Irrespective of the joint/muscle system involved there are some basic principles which form a basis for interpretation. These are discussed in a lot of studies but are best described in Sapega (1990).

In the case of testing only one side then the opposite side should be used as a reference (this is not the case in athletes who use one side preferentially over the other e.g. Javelin).

            Imbalance of strength of up to 10% can be considered normal.

            Imbalance between 10 and 20% is possibly abnormal (with Injury this is considered probably abnormal).

            Imbalance of 20% or greater is probably abnormal (in injury this is definitely abnormal).

As a criterion measure for return to activity following injury the following is considered true.

            A maximum of 20% deficit for any individual muscle

           A maximum of 10% deficit for any involved limb (i.e. closed chain testing).

No figures exist that are validated for light activities, but a decrease of 30% for one muscle and 20% for one limb are considered acceptable (bear this in mind when returning patients to driving you could be asked why you did!).

Imbalance of muscle ratios can be used e.g. shoulder internal rotators against external rotators. Try to use the ratios in a meaningful way i.e. the concentric activity of the agonist to the eccentric activity of the antagonist.

In the presence of pathology it is advisable to compare the MAP curve to that of the unaffected side. Care should be taken when using this practice as MAP curve shape is very variable. The separate sections relate specifically to various pathologies and are described best in Chan and Maffulli (1996).

If both limbs are affected or the subject would just like to know how strong they are then comparison to normal values is acceptable please see the normal values section.

Individual Variables

Peak Torque

This is considered to be the gold standard in isokinetic measurement (Kannus 1994). When using peak torque to asses a subject it is appropriate to compare the left side to the right side and look for discrepancies of aver 5% Sapega (1990).

If comparing concentric to eccentric figures (at medium joint speeds) in the same muscle (e.g. Concentric biceps to eccentric biceps) then the eccentric figures should be 30% higher than the concentric figures (Brown 2000), however, this varies from joint to joint and can be as low as 20% or as high as 147% (Brown 2000), and is obviously related to speed (explained below in the force velocity relationship). Individual ratios can be seen in the normal values section. Generally low eccentric figures indicate pathology (Dvir 1995) whilst high eccentric figures can indicate connective tissue disorders (Dvir 1995)

Figures may also be analysed across joints (e.g. Concentric quads to eccentric hamstrings could be important in anterior cruciate ligament deficient subjects as the eccentric hamstrings could in theory resist anterior tibial translation during the concentric pull of the quads) in this situation the closer the eccentric figure to the concentric figure the better (as eccentric muscle action is required to stop a joint motion at the end of range) this comparison is very important in unstable joints like the shoulder (but be aware that the figures can sometimes be misleading as the angle of peak torque will often be different, to accommodate for this the same angles should be used e.g. Torque@angle).

Peak torque can be used to asses the differences in strength between individuals e.g. A 150kg person should be able to produce a higher peak torque than a 80kg person.

The force velocity relationship:

Peak concentric force will decrease with increasing speeds (as long as you start slow and work up in speed), whilst, peak eccentric force will rise initially with increasing speed then plateau and eventually decrease. Using this knowledge it is possible to work out how strong a subject is related to speed and plot this on a graph (known as a force velocity curve). Force velocity curves are used mainly to determine whether an athlete is able to maintain their strength with increasing speed. With this information it is possible to determine whether they need to develop their speed of movement or their strength.

More recently peak torque has been used in 3D muscle mapping along with angle of occurrence and velocity. It has also been used as part of ‘isomap’ in the Biodex system

Mean Torque

This is often used to describe strength and is seen as a less meaningful variable (as fatigue plays a great role in the determination of this figure).

Peak torque to weight ratio

To compare results between individuals peak moment is calculated compared to body weight (either kilos or pounds). Lower limb strength is dependent on body weight and can be expressed in this way. Upper body strength is less dependent and is not usually described this way.

Contractional Work

A measure of the energy expended by the muscle/s under test and considered by some authorities to reflect endurance. However, difficulties in assessing the importance of strength (or lack of) and endurance during the interpretation of these results makes their use questionable for research purposes but good for rehabilitation the higher the work the more the subject has done during each repetition.

