imbalances (either left/right or agonist/antagonist relation- ships), because it is thought that muscle imbalance is related to injury. Hamstrings to quadriceps ratios ...
Applied Ergonomics 1991, 22.5,295-298
Ergonomics and sport
Isokinetic exercise in rehabilitation J.M.H. Cabri and J.P. Clarys Free University of Brussels,Faculty of Medicine and Pharmacy,Departmentof Experimental Anatomy, Laarbeeklaan103, B-1090 Brussels,Belgium
Since isokinetic equipment was first designed in the late 1960s, many investigations have focused on the agonist-antagonist relationships, left-right imbalances and so on, in order to present normative data for the assessment of musculoskeletal injuries. Furthermore, the isokinetic principle has been applied in rehabilitation to minimise rehabilitation time, because it is thought that it may give a close-to-optimal training stimulus to the musculoskeletal system. However, much research still needs to be carried out in this field, in order to determine which evaluation protocols are relevant, which training regimen is optimal, and which angular velocities should be used to assessand/or rehabilitate muscle strength.
Keywords: Isokinetic, exercise, rehabilitation, injury, muscle
Isokinetic exercise A valuable feature of isokinetic exercise (testing, training, therapy, assessment) is that the amount of moment produced by the athlete or patient is given in a unit of measure (foot-pounds or newton-metre). This feature makes it possible to obtain a measure of the 'functional' capability of a muscle group at a certain joint. The moment produced represents the interaction between the lever arm of the motion and the expression of the muscular moments as they act around a joint (Coplin, 1971). The trainer and therapist have now a tool with which strength can be expressed as a value. This allows them to compare muscle groups on one side of the body with their heterolateral counterparts, and to evaluate progression during a given training or therapeutic programme. The objective quantitative features of the dynamometer can also be used to provide normative data for assessment of a group of subjects/athletes/patients and can therefore be used as a reference for the individual (e g, Griffin et al, 1986; Sunnegardh et al, 1988; Backman and Oberg, 1989; Cahalan et al, 1989).
Isokinetic assessment A number of studies have dealt with the use of isokinetic exercise as a means for assessment and rehabilitation of muscle and joint function after injury or surgery (Sherman et al, 1982). Considerable interest in isokinetic dynamometry lies, for instance, in the determination of muscle imbalances (either left/right or agonist/antagonist relationships), because it is thought that muscle imbalance is related to injury. Hamstrings to quadriceps ratios (H/Q) have been studied in numerous investigations (e g, Moffroid et al, 1969; Scudder, 1980; Osternig et al, 1986; Baratta et al, 1988; Westing and Seger, 1989) because of the important
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role of both muscle groups in knee stability. A H/Q ratio of 1 would indicate equal strength in both muscle groups; however, values ranging from 0.41 to 0.87 have been reported depending on the angular velocity at which isokinetic strength was determined, the subjects selected and the physical fitness of the subjects. When correction for gravity was implemented, values ranged from 0-61 to 0.71 0Vesting and Seger, 1989). An overall trend can be observed: as limb velocity decreases, so does the H/Q ratio (Scudder, 1980; Westing and Seger, 1989). Alexander (1990) used peak torques to describe strength estimates of the major muscle groups of the lower limbs for a group of elite sprinters, both in eccentric and concentric conditions of agonists and antagonists. The peak torque values for the flexor and extensor muscle groups of the hip, knee, and ankle joints were tested. The peak torque values for the knee joint were found to be substantially larger than those reported for non-athletes, and comparable with those for other athletic populations. No comparable scores were located for the results from the hip and ankle joints. The flexion and extension ratios for the knee joint, at approximately 0.60, were similar to others reported, whereas the ratios for the hip joint were larger at 0.76. The concentric and eccentric ratios varied, depending on the speed of testing and the joint tested. Kannus and Jarvinen (1990) evaluated the peak torque and total work of the hamstring/ quadriceps (H/Q) ratios of 77 knees with a previous grade 1 distortion injury to find the possible relationship between different H/Q ratios and long-term outcome. Peak torque values were recorded at low (1434 rad/s) and high (3"14 rad/s) speeds of isokinetic movement, and the maximal isometric extension and flexion outputs were measured with the knee at a 60 ° angle. They found that the H/Q ratio is an idiosyncronatic parameter: it is patient-specific and any general recommendation about optimal value is difficult to give. The authors also concluded that analysis
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of the total work, the "peak torque acceleration energy" and average power of multiple contractions offers little additional information to that attained by more simple measurement, the peak torque analysis (Kannus, 1988; Kannus and Jarvinen, 1989).
ment of the strength of the knee extensor muscles is depicted in Fig. 1. The mean maximal strength of the injured leg was dramatically reduced, in comparison with the healthy knee. At rapid movement speeds, no strength measurements could be carried out because of pain.
