Isometric contraction

An isometric contraction or isometric muscle contraction occurs when a muscle only changes tension, but no change in length ( isometric , from Greek "same dimension, same length", contraction , here: "tension").

For example, the masticatory muscles do not do any work in the physical sense when clenching your teeth, but nevertheless tire quickly. Isometric contraction is also holding a weight, such as trying to lift a piano. The muscle in question does not shorten, it just changes its tension.

Isometric exercises are used in strength training to expand the range of exercises; they can also be carried out well without special equipment, even without weights.

When it comes to isometry, a fundamental distinction must be made between isometric contraction and isometric training. An isometric contraction is already present when a muscle contraction occurs without movement. In order to achieve a training effect through such a contraction, it is necessary to achieve the maximum isometric contraction force. This in turn requires a contraction time of at least seven seconds.

Exercises that are only aimed at static muscle contraction without maximum effort can, for example, help regain or improve muscular control as part of convalescence after injuries, but do not lead to an improvement in isometric maximum strength.

The maximum isometric contraction can be recognized by a violent tremor of the muscles involved in the contraction. This can be checked very clearly in a self-experiment. To do this, bend the right arm in the elbow joint to 90 ° and turn the right hand with the inner surface towards the right shoulder. Now you put your left hand into your right palms against each other. Now try to pull your right hand towards your right shoulder with maximum force, trying to prevent this with your left hand with maximum force. Immediately a strong tremor should be felt in both arms, with the biceps in the right arm and the triceps in the left arm.

Now repeat the same exercise by trying to tense with your right hand in the same arm position as possible against a suitable, rigid resistance (for example the lower edge of a non-moveable backrest of a chair on which you sit astride with your whole body weight) . It is found that the contraction force achieved is lower, so the muscular tremors are less pronounced. The lower intensity of the contraction can be impressively illustrated by EMG. A possible explanation for this could be that the sensory perception provides the nervous system with the information that further exertion is pointless, as this would anyway not lead to any movement of the chair back to be overcome. In contrast, a minor modification of the same exercise can again achieve maximum isometric contraction. To do this, you simply place a firm, elastic cushioning material between your right hand and the back of the chair and repeat the same exercise. If the cushioning material is so firm that it can be deformed but not compressed to its elastic limit, you will again feel a force comparable to the contraction against the left hand and a correspondingly pronounced tremor of the muscles.