Our lecture today to focus on the use of Cybex II for the measurement.
Many isokinetic devices are used to evaluate and measure muscle performance. Cybex is one of these devices provide isokinetic loading (with constant velocity).
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 subjects 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.
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.
A hydraulic load cell within the machine measures the torque ( the angular analog of force) needed to keep the limb from accelerating beyond the machines pre- set speed.
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.
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.
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 machines set speed there will be no torque recorded. The Cybex II records only the resistive force needed to keep the limb from accelerating.
Moffroid et al examine the reliability of the Cybex I by attaching weights (60, 57, 40, 30, 20, 10, and 5 lbs) to the machines lever arm. Ten test-retest sessions using the loads produced a coefficient of reliability of r=.995
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.
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.
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
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.
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 Validity Isokinetic 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 ( 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
procedures Any isokinetic test (including the initial test) or exercise should include the following : WarmUp Before starting the test or exercise, the patient should engage in a short cardiovascular warmup 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 warmups on the unit. RecordKeeping Throughout the program, the clinician should consistently record: Pertinent patient information on pain, progress, range of motion, endurance and other factors. Stabilization and setup 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 patients: 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.