Background and aim: Knee joint has a major role in various lower extremity activities. Among different elements of knee joint complex more interest was seen to anterior cruciate ligament because of its alignment, structural complications, more nerve receptors and susceptibility to injury. After injury of this ligament, knee extensor torque decreases but it is believed that this decrease compensated for by muscles of hip and ankle joints. This suggestion has not investigated by isokinetic studies. Therefore, the aim of this research was that if quadriceps muscle torque decreases in spite of rehabilitation process and if this decrease compensated for by hip extensors and ankle plantar flexors?

Materials and methods: 10 healthy men (age: 22-35 years old) and 10 patients with ACL deficiency (age: 23-42 years old) participated in this study. Plantar flexor muscle strength, quadriceps muscle strength and hip extensor muscle strength were tested by Isokinetic Biodex System 3 at 60 and 180 degrees of angular velocities. Also functional vertical jump test was done for each lower extremity.
Results: Will coxson test and Spearman correlation coefficient were used. Results showed that there was no significant difference between mean strength of gastrosoleus, hip extensors and sum of mean strength of gastrosoleus, quadriceps and hip extensors of patient's injured and sound limbs (P>0.05). Results showed that there was significant difference between mean strength of quadriceps of injured and sound limbs (P> 0.01). There was no relationship between gastrosoleus, quadriceps and hip extensor summation and vertical jump functional test in the patients and normal subjects (P>0.05).
Conclusion: The results show that compensation occurs in the ankle plantar flexors and hip extensors of injured lower extremity. Thus in spite of significant decrease in quadriceps strength in the injured limb, sum of mean strength of gastrosoleus, quadriceps and hip extensor muscles between injured and sound limbs was not statistically significant. Also there was no relationship between functional test and isokinetic parameters. Thus functional vertical jump test can not be used instead of isokinetic test.

Background and Aim: Several studies have investigated the effects of angular velocity on mechanical and physiological variables such as joint net torque, muscle force and myoelectrical activity, but so far its effects on the control of the pattern of synergist muscle activation during isokinetic movements have not been studied. In this experiment, a computational method of identifying and analyzing muscle synergies were used which is based on the framework of the uncontrolled manifold hypothesis to determine the variability of muscle synergies following movement velocity alteration.

Materials and Methods: Twelve healthy females without any known neurological or motor disorders participated in the experiment. The participants were positioned on a Biodex dynamometer. They were asked to perform ten continuous knee extension and flexion motions with maximal strength at 45˚/s or 300˚/s. Electromyographic activity of the vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) were recorded and variance within the UCM (VUCM) and orthogonal to the UCM (VORT) with respect to an appropriate Jacobian matrix was computed. An independent t-test was used to compare VUCM between two velocities.

Results: Across subjects, VUCM was significantly higher than VORT (VUCM>VORT) in both tasks. There was no significant difference in VUCM between two velocities (p>0.05).

Conclusion: Our findings suggest that angular velocity is not an important parameter when a controller of a multi-element system wants to stabilize a particular value of a performance variable.

Keywords: Variability, Angular velocity, Muscle synergie, Externsor muscle.