It must be noted that in these studies the peak torque was used as a measure of strength, without considering biomechanical and physiological confounding factors (see below). Prietto and Caiozzo (1989) examined the in vivo force-velocity relationship using an angle-specific method and a gravitational correction factor, in order to determine more accurately flexor-extensor ratios and to describe better any variations occurring as a result of the changing angular velocities. Six angular velocities were tested: 0, 0.83, 1 "67, 2.51,3.35,4-18 rad/s. At these respective test speeds, the H/Q ratios were 37.6, 38.4, 38.1,35-8, 34.7 and 33.6 %, respectively. Normalisation of these torquevelocity relationships demonstrated that the in vivo forcevelocity relationships of the two muscle groups are similar at slow speeds, but become disparate at higher velocities. According to Solomonow et al (1987) a primary fast-to-respond reflex arc exists from the mechanoreceptors in the anterior cruciate ligament to the hamstrings group, which may allow the antagonist muscle to act as a torque generator that is activated 'on demand' during ligament overloading, resulting in an 'active' joint stabiliser. Therefore it can be assumed that, with increasing limb velocity, the contribution of the hamstring muscle group becomes more and more important to assure stability of the knee. Solomonow et al also stressed that muscle strengthening therapy, especially of the hamstrings, has a significant potential for improving knee stability in patients with anterior cruciate ligament (ACL) deficiency.
After 15 weeks of immobilisation, a progressive but intensive isokinetic rehabilitation programme was started (in conjunction with functional exercises at a later stage of the programme). After 8 weeks of rehabilitation (three times per week, during 30 to 45 minutes) which included isometric and isokinetic exercises (progressively increasing angular velocity and range of movement), the strength of
Some authors (e g, Grimby et al, 1980; Grimby, 1985) have reported the beneficial effect of isokinetic exercise after knee ligament surgery, in contrast to 'isotonic' training, but cautioned that additional training programmes including follow-up measurements are useful for longer periods than the conventional physiotherapeutic programmes. The advantage of isokinetic training and the explanation for its beneficial effect over other training modalities can be found in the fact that the device gives maximal load through the full range of motion - except at the beginning and the end of the movement where the lever arm accelerates and decelerates (Grimby, 1985). For an extensive review and some critical insights on this subject, the reader is referred to Osternig (1986), Baltzopoulos and Brodie (1989) and Rothstein et al (1987).
Status report at start
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In order to demonstrate the clinical applications of isokinetic exercise, two case studies are presented. Both involve soccer players in the later stages of their professional careers. Case study 1 : Medial resection of patellar tendon This 32-year old professional soccer player (goal keeper), suffering from a partial rupture of the pateUar tendon, and was surgically treated by the resection of the medial (necrotic) part of the injured ligamentar tissue. The assess-
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Fig. 1
Mean maximal isokinetic strength values of the knee extensors in a patient with medial patellar rupture. Negative angular velocities represent the eccentric efforts, positive angular velocities represent the concentric efforts. The upper graph is a status report atthe beginning of the isokinetic rehabilitation programme. The lower graph represents a progress report before (Uninjured and Injured 1 ), during (Injured 2) and after (Injured 3) the rehabilitation programme
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the quadticeps muscle was significantly increased, becoming significantly greater than found in the healthy leg.
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Case study 2: Tibial and fibular fracture This patient was a 33-year old male who was injured in the right tibia and fibula during a soccer game. Repositioning of the fractures was carried out by means of an external fixator. After full consolidation of the fracture, the patient was treated for general muscle weakness of both plantar and dorsal flexors of the ankle and of knee extensors and flexors due to the long (over 1 year) period of immobilisation, Rehabilitation included slow isokinetic movements at reduced ranges of movement, progressing in movement speed, intensity and amplitude of the weakened muscle groups, and was prolonged to 12 weeks, 3 times per week during 30 minutes. In this case, it was important to increase not only maximal strength but also endurance strength because of the general muscle weakness of the lower extremity muscles. Therefore, it was decided to incorporate normal walking and running proprioceptive exercises into the rehabilitation programme,
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The assessment of the isokinetic strength of the dorsal and plantar flexors is shown in Fig. 2. It was found that these muscles were extremely reduced in the strength productive capacities, and after 12 weeks of strength training, satisfactory gains could be demonstrated. However, at higher angular velocities both concentric and eccentric strength did not totally recover, although the differences found were not of any significance.
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Some of the advantages of isokinetic exercise may be safety, accommodating resistance and the facility for strength analysis. However, a number of restrictions and limitations apply when interpreting strength measurements. Isokinetic strengthening may be valuable in the initial phase of a rehabilitation programme for a close-to-optimal stress is given by the device in well controlled ranges of movements, minimising the risk of muscular and ligament strains. However, much research needs to be done in this field in order to determine which evaluation protocols are relevant to the clinician/coach, which training regimen is most beneficial for a given rehabilitation programme (or training schedule), what are the angular velocities at which one should assess muscle strength, and so on. This will enable exchange of data between laboratories, hospitals and general practitioners for comparative and normative purposes.
