Flexion / Extension

The most stabilised position for testing extension and flexion but it limits flexion unless the subject can get very close to the edge of the seat. Best overall position.

Seated testing assumes that minimal femoral motion will occur as the chair and body act as distal stabilisers of the thigh.

The subject usually sits with their back and thighs supported making approximately a right angle at the hip.

The thigh support should extend to allow the appropriate amount of knee flexion. Try to leave two fingers gap between the chair and the back of the calf. In most tests this would be somewhere towards the distal third of the thigh which would allow 75-90 degrees of flexion (the maximum knee flexion available is approximately 110 degrees whilst retaining reproducibility).

This position then allows maximal extension (although debate rages over whether extension beyond -20 degrees should be permitted. Do not test beyond 0 degrees extension as an absolute maximum, subjects tend to find limitations beyond 5 degrees irritating and tend to do large isometric contractions to try to complete the range so try to stick to 0 degrees if possible. Although the angle of seat recline (from the semi-reclined to the upright position, i.e. 40-90 degrees), has little effect on quadriceps strength it has significant effects on hamstring strength. The optimal position is approximately 80 degrees (with a corresponding change in seat angle recline to give 90 degrees at the hips). This optimal position is suggested for both extensors and flexors as it allows the collection of good data over the least time.

To view a set up video see below

Standing position:

In the standing position stabilization is difficult if not impossible (and probably undesirable). Testing in this position is more functional than that in the seated position.

Prone lying position:

Prone allows for a much broader range of motion to be assessed. This position is generally used if the hamstring muscles are of particular interest (as stabilization of the knee flexion movement is easily achieved in this position). Stabilization is accomplished by allowing the subject to hold the seat edges and a femoral and waist strap should be applied. On the Cybex norm the seat does not lock into the down position this means that as the subject works the seat will raise up and crash back down. This can be prevented in the short term by wrapping the waist belt around both the patient and the chair. This appears to be an oversight on this machine. Best for hamstring tests.

The subject is prone and the thigh support extends to allow the knee to be off the edge of the seat. The seat can be seen as the red line whilst the blue stars represent the joint line.

To view a set up video press here 

Supine lying position:

Supine allows for the focus of the test to be on rectus-femoris. In essence it is the same as seated but with the chair made into a bed. This is the least used position. Supine testing assumes that minimal pelvic and femoral rotation will occur will occur as the chair and body act as distal stabilizers of the thigh, however, the subject will often shift the pelvis (hip hitching) to gain a better leaver advantage. 90 degrees  of knee flexion is needed in this position so you can obtain the peak torque measurement at the optimal angle of peak torque for the rectus femoris.

Stabilisation:

Seated: Stabilization is normally accomplished using femoral and pelvic strapping, however, the optimal set-up is a bit more involved. The number of research papers available on the subject is incredible. Magnusson et al (1992) showed that stabilization with a thoracic strap and the hands was associated with the highest quadriceps strength whilst no stabilization produced the lowest score. Hart et al (1984) also showed the use of a thoracic strap to improve quadriceps strength, whilst Hanton and Ramberg (1988) found exactly the opposite. Use of a thoracic, pelvic and femoral strap decreased quadriceps strength when compared to minimal stabilization i.e. only gripping the sides of the testing table.

Interestingly, Currier (1977) whilst testing isometric strength found that gripping of the table increased strength whilst gripping of handles did not show such significant improvements. These results were elaborated upon by Bohannon (1986) when he tested various gripping devices compared to only gripping the table and found massive differences. Hence, most isokinetic dynamometers do not offer hand grips as an option.

Prone Lying: Stabilization is normally accomplished using femoral and pelvic strapping and the subject is allowed to hold the chair or the handles provided.

Standing: Stabilization is almost impossible and  would be undesirable as this position is the most functional.

Supine: Is normally accomplished using femoral and pelvic strapping and the subject is allowed to hold the chair or the handles provided.

Attachments:

Whilst testing normal subjects the resistance pad is placed on a level with the inferior part of the pad immediately superior to the medial malleolus shown here (in other words the bottom of the pad touches the top of the medial malleolus). This is because 70% of all subjects tested by Kramer et al (1989) found this the most comfortable with the other 30% preferring a position at two-thirds of the usable leg length (after you have spent an hour determining the usable leg length and then calculating a position two-thirds down this, your subject will be so fed up the results will be negated by poor subject motivation).

When using any selected location the subject should be free to maximally dorsiflex the foot (as seen below). 

Close attention should be paid to not over tightening the strap around the shank as the resistance pad will, in all subjects, slide up and down the leg to some degree (this is because of the change in joint axis through range).

Consistency in the position of the resistance pads is, therefore, crucial.

Axis of rotation:

Setting up the machine to get the subject in roughly the right position is only the first part of the task. Do not be afraid to move the seat or dynamometer to allow for better alignment of the biological axis of rotation. At the knee this changes throughout range (so we use a compromise position). Dvir (1995) tells us this extends through the lateral femoral epicondyle (although 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).