Isokinetic devicesLecture IV

Isokinetic devicesCybex

Our lecture today to focus on the use of Cybex II for the measurement.

Introduction

Many isokinetic devices are used to evaluate and measure muscle performance.

Cybex is one of these devices provide isokinetic loading (with constant velocity).

Introduction

Machine Cybex

The Cybex II consists of a movable lever arm controlled by an electronic servomotor that can be set for angular velocities from 0◦ to 300◦ per second. The lever arm is attached to a subject’s limb and the subject is then asked to move as fast as possible. The machine is designed to maintain limb movement at a constant angular velocity and provide accommodating resistance.

The torque is registered on a strip- chart recording. The dynamometers are interfaced with computers that provide

many different measures of muscle performance, such as peak torque, torque to body weight ratios, endurance factors, and torque measurements at certain ranges of motion.

In addition, all of these measures can be taken at different speeds. Some of the machines allow testing of eccentric as well as concentric muscle contractions.

Fundamentals

Active Dynamometer  This is within the head assembly and controls the machines speed by altering the force .

     The Seat

The Control Unit

THE FORCE ACCEPTANCE UNIT

This is the big unit which the patient will move a part of .

The lever arm

The load cell

The Head Assembly

This houses the motor (active dynamometer) and is responsible for controlling the lever arm.

Specific Attachments

These are used to attach the subject to the machine.

Isocom

Cybex II

When the subject attempts to accelerate beyond the pre-set machine speed, the machine resist the movement.

The machine is designed to maintain limb movement at a constant angular velocity and provide accommodating resistance.

Cybex II

A hydraulic load cell within the machine measures the torque ( the angular analog of force) needed to keep the limb from accelerating beyond the machine’s pre-set speed.

Cybex II

Torque measurement by attach the limb to the Cybex, the axis of rotation for the limb must be aligned with the mechanical axis of the machine, so the lever arm of the limb and the machine are equal and the distance from the axis does not have to be measured and used in calculations.

Cybex II

Recently, a Cybex computer has been provides a digital printout, modifies data, and permits measurements of other variables as power and work.

torque measurement by Cybex is the easiest way.

Cybex II

Torque measurements are ratio scale because a zero indicates an absence of the quantity being measured, but if the limb moves at a speed slower than the machine’s set speed there will be no torque recorded.

The Cybex II records only the resistive force needed to keep the limb from accelerating.

Cybex II

http://www.ied.edu.hk/pe/VIDEO/hplBA.MOV

Moffroid et al examine the reliability of the Cybex I by attaching weights (60, 57, 40, 30, 20, 10, and 5 lbs) to the machine’s lever arm.

Ten test-retest sessions using the loads produced a coefficient of reliability of r= .995

Reliability

The authors did not appear how this statistic was calculated.

The isokinetic movements was not tested because the procedure assessed the reliability of the device for the static measurement of weight.

The study did not involve people (stability, motivation, subject comfort and axis alignment).

Reliability cannot be generalized from weights to people.

Weaknesses of the Study

Johnson and Siegel examined whether a Cybex II could reliable measure knee extensors peak torque in 40 healthy women (ranging in age from 17 to 50 years).

Subjects were tested at 180˚per second on six consecutive days.

On each occasion, subjects were allowed three sub-maximal warm-up contractions followed by six maximal contractions.

The authors determined that reliability was best when the mean of last three contractions were used.

Reliability of Cybex II

Johnson and Siegal study represent the most carefully designed and fully documented investigation into the reliability of Cybex II.

1- healthy subjects were tested 2- one speed was examined 3- only knee extension was tested 4- A precise protocol was used 5- movement was tested in one direction 6- mean data were used

Reliability of Cybex II

Mawdsley and Knapik in a study of knee extensor peak torque at 30° per second. Sixteen subjects (12 men and four women ranging in age from 20 to 50 years) were tested with the Cybex II on three occasions with a two-week interval between sessions. 1-The authors concluded; measurements did not change significantly over the six-week period .

2- only one maximal warmup contraction is needed to ensure reliable measurements.

Reliability of Cybex II

Validity Criterion Referenced Validity: Concurrent Validity.

Gerdl et al. (1986) found a strong correlation between isokinetic endurance testing during repeated plantarflexion contractions and the maximal functional walking capacity in patients with peripheral arterial insufficiency and intermittent claudication. That means if a patient has a low score on this endurance test their walking capacity will be correspondingly limited (this test may be more suitable as it involves less risk to the patient).Pain sensation scores during knee testing have a high correlation with PF pain syndrome, particularly at lower test angular velocities. If after therapeutic intervention slower tests give less pain then this could be a measurable outcome .

Validity

Content ValidityIsokinetic dynamometry has content validity with respect to specific aspects of muscle performance. As velocity increases force generation decreases but average power increases (Fugl-Meyer et al. 1982) .

Predictive Validity .

Knapik et al. (1981) found in season injury rates higher in women if they had knee flexors 15% (or more) stronger than the contralateral side at 180 degrees/second .

Factors effect the measurement Gender. Age. Activity Level. Body weight. Muscle characteristics.

Contraindication

Soft tissue healing constraints :Non united fractures to limb ,Recent surgery, Skin problems under load cell

Epilepsy Cardiac insufficiency (unless monitored) Severe peripheral vascular disease Anticoagulants Malignancy (in area to be tested) Recent (< 3 months prev) X-ray/chemo therapy Long term steroid use (> 3 months) Acute (< 7 days) muscle/ligament tear (>grade I) Pregnancy Any neurological condition (e.g. stroke, Parkinson's disease) unless closely

monitored Severe osteoporosis Sever pain Unstable joint Extremely limited rang of motion Sever joint effusion Limited range of motion (severe)

Disadvantages

Cost,expensive devices/machines Isokinetic dynamometers are more favorable for the hip,

knee, and ankle joints Devices are large Misunderstanding in the usage lacking education of user Machine Linked Inconsistencies

There are 3 main problems with isokinetic test results for different models or systems.     Differences between individual machines of the same

model type (software especially)     Differences between tests on the same machine during

normal operation     Different models or systems

Measurement

proceduresAny isokinetic test (including the initial test) or exercise should include the following :

Warm—Up Before starting the test or exercise, the patient should engage in a short cardiovascular warm—up to raise muscle temperature (e.g. using a UBE or Fitron.) Prior to the actual session, the patient should actively stretch the muscles which will be involved in the test. Prior to each speed set, the patient should perform submaximal and maximal effort warm—ups on the unit.

Record—Keeping Throughout the program, the clinician should consistently record: Pertinent patient information on pain, progress, range of motion, endurance and other factors. Stabilization and set—up information. Body weight and, if possible, percent fat changes.Other pertinent data to insure accurate records and consistent test administration.

procedures

Precautions Subjects should be monitored closely for signs of distress during any testing or exercise session. The clinician should pay close attention to the patient’s: •Vital Signs — Monitor blood pressure and heart rate, before and after the session. •Color — in response to exertion. •Quality of movement. •Degree of motivation and effort. •Pain rating.

Hip

Saggital Plane MotionFrontal Plane Motions

Ankle

Testing of Inversion and EversionDorsiflexion and Plantarflexion

Elbow

Flexion/ExtensionRadial & Ulna Deviation  

Wrist

Radial & Ulna Deviation

 Flexion/Extension

 

Knee

Shoulder

Abduction/AdductionInternal/External RotationsFlexion/Extension

Recording

Cybex Multi-session