Kinetic chain weight training, strength assessment, and functional performance testing: with reference to sports and rehabilitation

Abstract: The overall purpose of the studies was to obtain knowledge about physical performance in healthy individuals and patients after anterior cruciate ligament (ACL) reconstruction. Data are presented that concerns closed and open kinetic chain exercise, adaptive response to weight training, the methodology of muscle strength assessment, and the development of a functional testing protocol performed under conditions of fatigue.Study I: The purpose of this study was to compare the effect of closed versus open kinetic chain weight training of the thigh muscles. Healthy subjects performed closed (n=12) and open (n=12) kinetic chain weight training twice a week for six weeks. Both groups increased in a barbell squat test, although the closed kinetic chain group improved more than the open kinetic chain group. The closed kinetic chain group improved their jumping ability, however, there was no difference across groups. Large improvements in isotonic strength in both groups did not transfer to an isokinetic knee-extension test.Study II: The purpose of this study was to investigate the ability of closed and open kinetic chain strength tests to assess functional performance in 16 healthy male subjects. Moderately strong correlations were found between a barbell squat test, an isokinetic knee-extension test, and a vertical jump test. It is suggested that the effect of training or rehabilitation interventions should not be based exclusively on tests of muscular strength. Instead, various forms of dynamometry including functional performance tests could be recommended.Study III: The purpose of this study was to investigate the effect of "pre-exhaustion" exercise (knee-extension) on lower-extremity muscle activation during a leg press exercise. Seventeen healthy male subjects performed one set of a leg press exercise with and without pre-exhaustion. The electromyography activation of the vastus lateralis and the rectus femoris muscles was less when pre-exhausted. Our findings do not support the popular belief that performing pre-exhaustion exercise more effectively enhances muscle activity compared with regular weight training.Study IV: A pre-exhaustion exercise protocol was combined with single-leg hop testing to improve the possibilities to evaluate the effects of training or rehabilitation interventions. High test-retest reliability was noted for 11 healthy male subjects performing non-fatigued and fatigued hop testing. Additionally, we investigated how fatigue influences lower-extremity joint kinematics and kinetics during single-leg hops. Absorbed power during landing was two to three times greater for the knee than for the hip and five to ten times greater for the knee than for the ankle across test conditions.Study V: A new hop test, performed under conditions of fatigue, was investigated to determine functional deficits after ACL reconstruction. Although no patients (n=19) displayed abnormal hop symmetry when non-fatigued, two thirds showed abnormal hop symmetry for the fatigued hop condition. It is concluded that a fatigue exercise protocol combined with the single-leg hop test improved testing sensitivity when evaluating lower-extremity function after ACL reconstruction.Conclusions: Although strength measurements are important to monitor the effect of training and rehabilitation interventions, they cannot fully assess functional performance. Functional deficits after ACL reconstruction may become more apparent during conditions of fatigue. For a more comprehensive evaluation of lower-extremity function after ACL reconstruction, it is therefore suggested that functional testing should be performed under both non-fatigued and fatigued test conditions.