Isokinetics
SUMMARY
- The isokinetic dynamometer affords a computerised, reliable, reproducible method of evaluation of muscle torque, power and work in both concentric and eccentric modes for muscles around peripheral joints
- Isokinetics is the only method to maximally resist a muscle at its strongest point in the range of motion
- Rehabilitation can therefore be 'fast tracked' as the client can be encouraged to work at maximum effort though range and therefore deficits of more than 30% can be overcome in 6 sessions
- Isokinetics is an adjunct to functional rehabilitation
- Isokinetics on the Kin Com can used in closed chain and can test both torque and endurance
- Isokinetic testing allows the clinician to accurately decide when a client is fit to return to sport or physical activity when deficits are below 20%.
- With isokinetic testing a profile of the muscle can be demonstrated, and compared with normative values. This includes
o Left/right comparisons
o Angle of peak torque
o Average torque
o Eccentric/concentric ratios
o Antagonist/agonist ratios
o Fatigue , work and power deficits
o Torque to body weight ratios
What is Isokinetics?
o Isokinetics = fixed speed variable resistance and range of motion
o Isotonics = fixed resistance variable speed and range of motion
o Isometrics = fixed range of motion variable speed and resistance
History of the isokinetic dynamometer
Isokinetic exercise and testing has been available since 1970. It was originally a tool used mainly in exercise science and the only in concentric mode with no continuous passive motion (CPM) or eccentric mode. Around 1984 the world of isokinetics changed dramatically. Servo motors and microprocessors transformed the early machines into fast and dynamic tools offering instant data analysis and reproducibility. Testing became as important as exercise.
What can be tested?
The shoulder, hip, knee, ankle, elbow and wrist can be tested on the KIN-COM isokinetic dynamometer. The limb to be tested is attached to the dynamometer via a padded cuff, which is attached to a housing containing strain gauges. The dynamometer head and the chair can be moved along a metal lever arm to accommodate different limb lengths.
Regulating speed
The machine is designed to 'ramp up' the resistance if the subject attempts move faster than the preset speed, producing a force equal in magnitude but opposite in direction, thereby resulting in a constant angular velocity of the limb. This has been termed "accommodating resistance."
The KIN-COM isokinetic dynamometer
Measurements
The Kin-Com measures the force, angle, and velocity signals through load cells in the lever arm. Angle measurements are obtained by a potentiometer, and velocity measurements are obtained by a tachometer.
Reliability
Mayhew et al in 1994 conducted a reliability study and found a very strong relationship between the measurements from the Kin-Com dynamometer and known weights, angles, and selected velocities under research conditions. Hanten (1988) validated reliability of torque, work and power in the Kin Com.
Muscle performance
The Kin Com tests muscle performance. Basic muscle performance is related to the length tension curve. The point at which there is maximum attachment of cross bridges is the point of maximum torque production and this is represented as a graph. Torque can be measured
in concentric mode (when the cross bridges attach) and eccentric mode (when the cross bridges are detached).
Normative values
Zeevi Dvir's book Isokinetics . Muscle Testing, Interpretation and Clinical Applications reviewed normative values in published papers in peer review journals for all peripheral joints.
There are well established normative values for:
* antagonist/agonist ratios. Both conventional ( concentric antagonist: concentric agonist) and functional ( eccentric antagonist: concentric agonist) ratios. For example in the knee this is 60% and 80% respectively at slow speed (30°/second)
* eccentric/ concentric ratios. Normal on the KIN-COM is greater than 150%
What the shape of the graphs might show
Occasionally graphs have particular shapes that appear to be related to specific problems. No clinical research has been published as yet to prove this but clinicians experienced in using isokinetics have come to recognise the significance of certain graph shapes which, when related to clinical signs, may indicate a problem that might need surgery such as a plica, or ACL insufficiency..
A dip in mid range hamstring torque between 50° -70° range of motion may relate to ACL insufficiency.
A dip in the middle of the quadriceps curve at approximately 60° range of motion may indicate patellofemoral instability, the existence of a plica or meniscal dysfunction.
How do you know when a client has fully recovered?
Case study
A 30 year old woman who played regular rugby had tibial tuberosity transfer surgery. Following a 6 month functional rehabilitation programme the client was deemed ready to return to her sport. At
this point she was running, jumping, performing weighed squats and had good balance and plyometrics.
An isokinetic test was done for the quadriceps and hamstring muscles. The graph above demonstrates deficits in quadriceps concentric and eccentric torque of 62%. After 6 sessions of rehabilitation on the KIN-COM these deficits had reduced to less than 20% and she was then able to start training. Without this test she might have gone back to sport and suffered a breakdown of the knee..
How do you know when your client is reaching their goals?
Isokinetics can:
* Establish when deficits are less than 20% and the point at which the client is ready to go back to activity or training for sport
* Evaluate left/ right peak and average torque in both concentric and eccentric modes and at any angle in the range tested
* Compare antagonist/ agonist ratios to normative values.
