In a laboratory study, experimental pain was induced to m vastus medialis in healthy individuals. this led to temporary reduced motor control of the knee and instability during gait (45). Other studies on patients with anterior knee pain have showed impaired coordination of motor units in m vastus medialis and m vastus lateralis (46-47). Laboratory studies have also been conducted on patients with long-term back pain. When these patients perform rapid movements of the trunk or an extremity, the activation of local muscles in the low back was delayed compared to healthy individuals (48-51). Similar muscle discoordination was seen in a study with experimentally induced pain (52).