Strength

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. Sapega (1990)

Imbalance of muscle ratios can be used e.g. shoulder internalrotators 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.

Peak Torque  / Force

The maximal value of the moment angle position (MAP) curve (the peak torque is the highest point on the curve). This is considered to be the gold standard measure in isokinetic testing / exercise (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 over 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 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).

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.

Mean Torque:

Sum of peak torque measured over IROM / number of measurements.

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.

Time peak torque held:

Normally used in isometric testing the amount of time peak torque was held this best demonstrates true isometric strength.

Time to half peak torque:

Isometric reports only this is the time from the beginning of torque development to the point where the torque is half the peak torque. Demonstrates isometric endurance in a more meaningful way.

Peak torque slope:

Used in isometric testing it is the peak torque divided by the time to reach peak torque. Demonstrates how explosive isometrically the contraction.

Force decay time:

Normally used in isometric testing this is the time from the end of peak torque production to the end of the motion. Demonstrates the decay of a tetaniccontraction as such it shows the actualendurance potential of the muscle fibres. 

Average Torque:

Used in isometric testing and normally replaces work. It is the average torque during an isometric contraction.

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. This measure is used mainly where the agonist it stopped by it's antagonistbut each may have a different angle of peak torque. This value can be found in each contraction then the actual ratio can be analysed. For example the shoulder internal rotators concentrically are resisted by the eccentric external rotators. The angle of peak toque of the internalrotators would be used to find the correct angle to look at the peak torque in the eccentric external rotators.

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 neuromuscularfacilitation) show peak torque later in range (for individualranges 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 fibers (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.

Power:

W(ork done) / T(ime taken) = P(ower) Power then is energy divided by time. The unit of power is the watt (W), which is equal to one joule per second.

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.

Contractional Impulse:

Moment (average) x T(ime) = I(mpulse)

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

Reciprocal Delay:

The time required to reverse the limb direction. Another measure of explosive actions this focuses on the ability to change direction rapidly.

Delay time:

The time from the beginning of motion to the beginning of torque development. Used to see if subjects took extra rest with a set between reps.

Acceleration time:

The time taken to accelerate to isokinetic speed.

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.

Deceleration time:

The time taken to decelerate from isokinetic speed back to 0. Only used in concentric contractions as eccentric ones are controlled by the machine.

Coefficient of variation:

The amount of difference between the reps in an individual set. This variable is used to check the consistency of a set the closer the result is to 0 the more consistent the set. In strength tests this should be below 0.20 (Dvir 1995) if the test is to be valid. A high figure is expected in endurance testing. In isometric and isokinetic tests the deviation is worked out from torque whilst in isotonic tests the deviation is from position.

Agonist antagonist ratio:

The peak torque of the weaker muscle group divided by the peak torque of the stronger muscle group then multiplied by 100 to give a percentage. The weaker group is shown as a ratio of the stronger one.