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Study Design: Factorial quasi-experimental design. Objectives: To quantify the effect of different levels of isokinetic concentric and eccentric knee extensor torques on the anterior tibial translation in subjects with anterior cruciate ligament (ACL) deficiency. Electromyogram (EMG) activity of 4 leg muscles was recorded in order to detect any co-activation of extensors and flexors. Background: The rehabilitation after an ACL injury is of importance for the functional outcome of the patient. In order to construct a rehabilitation program after that injury, it is important to understand the in vivo relationships between muscle force and tibial translation. Methods and Measures: Twelve patients with unilateral ACL injury and 11 uninjured volunteers performed 36 repetitions of a quadriceps contraction at different isokinetic concentric and eccentric torque levels, on a KinCom machine (60"-s-I), with simultaneous recordings of tibial translation (CA-4000) and EMG activity from quadriceps and hamstrings muscles. Tibial translations and EMG levels were normalized to the maximum of each subject. Results: The individual anterior tibial translation increased with increased quadriceps torque in a similar manner in both quadriceps contraction modes in all legs tested. During concentric mode, translation was similar in all groups, but during eccentric mode, the mean translation was 38% larger in the ACL injured knees. No quadriceps-hamstrings co-activation occurred in any test or group. Conclusions: An ACL deficient knee can limit the translation within a normal space during concentric muscle activity but not during eccentric activity. That limitation depends on other mechanisms than hamstrings co-activation. ] T he long-term prognosis for sports participation after an anterio r cruciate ligament (ACL) injury is uncertain, both after nonsurgical treatment and after reconstruction of the ruptured ligament.11.27 The rehabilitation after an ACL injury is of importance for the functional outcome of the patient. Various exercises included in a rehabilitation program may produce potentially harmful forces for the knee joint and stretch out the secondary restraints or the reconstructed ligament. Exercises that operate without joint compression produce large anterior shear force~~.~~.~~ and ACL strain14 compared to weight-bearing exercises that have been strongly recommended as the best form of exercise after an ACL injUry.6.14.nv25.28.39 Nanweight-bearing activities using isokinetic dynamometers, such as KinCom or Cybex, are used to quantitatively evaluate the progress of muscle rehabilitation and training.15 The recommendation to avoid non-weight-bearing exercises during the early rehabilita- tion period is not founded on sound data.I0 Specifically, Beynnon et a14 have shown that the ACL strain is almost the same in weight and non-weight-bearing exercises in normal knees. The effect of different exercises on the ACL or the secondary restraints in case of ACL deficiency, can be measured as the degree of anterior translation o...

There is a shortage of studies concerning the reproducibility of surface electromyography (EMG) during dynamic contractions. The movement per se introduces factors that could have the potential to affect the characteristics of the electromyogram. The aim of this study was to investigate the during-the-day reproducibility (using intra-class coefficient, ICC) of the peak torque (PT) and the EMG variables (without removing electrodes) of dynamic shoulder forward flexions. Eleven healthy women performed three sets of 10 dynamic maximum right-shoulder flexions at 1 h intervals using an isokinetic dynamometer. The PT of each flexion was determined. EMG signals were recorded from four muscles (trapezius, deltoid, infraspinatus and biceps brachii) using surface electrodes, and the mean frequency of the power spectrum (MNF [Hz]) and the signal amplitude (RMS [microV]), were computed. The ability to relax between maximum flexions was calculated as a ratio between the RMS during the passive extension phase and the RMS during the active flexion phase of each contraction cycle. This ratio is the signal amplitude ratio (SAR). The present study showed good reproducibility for PT, MNF and RMS, while the reproducibility of SAR was generally acceptable (fair) according to the criteria used.