Definitions

Posted on 31 July, 2013

Muscle Action

Muscle action is the term more favoured than ‘contraction’ to describe the active state of muscle. It describes the attempt by muscle to form cross-bridges, generate tension and shorten.

Concentric muscle action

Shortening of the contractile component occurs as cross-bridges are formed and tension is generated.
Tension is transmitted to the SEC. The SEC becomes stretched until the tension in the SEC approximates the tension in the contractile component (CC).
No movement occurs until the muscle torque exceeds the resistive torque.
A decrease in the distance between the muscle attachments occurs.

Eccentric muscle action

Shortening of the contractile component occurs as cross-bridges are formed and tension is generated.
Tension is transmitted to the SEC. The SEC becomes stretched until the tension in the SEC approximates the tension in the CC.
The muscle torque remains less than the resistive (load) torque.
An increase in the distance between the muscle attachments occurs.

Isokinetic exercise mode

The resistive torque equals the applied (muscle) torque and therefore constant angular velocity concentric or eccentric muscle actions occur.

Isokinetic strength

The torque produced by a muscle group in a maximal muscle action (concentric and/or eccentric) through a specified range of movement at a constant angular velocity of movement. As angular velocity is constrained, torque is the variable which changes.

Anatomical Referencing

Referencing the Kin-Com machine angle to the subject’s joint angle and anatomical range of motion.

Gravity Correction

Gravity correction is the procedure by which the torque due to the limb(s) or segment(s) are accounted for. Failing to institute gravity correction procedures on the raw data will:

change the shape of the strength curve
underestimate the true muscle torque of a muscle group working against gravity, or
overestimate the true muscle torque of a muscle group working with gravity, thereby
changing muscle balance ratios.

Preload

Preloading is the process by which an isometric muscle action precedes the movement phase. The muscle has time (without movement) to generate high levels of torque. Brief acceleration times may provide for a greater isokinetic range of movement and a ‘truer’ strength curve.

Full range average torque – FRAT

The FRAT is calculated as the default measure of strength in the Kin-Com reports when torque is the unit of measurement and the markers are located at the ends of the curves. The software averages all torque values between the markers.

Truncated range average torque – TRAT

The TRAT can be calculated as a measure of strength (my preferred measure!) in the Kin-Com reports when torque is the unit of measurement and the markers are moved in from the ends of range by an amount which at least removes the accelerative and decelerative phases of movement. The software averages all torque values between the markers and results in an average torque specific to the isokinetic range of movement. If performing a multiple velocity assessment, it is important to calculate the average torques over the same range of movement. This means that the least isokinetic range of motion is used (i.e. the IROM for the greatest velocity) for all velocities and muscle actions.

Peak torque – PT

Peak torque is the maximum torque value which occurs in the range of movement. It may only be approximated during isometric testing but is usually able to be measured during constant angular velocity movement. When a muscle functions normally the peak torque can reasonably be expected to occur with only a small variation about a known joint angle or muscle length. Research has not yet confirmed that peak torque occurs at the same joint angle when velocity is varied, or when concentric and eccentric isokinetic muscle actions are compared. There may be occasions where factors such as reduced joint range, pain or stretch weakness result in some variation in the angle at which peak torque is attained. A major concern with the using peak torque as a measure of strength is that some muscle groups do not have a true peak, simply a transitory peak for the range of movement tested. For this reason alone, average torque is preferred, although the range over which average torque is calculated should be specified.

Angle specific torque – AST

Angle-specific torque is the torque value at a specified angle or position in the range of movement. This is also referred to as constant-angle torque (Hortobagyi & Katch, 1990) and angle-based moment (Dvir, 1995).

Work – W

Work can be calculated as a measure of strength in the Kin-Com Standard Report when torque is the unit of measurement. Again, my preference would be to move the markers in from the ends of range by an amount which at least removes the accelerative and decelerative phases of movement. The software calculates the area beneath the curve and between the markers, and determines a work value specific to the isokinetic range of movement. If performing a multiple velocity assessment, it is important to calculate the work values over the same range of movement. This means that the least isokinetic range of motion is used (i.e. the IROM for the greatest velocity) for all velocities and muscle actions. Work is a very similar measure to average torque and should correlate exactly with average torque when the ROM is the same.

Average power – AP

Average power is not presently calculated in the Kin-Com software (other that the Kin-Com I software) although it may be argued that is an important measure of strength. It is not widely sued and this is probably because of the historical use of torque measures. Again, it is related to average torque by the laws of physics, being the product of torque and angular velocity, or work divided by time.

Range of motion – ROM

The range of motion is the angular displacement between the start and stop angles. As such it includes the phases of movement when the lever arm speeds up (accelerates), maintains constant speed (isokinetic), and slows down (decelerates).

Isokinetic range of motion – IROM

The isokinetic range of motion is determined by subtracting the range of movement where the Kin-Com accelerates to the pre-set velocity and decelerates from the pre-set velocity. The movement through the ROM between these accelerative and decelerative phases should be at constant angular velocity or at the isokinetic velocity, hence the IROM.

Kin-Com Analysis Package – KCAP

KCAP is a computer program written in MPW C for the Macintosh. A PC floppy disk with a copy of a Kin-Com ‘datafile.CHA’ or ‘datafile.CHT’ is placed in a Macintosh floppy disk drive. These drives will read the PC disk. The KCAP program then imports the datafile and saves it as a Macintosh binary file. This new file is then opened and various data analysis and graphical displays are selected. In particular, KCAP calculates work and power measures of strength for data saved in both overlay (.CHA) and continuous (.CHT) files. The range of data and graphical displays for the isometric and isotonic exercise modes are particularly enhanced.

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