Isokinetics in Rehabilitation
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Dr. Reza Mazaheri M.D.
Tehran university of medical science
ISOKINETIC EXERCISE
The concept of isokinetic exercise was described in 1967
by Hislop and Perrine.
Isokinetic exercise can best be described as
Ø Movement that occurs at a constant angular velocity with
accommodating resistance.
Then maximum muscle tension can be generated
throughout the range of motion because
Ø The resistance is variable to match the muscle tension produced
at the various points in the range of motion.
Isokinetic machines allow the angular velocity to
be preset.
Once the specified angular velocity is achieved,
Ø The machine provides accommodating resistance
throughout the specified range of motion.
Isokinetic evaluation and rehabilitation are
limited by
Ø The technological advances of isokinetic
dynamometers.
Isokinetic dynamometers now provide concentric and
eccentric resistance.
Velocities are variable depending on the machine,
although
Ø The average range is from zero to 300 degrees/second in the
eccentric mode.
Ø Some machines allow concentric velocities greater than 500
degrees/second.
Historically, the two primary advantages associated with
isokinetic exercise are
Ø The ability to work maximally throughout the range of motion and
Ø The ability to work at various velocities to simulate functional
activity.
Velocities achieved during functional activity greatly exceed
the velocity capacities of isokinetic dynamometers.
Angular velocities produced by professional baseball pitchers
have been shown to range between 6,500 and 7,200
degrees/second.
Velocities measured at the hip and knee during a soccer kick
exceeded 400 degrees/second and 1,200 degrees/second,
respectively.
The majority of isokinetic testing is done in a non-weightbearing position that is not representative of functional
activities.
It is important to remember that many variables contribute to
overall athletic performance.
ISOKINETIC DYNAMOMETERS
Various isokinetic dynamometers are
commercially available to the athletic trainer.
The different systems all offer variable types of
resistance and velocities.
Biodex
The Biodex System 3
isokinetic dynamometer
allows
Ø Concentric and
Ø Eccentric motion.
This system has isometric, isotonic, CPM and
isokinetic exercise modes.
Concentric velocities range from 30 to 500
degrees/second.
Eccentric velocities range from 10 to 300
degrees/second.
Maximum torque values allowed for safety
purposes are
Ø 500 ft lb concentrically and
Ø 300 ft lb eccentrically.
Advantages
One advantage of the Biodex is that
Ø It allows for high-speed concentric activity while being fairly user
friendly.
The Biodex also can be set up easily for strengthening in diagonal
planes.
The Biodex generates a very comprehensive report after isokinetic
evaluation.
Another advantage is that, as just mentioned,
Ø It is the only dynamometer currently in production.
The Biodex does have a lower eccentric maximum, which may be a
limitation when used in the athletic population.
Cybex 6000
The Cybex 6000
allows
Ø Concentric and
Ø Eccentric motion.
The Cybex 6000 has powered and non-powered modes.
The non-powered mode allows free limb acceleration
with concentric/concentric activity that is similar to
previous Cybex dynamometers.
The powered mode provides both concentric and
eccentric activity and continuous passive motion (CPM).
The Cybex 6000 has 18 exercise/test patterns available.
Non-powered concentric velocities range from 15 to 500
degrees/second.
The torque maximum for non-powered concentric activity
is 500 ft lb.
Powered concentric velocities range from 15 to 300
degrees/second.
The torque maximum for this mode is also 500 ft lb.
Powered eccentric velocities range from 15 to 300
degrees/second.
The torque maximums vary depending on the velocity in
eccentric mode.
Ø The torque maximum for velocities between 15 and 55
degrees/second is 250 ft lb.
Ø The torque maximum in the eccentric powered mode for
velocities between 60 and 300 degrees/second is 300 ft lb.
The velocities in the continuous passive motion mode
vary between 1 and 300 degrees/second.
One of the primary advantages of this dynamometer is that it is a
Cybex product.
The non-powered mode of this dynamometer is the same as
previous Cybex dynamometer, so
Ø The normative and research data can be used as comparison data with
this machine.
This machine also is very versatile in that it can be used for many
exercise patterns for the upper and lower extremity.
Cybex has increased its speeds in the powered concentric and
eccentric mode.
The non-powered mode has the highest velocities and torque
maximums available.
The disadvantage of the Cybex is similar to that of the Biodex, with
lower eccentric torque maximums velocities when used in the
athletic population.
Kin-Com
The Kin-Com isokinetic
dynamometer was the first
active system available that
allowed
Ø Concentric and
Ø Eccentric activity.
The Kin-Com has options for a dual-channel EMG
system to use in combination with the Kin-Com.
