I know the co-contraction means simultaneous contraction of agonist and antagonist muscles around a joint to hold a position. I don't know what differences are there between muscle co-contraction and muscle co-activation?
Co-contraction is activity of agonist and antagonist muscle around the targeted joint. For this purpose it should estimate all forces of muscles that act around the specific joint. Eke this method is difficult in practice and the result is often have many limitation and assumptions. Muscle co-activation has been examined by comparing the EMGs of the involved muscles expressed as percentages of reference EMG values (MVC). In other word, muscle co activation is an index for demonstrating the actual co-contraction with mathematical approaches that is performed on the EMG data of agonist and antagonists which demonstrate the existence and percentage of co-contraction at any given joint and phase With this assumption that the force and the EMG activity is Correlated with each other. Beside in the literature and articles it is pronounced as Co-activation index or briefly CI.
Wish that, it helps you.
Yours truly
Alighanbari.
Farzane, I actually have a slightly different view. I have always viewed antagonist co-activation as an involuntary phenomenon. The intent is the voluntary movement or contraction of the agonist, and the antagonist gets co-activated involuntarily to provide support to the joint. However, most studies that I've read that use the term co-contraction have the subjects intentionally contract both opposing muscles. Therefore, there is no involuntary component. In addition, since both muscles (or muscle groups) are voluntarily contracted, there is no true "agonist" or "antagonist" role assigned for the contraction.
Also, antagonist co-activation would have both central and peripheral origins (peripheral origin is by the stimulation of agonist golgi tendon organs and/or antagonist muscle spindles). However, co-contraction would likely be more centrally driven.
However, it is important to note that in some of the classic, seminal literature regarding agonist-antagonist interactions, the two terms were used interchangeably. It wasn't until the 1970's to 1990's (Nielsen and Kagamihara comes to mind) that the two terms started truly possessing different meanings.
Mr. Jason M DeFreitas
I am different opinion on this issue, so I utilize an example to make this clear. Consider a high jumper athlete, this athlete want to jump in its maximum potential to reach the highest possible altitude. In this condition the athlete use his or her quad muscle group for extending the knee in the fastest and most powerful fashion that can accelerate the body in the vertical direction to jump higher. According to the article in this situation the knee flexors were active and have lower activation level compare to the knee extensors. Tis cause the energy loss or in other word some of the forces that extensor muscles were created, were neutralized by the activation of the flexors muscles. In this condition the activation of the flexors is not favorable and tis causing reduction in performance. This co-activation pattern is protecting the segment (in this example the knee articulation) and not for improving the performance. So the athlete want to reduce this co-activation pattern that it was seen in the elite athlete comparing the amateur one in literature (elite athlete have less co-activation level compare to amateur one).
Eke the activation in the flexor muscles is involuntary and automatic function of the body for protection of the joint from any form of injury. This type of activation that diminishes the performance and increase the protection pattern for segment is antagonistic eccentric activation which is cause by the reflexes of the muscle, tendon or joint instructions to tension or compression loads form internal or external sources to reduce the risk of vulnerability to injury.
Yours truly
Alighanbari
Dear Mohsen Alighanbari,
Honestly, I don't believe your last post disagreed with my statement. In your high jump example, antagonist co-activation was still described as being an involuntary process, with only the knee extensor contraction being intended. The only potential difference is that I believe that it is only partially reflex modulated. There is a significant amount of research in the last 15 years demonstrating strong supraspinal origins for co-activation.
More importantly, the question at hand was... how does co-activation differ from co-contraction? Unlike co-activation, I don't believe co-contraction has an involuntary component. Instead, the person is intentionally contracting both opposing muscles.
Warm regards,
Dr. Jason DeFreitas
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