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Mean maximal isokinetic strength values of the dorsal (upper graph) and plantar (lower graph) ankle flexors in a post-traumatic patient. Negative angular velocities represent the eccentric efforts, positive angular velocities represent the concentric efforts. Measurements were taken before (Uninjured and Injured 1) and after (Injured 2) the rehabilitation programme
Baratta, R., Solomonow, M., Zhou, B., Letson, D., Chuinard, R., and D'Ambrosia, R. 1988, A m J Sports Med, 16, I 13-122. Muscular coactivation. The role of the antagonist musculature in maintaining knee stability.
Cahalan, T.D., Johnson, M., Liu, S., and Chao, E. 1989, Clin Orthop, 12, 136-145. Quantitative measurements of hip strength in different age groups.
References
Alexander, M.J. 1990,Arch PhysMedRehabil, 7 1 , 3 3 4 339. Peak torque values for antagonist muscle groups and concentric and eccentric contraction types for elite sprinters.
Backman, E., and Oberg, B.
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Baltzopoulos, V., and Brodie, D.A.
1989, Sports Med, 8, 101 - 116. Isokinetic dynamometry: applications and limitations.
Coplin, J. 1971,J Nat Athletic Trainers Ass, 6,222. Isokinetic exercise: clinical usage. Griffin, J.W., MeClure, M.H., and Bertorini, T.E. 1986, Phys Ther, 66, 32-35. Sequential isokinetic and manual testing in patients with neuromuscular disorders. Grimby, G. 1985, SportsMed, 2 , 3 0 9 - 3 1 5 . Progressive resistance exercise for injury rehabilitation. Special emphasis on isokinetic training. Grimby, G., Gustafsson, E., Peterson, L., and Renstrom, P. 1980, Med Sci Sport Exerc, 12, 70-71. Quadriceps function and training after knee ligament surgery.
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Ergonomics and sport Kannus, P. 1988, lnt J Sports Med, 9 , 2 9 4 - 2 9 6 . Relationship between peak torque and total work in an isokinetic contraction of the medial collateral ligament insufficient knee. Kannus, P., and Jarvinen, M. 1989, Med Sci Sports Exerc, 21,304-307. Prediction of torque acceleration energy and power of thigh muscles from peak torque. Kannus, P., and Jarvinen, M. 1990, Arch Phys Med Rehabil, 71, 38-41. Knee flexor/extensor strength ratio in follow-up of acute knee distortion injuries.
Moffroid, M., Whipple, R., Hofkosh, J., Lowman, E., and Thistle, H. 1969, J Am Phys Ther Assoc, 7. A study of isokinetic exercise. Osternig, L.R. 1986, Exerc Sport Sci Rev, 14, 4 5 - 8 0 . Isokinetic dynamometry: implications for muscle testing and rehabilitation. Osternig, L.R., Hamill, J., Lander, J., and Robertson, R. 1986, Med SciSportsExerc, 4, 431-435. Co-activation of sprinter and distance runner muscles in isokinetic exercise. Prietto, C.A., and Caiozzo, V.J. 1989, A m J Sports Med, 17,607-611. The in vivo force-velocity relationship of the knee flexors and extensors.
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Rothstein, J.M., Lamb, R.L., and Mayhew, T.P. 1987, Phys Ther, 67, 1840-1844. Clinical uses of isokinetic measurements. Critical issues. Scudder, G.L. 1980, A r c h P h y s M e d & R e h a b , 61,68-72. Torque curves at the knee during isometric and isokinetic exercise. Sherman, W.M., Pearson, D.R., Plyley, M.J., Costill, D.L., Habansky, A.J., and Vogelsang, D.A. 1982, A m J Sports Med, 10, 155-161. Isokinetic rehabilitation after surgery: a review of factors which are important for developing physiotherapeutic techniques after knee surgery. Solomonow, M., Baratta, R., Zhou, B., Shoji, H., Bose, W., Beck, C., and D'Ambrosia, R. 1987, Am J Sports Med, 15,207-213. The synergistic action of the anterior cruciate ligament and thigh muscles in maintaining joint stability.
Sunnegardh, J., Bratteby, L., Nordesjo, L., and Nordgren, B. 1988, Eur J Appl Physiol, 58, 291-297. Isometric and isokinetic muscle strength, anthropometry and physical activity in 8- and 13-year old Swedish children. Westing, S.H., and Seger, J. 1989, l n t J Sports Med, 10, 175-180. Eccentric and concentric torque-velocity characteristics, torque output comparisons, and gravity effect torque corrections for the quadriceps and hamstring muscles in females.