The Kin-Com dynamometers offer isometric, isotonic,
continuous passive motion (CPM), and isokinetic modes.
The velocities for isotonic, CPM, and isokinetic
(concentric and eccentric) modes
Ø Range from 1 to 250 degrees/second.
The force maximums are 450 ft Ib (2000 Newtons) for all
of the exercise modes.
All of the Kin-Com dynamometers are computer
controlled.
The Kin-Com dynamometers offer the highest force
maximums combined with high velocities for eccentric
testing and rehabilitation,
which is a distinct advantage in the athletic setting.
The Kin-Com does not provide as comprehensive a data
report as other dynamometers.
The Kin-Com is limited to 250 degrees/second in the
concentric mode,
Ø Which is slower than other available isokinetic dynamometers.
ISOKINETIC EVALUATION
Parameters
Various parameters of force and torque are used to
compare extremities during isokinetic evaluation.
Primarily, force or torque data are used in isokinetic
literature.
Force can best be described as
Ø The push or pull produced by the action of one object on
another.
Force is measured in pounds or Newtons.
Torque is
Ø The moment of force applied during rotational motion.
Torque is measured in foot-pounds or Newtonmeters.
Most of the isokinetic dynamometers use torque
as the measured parameter.
The force and torque parameters in the literature
relate to either
Ø Peak or
Ø Average
force-torque production.
Peak force/torque is the point of highest force/torque
production.
Average forcer-torque is the force/torque produced
across the whole range of motion.
Peak and average force/torque can also be compared to
body weight for a weight-adjusted force/torque.
Work and power parameters are also identified in
isokinetic literature.
Work is defined as force multiplied by displacement.
Work is best represented as the area under the torque or
force curve.
Power is defined as the rate of performing work.
Data relating to power characteristics are best
evaluated by
Ø Identifying the amount of work performed in a specific
time period.
Endurance parameters are also evaluated in
relationship to
Ø Reductions in peak torque from the first repetition to
the last repetition.
Another parameter that may be evaluated is
Ø The time it takes to drop to 50 percent of peak torque.
Testing
Isokinetic evaluation is dependent on many different variables to
produce a reliable test.
Two of the variables are speed of testing and the position of the
athlete during testing.
These variables need to be controlled and should be consistent from
test session to test session.
The athletic trainer needs to test the athlete at specific speeds if
comparison to normative data is desired.
The literature provides a vast array of testing speeds for upper- and
lower-extremity isokinetic evaluations.
Previous research suggested that
Ø Testing at different speeds allowed the sports
therapist to test different characteristics of muscular
strength and power.
The current research supports the view that
torque, work, and power characteristics are
determined independent of test velocity.
The results are not indicative of the ability of the
individual muscle to perform different strength or
power tasks.
Generally, 60 degrees/second has been used as the primary test speed for
concentric isokinetic testing.
Eccentric testing speeds tend to be more variable.
Hageman and Sorenson recommend
Ø 150 degrees/second as the upper limit for eccentric testing in the general
population and
Ø 180 degrees/second as the upper limit in the athletic population.
Coactivation of the antagonistic musculature occurs with faster speed testing.
This coactivation happens because
Ø The antagonistic musculature produces force to slow down the lever arm in
preparation for the end point of the range of motion with open kinetic testing.
This coactivation most probably occurs in the non-powered mode of
isokinetic testing because of free acceleration of the lever arm.
No resistance is applied until the subject meets the preset velocity.
This is the most probable cause of increased antagonistic activity to slow
down the lever arm.
The powered mode entails the use of a preload.
This necessitates the production of a predetermined amount of force
before isokinetic contraction can be initiated, eliminating the free
acceleration of the lever arm.
This is one variable that can affect accurate isokinetic assessment.
(mode).
The other is pain inhibition-a protective neuromuscular response of
an involved muscle to limit maximal recruitment of muscle fibers
secondary to pain and swelling.
Pain inhibition can lead to variations in torque production from one
testing session to another.
To limit this effect, testing should be performed when the injured
body part is not effused or swollen.
Positioning of the joint should account for the gravity
effect and the healing phase of the injured structures.
The gravity effect torque must be calculated if the
athletic trainer is analyzing reciprocal group ratios such
as the quadriceps and hamstrings.
An easy way to control this effect is to
Ø Test the different muscles in different positions
so that each muscle is in an antigravity position during
testing.
Many of the new dynamometers correct for the gravity
effect torque if desired.
Positioning the tested joint so that it reproduces functional
activity can be beneficial for the athletic trainer.
The effect of hip position on the torque values of the
quadriceps and hamstrings has been studied by Worrell et al.
