Isokinetic Technology¢w
Applications in Sports Medicine and Sports Science

Ever since it was introduced in the late 1960s, isokinetic technology has made significant contribution to the assessment of rehabilitation and athletic performance by enabling more accurate and consistent quantification of the functional results of various treatment methods and training programmes. This is done through the use of specific machines which can provide an accommodating resistance to muscle activities throughout a range of motion. The data collected in the process can be used to compare the effects of different modes of treatment for sports injuries, or to correlate modes of exercise and training with the performance of athletes. Its major advantages are effectiveness, reliability, objectivity, and non-invasiveness.

From 1992 to 1995, Prof. Chan Kai-ming and his research team in the Department of Orthopaedics and Traumatology conducted a series of studies on the use of isokinetics in the assessment of muscle performance of different anatomical regions such as the knee, shoulder, ankle, and back, to define statistically the span of normality among the Chinese population, and to characterize muscle performance in sports injuries. The studies have laid a firm scientific foundation for rehabilitative regimes utilizing various models of the Cybex machine.

Knee Flexion and Extension: a Reliability Study Using the Cybex 6000 Dynamometer


Cybex 6000

This study sets out to test the reliability of the Cybex 6000 isokinetic dynamometer, a machine that is regarded as showing high reliability in measuring isokinetic variables of concentric and eccentric movements?movements in which muscle length shortens and lengthens respectively while contracting. Tests for the same isokinetic variables were repeatedly administered on the same muscle groups. The more consistent or reproducible the results, the more reliable is the Cybex 6000 isokinetic dynamometer.

The subjects were 18 males with a median age of 27 and 12 females with a median age of 26. The flexor and extensor muscle groups of both knees of the subjects were tested repeatedly for three measurements of muscle performance?peak torque, the maximal force that acts to produce a rotational movement; total work, the sum of work (force x distance); and average power, work over time. The subjects were positioned sitting at the machine and were requested to move their legs forwards or backwards using maximal effort against the accommodating resistance at a preset speed and for a preset number of test repetitions.

Testing of kness flexion/extension

The results showed that the current test is statistically reliable in obtaining all the measured parameters, among which measurement on the knee extensor muscle had better repeatability than that of the knee flexor, and the concentric mode of testing was more reproducible.

Isokinetic Strength of the Quadriceps and Hamstrings and Functional Ability of Injured Knees in Recreational Athletes

Hamstrings and quadriceps are the sets of muscles located respectively at the back and in the front of our thighs. The study tests the hypothesis that increasing the hamstrings and quadriceps isokinetic strength ratio (H:Q) through strengthening the hamstrings improves the functional ability of an anterior-cruciate ligament (ACL) deficient knee in the short term. Rupture of the anterior-cruciate ligament can result from a direct blow to the knee joint which stretches the ligament beyond its physiological stiffness, or the distal application of bending and twisting force to the limbs, or during a sudden change in direction or deceleration.

A knee being tested

Forty-six recreational athletes with completely torn ligaments were recruited for the study. The muscle performance of the subjects was measured in terms of peak torque, endurance ratio, total work, and explosive power. The functional ability of the injured knee was scored using the Cincinnati Rating System which grades items such as the severity of pain and swelling, the degree of giving way, i.e., a sudden loss of stability, and the overall ability to walk, run, ascend and descend steps, jump, and twist.

The results showed that all variables involving hamstring strength were significantly correlated to the functional ability score, whereas none of the variables involving quadricep strength showed significant correlation with the functional ability of the injured knee. The conclusion is that H:Q ratio can be used as an additional measure in the decision-making process when managing anterior-cruciate ligament deficient knees in Chinese recreational athletes.

Bilateral Isokinetic Variables of the Shoulder


The ankle dorsiflexion/plantarflexion test

Clinicians frequently want to know the pre-injury strength of an injured limb. Can it be predicted using the strength of an uninjured limb? This study tries to find out by examining a similar situation?using the strength of one shoulder to determine that of the other. Since in most people, one shoulder is used more often than the other, e.g., left for left-handers and so on, the dominant shoulder should have better muscle performance than the non-dominant one.

The study began by delineating the differences in muscle performance between the two shoulders of 30 male subjects during shoulder extension and flexion movements, and subsequently developed a method to determine the muscle performance of the dominant shoulder, based upon the measurements from the non-dominant shoulder. The results suggest a significant correlation between the dominant and non-dominant sides, with a significant difference, i.e. a constant difference in muscle per-formance between the two shoulders though it varies with the same rate of change. The results of the study indicate that it is inappropriate to use the uninjured shoulder to predict the pre-injured strength of the injured side without any adjustment. In this investigation, models were developed relating the expected maximal isokinetic measurement of the dominant shoulder to the non-dominant shoulder measurements.

Isokinetic Profile of Dorsiflexors and Plantar Flexors of the Ankle?a Comparative Study of Elite versus Untrained Subjects

The researchers also conducted a comparative study of the isokinetic characteristics of the ankle, specifically the plantar-flexion and dorsiflexion, in 23 trained and 25 untrained young men. The trained subjects comprised six cyclists, seven gymnasts, and 10 soccer players. Plantar flexion is the action of bending the foot so that the angle between the dorsal side of the foot and the leg is increased, while dorsiflexion results in a decreased angle. Plantar-flexors and dorsiflexors are respectively agonist and antagonist muscle couples whose actions are opposed to one other. In other words, the shortening of one requires the lengthening of the other. The isokinetic variables measured in the study included peak torque, torque acceleration energy, total work, and average power.

Among the subjects the cyclists had slightly higher strength but insignificant mean plantar flexion than the other subjects. The situation was reversed for dorsiflexion. The gymnasts had stronger dorsiflexion when compared with the cyclists. This shows that in sports involving jumping and running, increased attention should be given to strengthening the antagonist muscle groups in order to achieve greater agonist-to-antagonist muscle balance, thus preventing injury. The non-athletic subjects had substantially lower endurance capability in both flexors indicating that identifiable specialization in particular muscles can result from training or participating in specialized sports.

Future Developments

The studies and their data have been published in the British Journal of Sports Medicine and as a textbook entitled Principles and Practice of Isokinetics in Sports Medicine and Rehabilitation, which serves as an important reference for sports rehabilitation personnel around the world.

Prof. Chan believes that crucial to the future development of isokinetic technology is the confirmation of its usefulness and effectiveness in the overall patient care system, for example proving whether cost savings can be achieved with its applications. Further research should in particular be carried out in areas including the validity and specificity of different muscle actions such as eccentric actions and contraction, in relation to specific training and rehabilitation programmes; the metabolic characteristics of and adaptations to isokinetic training; the simplification and validation of sports-specific training programmes; and the design of user-friendly machines to bring isokinetics closer to the sports field, and hence, to cater for a wider market.

Prof. Chan Kai-ming obtained his MB BS degrees from the University of Hong Kong in 1975 and his M.Ch. (Orth) degree from the University of Liverpool in 1982. He is also a fellow of the Royal College of Surgeons of Edinburgh and the American College of Surgeons.
He is Chief of Service in Orthopaedics and Traumatology at the Prince of Wales Hospital, and director of the Centre for Sports Medicine and Health Promotion, a collaborative centre between CUHK and WHO. He is also current president of the Hong Kong College of Orthopaedic Surgeons.
Prof. Chan has been president or vice-president of various professional organizations in the field of sports medicine, including the Asia-Pacific Orthopaedics Society for Sports Medicine, the Asian Federation of Sports Medicine, and the International Federation of Sports Medicine.