Isotonic and Isometric Muscle Contractions

Skeletal muscle contractions are classified as isotonic or isometric, depending on the changes in the muscle length.

Isotonic contractions generate the required tension and maintain it to perform work by altering the muscle length. They have two subtypes: concentric and eccentric contractions.

For example, while lifting a weight, the bicep brachii muscle experiences an increase in tension and shortens in length to undergo a concentric contraction.

Conversely, while lowering the weight, the shortened bicep experiences decreased tension and controlled lengthening to exhibit an eccentric contraction.

Unlike isotonic contractions, the muscle length does not change in isometric contractions.

For instance, in an outstretched arm, the bicep muscle retains its resting length and still produces enough tension to maintain the stationary posture.

Besides sustaining postures, the isometric contractions stabilize certain joints during movements. For example, when the arm is moved from the front to the side of the body, the isometrically contracted bicep muscle stabilizes the elbow joint, while the shoulder joint enables the arm to move outwards.