Their results indicated that peak torque was greater in the
seated position and less in the supine position.
However, the authors state that evaluation of peak torque
might be more appropriate from the supine position to mimic
hip position during functional activity.
The length of the lever arm of the dynamometer affects
Ø The ability to produce torque.
Torque production is significantly affected when
Ø The lever arm is changed in length.
The athletic trainer can limit torque production early in
the healing phase of injury by
Ø Decreasing the length of the lever arm.
However, the length of the lever arm needs to be
consistent between testing sessions if
Ø The athletic trainer is comparing previous testing sessions to the
current test.
Reliability
In Isokinetic Exercise and
Assessment,
Perrin recommends
Ø A specific protocol for
isokinetic testing.
It is important that the athletic trainer have reliable and reproducible
test results.
Test reliability is dependent on many factors but is probably the
most overlooked aspect of isokinetic evaluation.
Because of the wide variety of test protocols in the literature, the
clinician should include several essential components within the
isokinetic test to facilitate reliability of measurement.
The clinician needs to evaluate the use of a warm-up period and a
rest period, the number of test repetitions, and test velocity.
The recommended rest period between different test velocities is 60
seconds.
These variables need to be consistent between testing sessions for
comparison data as well as facilitating maximal torque production.
Kues recommends that patients have two practice sessions prior to the actual
test.
Reliability can also be influenced by the testing mode.
Eccentric testing especially involves a significant learning curve because of
Ø The athlete's unfamiliarity with this exercise mode, but test-retest reliability in this
mode has been established.
Testing of multiaxial joints, such as the shoulder and ankle, can make it
difficult to reproduce test results secondary to
Ø The complexity of setups, as well as
Ø The limitations in aligning the axis of rotation of the Limb with the mechanical axis of
rotation of the machine.
Results have shown very poor reliability between repetitive trials of peak
torque for ankle plantarflexion/dorsiflexion.
A suggestion to limit the error is to always test both extremities during a testing
session.
The athletic trainer should limit comparisons between testing sessions.
Broad statements regarding the strength and functional ability of the
tested musculature should be limited, because
Ø Isokinetic evaluation may not be correlated with the ability to perform
functional activity.
However, retesting of the involved musculature does enable the
athletic trainer to evaluate the effectiveness of the rehabilitation
program.
Improvements in test results that occur within 1 week of testing
probably
Ø Do not reflect changes in strength of the involved musculature but
are indicative of either the athlete's familiarity with testing or possibly
neuromuscular changes within the muscle.
True strength changes involving hypertrophic changes in the muscle
usually require 4 to 6 weeks of training.
Interpretation of Graphs
Specific ratios of force, torque, work, or power are identified during
isokinetic testing to determine differences between the two tested
extremities.
The most commonly used ratios are peak/average torque ratios
between injured/non-injured extremities, agonist/antagonist ratios,
and concentric/eccentric ratios.
Historically, normal peak and average force/torque ratios comparing
the injured to the uninjured extremity typically use the 85 to 90
percent ratio to allow the athlete to return to competition.
However, the athletic trainer should not use a percentage criterion
as the sole indicator for return to activity, Because
Ø Functional activity has many variables that need to be present for
optimal sports performance.
The hamstring/quadriceps ratio is the most analyzed
ratio.
Historically, based on Cybex evaluations, a 66 percent
ratio between the hamstrings and the quadriceps at 60
degrees/second is described as the normative value.
This testing is only done in the concentric mode.
It is very important for athletic trainers to compare their
results with research that was performed in the same
manner with respect to
Ø gravity correction,
Ø velocity, and
Ø activity status.
Finally, the eccentric/concentric ratio is another
parameter to evaluate with isokinetic testing.
Blacker reports that eccentric testing should produce a 5
to 70 percent increase in force/torque as compared with
concentric testing.
Bennett and Stauber identified eccentric to concentric
quadriceps torque deficits in approximately 30 percent of
their patients with anterior knee pain.
The deficit was defined as less than an 85 percent peak
torque ratio between eccentric and concentric activity.
The symptoms and isokinetic deficits were reversed
through a training program.
Trudelle-Jackson et al, however, tested
asymptomatic subjects concentrically and
eccentrically and reported
Ø A significant percentage of healthy subjects who
demonstrated eccentric to concentric deficits of
greater than 15 percent.
One reason for the difference is that
Ø Eccentric testing involves a greater variability than
concentric testing.
Shape of the Curve
There is some evidence that the shape of the torque curve might be related
to patient function.
Engle and Faust tested patients with a history of shoulder subluxation.
The testing involved performing traditional and diagonal patterns of shoulder
motion.
The researchers identified consistent torque defects in symptomatic and
asymptomatic patients.
