75-90 degrees of flexion. Then set the range of motion for extension  (personally I would not test beyond 0 degrees extension as an absolute maximum, whilst subjects tend to find limitations beyond 5 degrees of flexion as irritating and tend to do large isometric contractions to try to complete the range).

8 Set gravity correction if you want to!

TIP: The effects of gravity help the hamstrings but hinder the quadriceps, however, if you always test the same person without gravity correction your results will be generally consistent (as long as the subject does not gain or loose allot of weight! Watch out for heavy and light footwear).

9 Set an exercise protocol

We will presume you are going to use isokinetic exercise!

Movement type: Concentric or eccentric? For most subjects a concentric/concentric test will be sufficient. Only move on to eccentric testing if you are interested in a specific muscle or the concentric/concentric results show no problems but you are convinced one exists.

Speed: First you need to choose a speed, generally I recommend a medium joint speed for testing strength. So what is a medium joint speed? Well at any joint a medium speed (in my opinion) is one which gives 1 degree per second for every 1 degree range of motion (what I hear you shout. Think of it like this we have already set a range of motion from 0 degrees extension to say 90 degrees flexion then a medium speed would be 90 degrees per second!). However, in the knee some speeds have been used allot in the research these are 60, 90 and 120 degrees per second for strength and 240, 300 and upwards for endurance. So simply choose one of these speeds to suit your requirements.

Repetitions:

To test strength 3 repetitions should be sufficient (best of 3 as they say). In the real world most subjects don't do well on at least two of these so we are up to 5 repetitions for strength. If you are testing a patient then go for 10 repetitions as they often get better results after 5 but never after 10.

For endurance set a time limit if you can or if you can't a number of repetitions the subject will never complete (you are interested in how long they can carry on for). For time try 5-10 minutes and for reps choose 500 and above.

TIP: Do not use trial repetitions as the machines don't generally record them and you can be guaranteed if you include them your subject will hit peak torque during them. Use more sets instead.

Number of sets: For a strength test one should be enough, but remember we have not used trial reps so we need at least one set to warm up with and get used to the machine and then one set to do the actual test this makes 2 for patients I always use 3 sets (best of 3 to a patient this makes sense). For an endurance test it is one set of 10 to warm up and get familiar with the machine and then just one big long maximal set.

Rest between sets: Always go for 15 to 20 seconds.

10 Start the test!

TIP: remember to get out of the way of the moving limb!

11 Interpretation of results.

First look at the peak torque these figures tell us how strong the subject is and can be compared to the opposite side. If you have tested both sides you should look to see if the sides are within 10 percent of each other (this is a good balance).

TIP: remember there will be two of these figures if you have used concentric/concentric testing there will be on for the quadriceps and one for the hamstrings. If you have used concentric/eccentric testing you will have one results for concentric and one for eccentric.

You may want to look at peak torque to body weight (if it is available). This tells us how strong our subject is compared to their weight and can be compared to the normal values chart shown at the bottom of the page.

Now check the figures which show one half of the test to the other i.e. the concentric/concentric ratio or the concentric/eccentric ratio. In this section you should see that the quadriceps are roughly twice as strong as the hamstrings (a ratio of 200 percent or 50 recent if you compare hamstring to quadriceps). For the concentric/eccentric results you should expect the eccentric value to be 30 percent higher in the quads than the concentric figure. However, in the hamstrings the eccentric figure is usually the same as the concentric figure (in my experience).

Average peak torque (Nm) to body weight (Kg) at 60 degrees/second over a 75 degree ROM (0-75) seated with thigh stabilization.

TIP: If the patient does not have normal muscle strength values then these should be returned using the appropriate isotonic exercises. If this cannot be achieved then isokinetic treatment should be considered using the appropriate protocol.