Types of muscle work By: Dr. M. Abbas Jamil

There are three basic types of muscle contraction: isometric, isotonic, and isokinetic. An isometric or static contraction occurs when a muscle contracts, producing force without changing the length of muscle. The term isometric originates from the Greek meaning “same length.”

Isometric exercises lead to increase in the Strength of the muscles. Isometric exercises are recommended for: Power Games like sprinting, weight-lifting, boxing, shot-put etc.

An isotonic or Phasic contraction occurs when a muscle contracts, the muscle length changes, and the joint angle changes. The term isotonic originates from the Greek meaning “same tone or tension.”

Isotonic exercises lead to increase in the Endurance of muscles. Isotonic exercises are recommended for: Endurance games like Marathon running, swimming, cycling etc.

An isotonic contraction can be subdivided into : Concentric contractions eccentric contractions A concentric contraction occurs when there is joint movement, the muscles shorten, and the muscle attachments (O and I) move toward each other.

It is sometimes referred to as a shortening contraction. Picking up the weight is an example of a concentric contraction of the biceps muscle.

An eccentric contraction occurs when there is joint motion but the muscle appears to lengthen, that is the muscle attachments separate. Eccentric contractions are sometimes referred to as lengthening contractions.

After bringing the weight up to shoulder level, realize that if you relaxed your biceps muscle, the pull of gravity on your hand, forearm, and the weight would cause them to drop to the table. If you used your triceps muscle to extend the elbow (concentrically), your hand and weight would fall onto the tabletop with great force and speed. However, what you did by slowly returning the weight to the tabletop was to slow down the pull of gravity. You did this by eccentrically contracting the biceps (elbow flexor).

Quadriceps “setting” exercises are isometric contractions of the quadriceps. muscle. Flexing and extending the knee are isotonic contractions. Sitting on a chair and extending the knee is a concentric contraction of the quadriceps muscle whereas flexing the knee and returning it to the starting position would be an eccentric contraction of the quadriceps muscle.

Concentric Contractions 1. Muscle attachments move closer together. 2. Movement is usually occurring against gravity (a “raising” motion). 3. It is an acceleration activity.

Eccentric Contractions 1. Muscle attachments move farther apart. 2. Movement usually occurs with gravity (a “lowering” motion). 3. The contraction is used with a deceleration activity.

Isokinetic contraction: It can be done only with special equipment. With an isokinetic contraction, resistance to the part varies, but the velocity, or speed, stays the same.

Consider the example of the person with the 5- pound weight attached to the leg. While the person straightens and flexes the knee (isotonic contraction), the amount of resistance stays the same. That 5- pound weight remained 5 pounds throughout the range. Because of other factors, such as angle of pull, it is easier to move the leg in the middle and at the end of the range than at the beginning.

In an isokinetic contraction, the speed is preset and will stay the same no matter how hard a person pushes. However, the resistance will vary. If the person pushes harder, the machine will give more resistance, and if the person does not push as hard, there will be less resistance.