Torque curve abnormalities were found from 70 to 110 degrees with
flexion/abduction/external rotation diagonal in patients with rotator cuff
weakness.
The abnormalities were seen at 85 degrees in the
extension/adduction/internal rotation diagonal in patients with posterior
labral tearing.
Dvir et al. tested patients with patellofemoral pain.
The researchers identified a large percentage of patients
who exhibited a break in the torque curve that lasted for
10 degrees at approximately 45 degrees of flexion.
The break was associated with a load reduction of
approximately 25 percent of the patient's weight.
Pain inhibition was hypothesized to be the cause of the
break in the curve.
Testing should include multiple repetitions to identify
consistent torque curve deficits.
Figure shows a torque curve abnormality.
These graphs involve an isokinetic evaluation of a
patient who had history of significant patellofemoral pain
after an ACL reconstruction.
The lower two graphs are of the involved side.
Evaluation of the concentric force curve reveals
consistent deficits between 25 and 60 degrees.
The eccentric force curve is very inconsistent with a
decrease in force production from 35 to 60 degrees.
Pain inhibition was thought to be the contributing factor
to these force curve abnormalities.
ISOKINETIC TRAINING
Force-Velocity Curve
The use of isokinetic dynamometers should not be
limited solely to evaluation purposes.
The force-velocity curve identifies
Ø Two of the major components that athletic trainers can control in
a rehabilitation program:
force and speed.
Numerous research studies have been performed that
identify the force production with concentric and
eccentric activity with changes in velocity of motion.
Velocity increases from left to
right with concentric motion.
And velocity increases from
right to left with eccentric
motion.
Force production decreases
with increases in velocity with
concentric motion.
Conversely, eccentric force
production might increase with
an increase in the velocity of
motion.
However, some researchers disagree and feel eccentric torque
remains the same with increases in velocity.
It is important to remember that research relating to specificity of
training for speed and mode of exercise is extremely variable.
The athletic trainer should use the force-velocity curve as the basis
for designing a rehabilitation program.
The velocity and the mode of exercise should be chosen with regard
to the type of injury and the potential for force production with the
different velocities and modes of exercise.
In the acute phase of healing after injury, force production should be
kept to a minimum to allow appropriate healing of the injured
structures.
Eccentric isokinetic training is not advised in this phase because of
the potential for increased force production.
SAMPLE PROGRESSION
Progression through the rehabilitation program should be based on the
attainment of short-term goals and the phase of healing after injury.
In the acute phase of injury, the goals should be related to regaining motion
and maintenance of strength.
The isokinetic dynamometer can be used in this phase to provide isometric
and submaximal isotonic resistance and passive motion if needed.
As healing progresses and the injury enters the scar proliferation stage (7 to
21 days), graded resistive stresses can be applied to initiate the
strengthening phase of rehabilitation.
The isokinetic dynamometer can be used for submaximal to maximal
isotonics and the initiation of submaximal concentric/eccentric isokinetics.
As the injury progresses into the scar remodeling phase (21 days),
more aggressive strengthening can be added to the rehabilitation
program.
The isokinetic dynamometer can be used to alter velocity and force
production using traditional and diagonal planes of motion for
maximal isotonic and isokinetic resistance.
Isokinetic training usually follows a protocol similar to testing,
including warm-up, training sessions, and rest sessions.
The duration of the training set should be approximately 30 seconds,
followed by a rest period of 60 seconds.
The appropriate training frequency to maintain strength gains is one
time per week.
Hageman and Sorenson describe an eccentric training
progression.
The authors suggest a good warm-up followed by an
orientation to the eccentric isokinetic mode.
Training should include one to three sets of ten
repetitions beginning at 60 degrees/second in the
concentric-eccentric mode.
The clinician should advance by 30 degrees/second
increments up to 180 degrees/second,
Continuing with two to three sets of ten repetitions with
each advancing speed.
The disadvantage of isokinetics, as was previously mentioned, is
that
Ø Motion is performed in an open isokinetic chain, which is not
representative of functional activity.
However, some dynamometers can be adjusted to provide closedkinetic-chain resistance in the form of leg-press motions and
standing terminal knee extension or
Some units have a closed kinetic attachment for use with their
dynamometer.
The addition of closed kinetic activities makes the dynamometers
more versatile in the rehabilitation setting.
However, while isokinetic evaluation and training is a valuable tool
for the athletic trainer,
Ø Isokinetic testing might not be representative of functional ability in
sport-specific activity.
The athletic trainer needs to evaluate functional ability in the
functional setting and use isokinetics as a guide for progression
through the rehabilitation program.
Thanks for your attention