In most modern systems based on either a resistance pad and a load sensor (where the position of the lever arm is adjustable like the Kin-Com AP) or where torque is derived from turning force at the actuator axis (like in the Cybex Norm, Biodex multi joint system 3, Isocom and Isomed), the following is true:-

Torque

The turning effect (moment) of a force on an object. Torque = moment x distance from turning centre (in this case the centre of rotation of the lever arm).

Peak Torque

The maximal value of the MAP curve (see Acc/Deceleration curves as these are both MAP curves, the peak torque is the highest point on the curve). This is considered to be the gold standard in isokinetic measurement (Kannus 1994).

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.

Contractional Work

W(ork) = torque x angular displacement

Total work (TW) = Area under torque curve x angular displacement (according to Hislop and Perrine 1967)

Peak power (PP) = work done during the best repetition (often called best work repetition BWR)

All described in J(oules)

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.

Power

W(ork done) / T(ime taken) = P(ower)

Usually measured in Watts

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)

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 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.

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.

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% 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.

Reductions in peak torque.

There are many different tests to look at how much torque, work or power decrease over a set number of repetitions. The variations are staggering.