Objective: The purpose of this study is to evaluate concentric and eccentric trunk muscle strength in patients with chronic low back pain and compare it with healthy controls to determine the role of trunk muscle in chronic low back pain

Method: Subjects were 20 chronic low back pain patients with the duration at least 6 months and 20 normal adults. Concentric and eccentric isokinetic trunk muscle test was performed at specific speeds (30^o, 60^o, 120^o/sec) with Cybex 770 machine in back pain patients and healthy control.

Results: The strength of trunk flexor and extensor muscles of chronic low back pain patients was significantly weaker than that of normal controls. Eccentric peak torque was significantly higher than concentric peak torque in both patients and healthy control. A concentric and eccentric ratio of patients was lower than that of normal controls. The correlation between concentric and eccentric variables was high. Our results show that concentric peak torque has the highest correlation with eccentric peak torque.

Conclusion: Isokinetic evaluations of the trunk muscle offer objective and quantitative data of patients with chronic low back pain and will be clinically useful in muscle power measurement of lumbar muscles.

The understandings of the characteristics of eccentric exercise are very important because all sports and daily activities under the gravity force should be well coupled between concentric contraction and eccentric contraction as accelerator and decelerator respectively. We tested 40 knee flexors and extensors of 20 normal young persons at different anglular velocities of 60^o/sec and 120^o/sec using Cybex 6000(A division of Lumax, New York) isokinetic dynamometer in order to know the characteristics of eccentric isokinetic contraction parameters by comparing with concentric isokinetic parameters.

Compared to the concentric isokinetic contraction, eccentric isokinetic the peak torque and average power values of knee extensor and flexor muscles showed negative values which means that eccentric contractions were coupled with concentric contractions as decelerator and energy absorptioner. The peak torque values of eccentric contraction were 38∼61%, 44∼79% higher in flexor and extensor, respectively than those of concentric contraction and not so decreased as the peak torque of concentric contraction decreased in high angular velocity. The average power values of knee flexor and extensor muscles were definitely low in eccentric contracton than those of concentric contraction but were increased simultaneously with high angular velocity contraction. Further studies about the velocity dependency, muscle soreness, methodology to measure real eccentric activities and other parameters of eccentric contraction are needed imminently.

Isotonic exercise occurs when the tension or torque generated by a muscle is constant throughout the movement. In practice it is very difficult to maintain the tension constant. Evaluation of isotonic exercise should include the works of concentric and eccentric contraction and the changes in tension and torque during joint motion. However, optimal evaluation tools for isotonic exercise has yet to be developed.

We authors, used virtual reality motion analysis system(VRMAS) which was codeveloped by us and EMG system(Cardwell Excel). Healthy male adult subjects(n=10) were recruited from hospital personnel. After dominant upper arm and trunk of each subject was fixed with velcro, he was instructed to repeat flexion and extension of his dominant elbow grasping dumbell (9 kg) in hand with maximal velocity as possible as can until the point of exhaustion. We measured the elbow angle, the angular velocity, torque, power, total work and the work of concentric and eccentric contraction during exercise.

The results were as follows: there were four distinct elbow flexor muscle contractions during flexion and extension of the elbow with the first and the second contractions during concentric contraction and the third and the fourth contractions during eccentric contraction. Between the peaks of contraction, motion was maintained due to the momentum that was generated. Of the ten subjects, seven had higher concentric work than eccentric work with the eccentric work being higher in the remaining three. But there was no statistic significance between the works of concentric contraction and eccentric contraction(p>0.05). The biggest work was observed in the fourth contraction, while the third contraction showed the least work(p<0.05).

In conclusion, there were four distinct muscle contractions during elbow isotonic exercise and the works of each muscle contraction were different. This result is contrary to the definition of isotonic exercise. This study also shows that the VRMAS could be a very useful evaluation tool for several types of isotonic exercise.