* Compare eccentric /concentric ratios to normative values.
* Compare original test to re-test to record improvements.
* Compare preoperative tests to post-operative tests
* Compare the angle of peak torque between muscles to see if there are length tension differences
* Identify patellofemoral maltracking, a plica or ligament instability such as ACL by the shape of the curve.
Exercise and rehabilitation programmes
Exercise programmes can be as adaptable as needed. Any speed from 0-300° per second can be chosen for rehabilitation. A slow speed of say 30° per second will replicate walking up or down steps and a moderate speed of 120° per second will replicate walking at a reasonable pace while 180° per second would be like a moderate running pace.
A series of reps and sets can be designed specifically for the client using a mixture of speeds and concentric or eccentric modes or a combination of both.
Passive mode
In early rehab stages the passive mode will allow continuous passive motion to aid reduction of swelling and prevent loss of motion.
Gradual strengthening can be introduced using minimal resistance as comfortable. With visual biofeedback from the screen it is possible to aim for certain resistance levels equal to body weight or a percentage of body weight if required according to the stage of recovery.
We would advocate using the passive mode in closed chain at low levels of resistance in the first 3 weeks following knee surgery to improve range of motion and reduce swelling.
Closed chain
With a special attachment closed chain exercise can be done which allows early rehabilitation. (Donatelli) We use the closed chain mode following ACL reconstruction for up to 6 weeks at which point we expect toque in eccentric mode to be equal to 150% body weight so that we are sure that the client can walk downstairs with good control. (Hooper)
Eccentric mode
Isokinetics is the easy way to isolate eccentric muscle rehabilitation. This allows loading of tendons to improve torque, reduce pain and aid remodelling of the tendon in tendonopathies such as epicondylopathy (Croisier) and patella tendinopathy (Dvir).
The eccentric mode is also important in improving antagonist deceleration of a joint such as the hamstring action in the knee and has been associated with reduction in muscle injury in the hamstring muscle. With rotator cuff or shoulder impingement problems frequently the posterior cuff muscles are weak and particularly in eccentric mode.
Continuous mode
Continuous testing is important to check fatigue and power particularly for anyone involved in active sport. It is possible to test antagonist and agonist muscles in concentric mode only or to test one muscle in eccentric and concentric modes thereby replicating non weight bearing plyometrics.
Injury prevention
Isokinetic testing can help to prevent injuries. Hamstring/ quadriceps imbalance has been implicated in knee problems and hamstring muscle injury. (Croisier). Testing to establish muscle balance and strength training if there is an imbalance can help to prevent injury.
References
1. Hanten, W.P., and Lang, J.C. (1988) Reliability and validity of the Kinetic Communicator for the measurements of torque, work and power. Physical Therapy, 68(5), 825 (Abstract).
2. Mayhew, T.P., Lamb, R.L., and Rothstein, J.M. (1994) Performance characteristics of the Kin-Com dynamometer. Physical Therapy, 74(11), 1047- 1054.
1. Uh B S et al. The Benefit of a Single-Leg Strength Training Program For the Muscles Around the Untrained Ankle. A Prospective, Randomized, Controlled Study. Am J Sports Med, Vol. 28, No. 4. 2000
2. Donatelli, R et al. (1996) Open and closed chain kinetic strength training versus function al exercises to improve performance in patients with ACL reconstructed knees: a prospective study, Isokinetics and Exercise Science, 6 (1), 7-13
3. Dvir, Z et al. (1991a) Quadriceps function and pattelo-femoral pain syndrome - Part 1. Isokinetics and Exercise Science, 1, 26-30
4. Dvir, Z et al. (1991b) Quadriceps function and patello-femoral pain syndrome- Part 2. Isokinetics and Exercise Science, 1, 31-35
5. Dvir, Z (1995) Isokinetics. Churchill Livingstone, Singapore
6. Farrell, M & Richards, J G (1986) Analysis of the reliability and validity of the kinetic communicator exercise device. Medicine and Science in Sports and Exercise, 18, 44-49
7. Hooper, D M et al. (2001) Open and closed kinetic chain exercises in the early period after anterior cruciate ligament reconstruction, American Journal of Sports Medicine, 29 (2), 167-174
8. Shklar, A and Divir, Z (1994) Normative values of shoulder muscles performance,
9. Croisier Jean-Louis et al. An isokinetic eccentric programme for the management of chronic lateral epicondylar tendinopathy Br J Sports Med 2007;41:269-275 2006.
10. Croisier Jean-Louis et al. Treatment of recurrent tendinitis by isokinetic eccentric exercises Isokinetics and Exercise Science 9 (2001) 133-141
11. Croisier Jean-Louis et al. Strength Imbalances and Prevention of Hamstring Injury in Professional Soccer Players. A Prospective Study. Am J Sports Med 2008 vol. 36 no. 8 1469-1475
Elizabeth Sharp MSc MCSP
Clinical Director
esph
www.esph.co.uk
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