Power

Power relates to the average time rate of work. Power does not decline with increasing velocity as peak torque does during concentric contractions instead it increases (Osternig 1986). The use of this measurements is limited mainly because the results can be obtained from the peak torque to time figures. These measurements can highlight differences between elite performers when peak torque figures appear fruitless (Kannus 1994). Power measurements are becoming increasingly popular in the research community to look at performance in activities/sports that are not limited fundamentally be strength.

Acceleration Time

The time it took the machine to accelerate to the preset angular velocity. This will increase with softer stops and higher speeds. If you have tested at high speed the acceleration time required to perform the movement may mean the angle of peak torque is missed (as the figures obtained during the acceleration time are not included as this portion of the movement is considered to be isotonic and is usually damped) so it is important to ensure the range of motion is large enough to accommodate for this. If tests are performed at many different speeds then the angle of peak torque should remain in the same place if the range of motion is sufficient, if not the peak torque figures may be worthless.

Angle specific torque

Used to determine a specific angle torque relationship which may be of interest (for instance when looking at agonist/antagonist con/ecc ratios). It has been shown (Kannus and Kaplan 1991) to be most reliable in middle joint ranges with decreasing reliability at the extremes of motion.

Angle of peak torque

As the name suggests (but often called angle of occurrence) this is when peak torque reaches it’s maximum level. It can be useful as an indicator of maximum torque production if plotted against various velocities (Osternig 1986). Weaker muscles (probably due to neuromuscular facilitation) show peak torque later in range (for individual ranges see individual joints) as has been demonstrated by Kannus and Jarvien (1990). The reliability of this measure is often very low (Kannus 1994) and is made worse by repeated tests (due to alignment problems, Chan and Maffulli 1996)

Time to peak torque

Evaluates the ability to produce force rapidly and can be used to determine explosive power. A prolonged time to peak torque can indicate reduced recruitment of type II fibres (Kannus 1994). This has been superseded by peak torque acceleration energy.

Peak torque acceleration energy

Amount of work performed in the first 125 ms of a torque production cycle. This is supposed to reflect explosive power as it assesses the speed and rate of torque production. As an accurate measure it is very variable at slow speeds (Kannus 1994) and can be greatly affected by exercise cycles i.e. if there is no pause between con/ecc cycle then the results are usually useless. Ecc/ecc and con/con exercises produce best results, however, even these have been questioned as they may not (according to Perrin et al 1989) have a basis in Newtonian physics.

Contractional Impulse

Used in literature to describe the difference in performance where the peak torque reveals no differences.

Coefficient of Variance

This describes the consistency of the results obtained. At the moment this type of testing has gained a lot of support. It is used in a lot of back testing systems but it has NEVER been tested in court. If the results are low then the repetitions are closely matched to each other (in other worlds a COV of 0 would mean each rep was the same). High results could suggest the subject needs more practice. High results are often used to diagnose psycho/musculskeletal problems. A High figure is expected during an endurance test.

Declined Work

The most widely used endurance measure. The amount of work performed over a set number of repetitions is recorded. These tests have been said to be absolute endurance measures which should be used in research settings (Kannus 1994). The trouble starts when subjects can not reach the set number of repetitions required.

Time to 50% of peak torque.

This is the amount of time the subject can maintain a repetitive peak moment level of 50% (or any other figure you decide 50% is common in the literature) above the peak moment obtained at the initial contraction. This type of testing eliminates the problem of failure to reach repetitions but it is easily cheated if the subject fails to exert maximally during the first repetition.

Endurance Ratio

The peak torque of the first X number of repetitions (usually 5) divided by the peak torque of the last X number of repetitions (usually 5) multiplied by 100 to give a percentage.

In reality the line of least squares fit is used for the first 5 reps. This is divided by the line of least squares fit for the last 5 reps X by 100.

Any figure under 100 means the subject fatigued (the lower the figure the more the fatigue e.g. a fatigue ratio of 65% means the subject tired by 35% during the test).

A figure over 100 means the test went wrong!