Types of Muscle Contractions

Types of muscle contractions are included in some courses in introductory anatomy and physiology, human biology, sports science e.g. A-Level PE (UK), physiotherapy and related subjects. Students may be asked to explain the difference between isotonic and isometric muscle contractions.

To understand this topic keep in mind that:

  1. Muscle fibres (muscle cells) can only contract and so shorten.
  2. When stimulated (by the appropriate nerve impulse) a muscle - the whole muscle - contracts, i.e. the fibres within that muscle contract, to bring its attachments closer together but that does not necessarily result in the overall shortening of the length of the whole muscle.
  3. The whole muscle of which the muscle fibres are a part can develop force in several different ways, e.g. with the muscle as a whole shortening, lengthening or maintaining the same length while the muscle fibres contract.

List of types of muscle contraction

  • Isotonic (of which there are two types: concentric and eccentric)
    • Concentric muscle contraction
    • Eccentric muscle contraction
  • Isometric muscle contraction,
    and
  • Isokinetic muscle contraction.

These terms are explained in the following table:

Type of Muscle Contraction:

Description:

Isotonic Muscle Contraction:
meaning "same tension"

Isotonic muscle contractions are the common muscle contractions that enable people (and other animals) to move about generally.

There are two types of isotonic muscle contraction:

  • Concentric muscle contraction,
    and
  • Eccentric muscle contraction.

Concentric Muscle Contraction:

Muscle shortens as tension in the muscle increases, as when lifting a weight.

Explain:

Muscles shorten as muscle fibres contract.

 

For example when lifting an object by holding it in the right hand then contracting the biceps brachii muscles of the right-arm concentrically the elbow joint flexes, moving the lower-arm and so the hand and object held in it upwards.

Eccentric Muscle Contraction:

Muscle lengthens as tension in the muscle increases, as when slowly lowering a weight.

Explain:

Although the actin and myosin filaments within the muscle fibres contract (to produce the force needed) the fibres themselves also slide alongside each other resulting in the overall lengthening of the muscle.

 

Continuing the above example of an object that has been moved upwards by contraction of the right biceps brachii to flex the right elbow, the object may then be lowered in a steady controlled way by contracting the biceps brachii muscles of the right-arm eccentrically to extend the elbow joint, lowering the lower-arm together with the hand and object held in the hand.

Isometric Muscle Contraction:
meaning "same distance",
i.e. static

In isometric muscle contraction the muscle maintains the same length as tension in the muscle increases, as when holding a weight in a static position for an extended period of time.

That is, there is no change in the length of the contracting muscle during isometric muscle contraction. The amount of force a muscle can produce during an isometric contraction depends on the length of the muscle at the point of contraction. Each muscle has an optimum length at which the maximum isometric force can be produced.

Explain:

The force of the contraction occurs in the muscle fibre but the muscle fibres themselves do not move relative to each other, so the overall length of the muscle doesn't change.

 

For example when holding or gripping an object such that there is a downward force on the object (due to gravity) which the muscles oppose in order to hold the object in a static position (holding) and/or to maintain steady contact with the object e.g. with fingers wrapped around a handle (gripping). The hand/arm are not moving but the muscles are contracted in order not to release/drop the object.

 

Isokinetic Muscle Contraction:
meaning "same speed"

As in isotonic contractions (see above), in isokinetic muscle contraction the muscle changes length during the contraction. In isokinetic muscle contraction the muscle contracts maximally throughout its full range of movement.
The defining characteristic of isokinetic muscle contractions is that they result in movements of a constant speed. A piece of equipment called an Isokinetic Dynamometer is used to measure the (constant) speed of isokinetic muscle contraction. Such equipment is not common in all schools, colleges, leisure centres and gyms but tends to be used in rehabilitation centres and specialist sports training facilities.

Explain:

The changes in overall length of the whole muscle depend on the combined effects of contraction (shortening) of muscle fibres and movement of individual muscle fibres alongside each other (potentially increasing overall muscle length).

Compare isotonic muscle contraction with isometric muscle contraction

As summarized in the following table:

 

Movement
(resulting from muscle contraction)

Change in overall length of muscle

Isotonic (muscle contraction)

MOVEMENT occurs

(direction of movement depends on type of contraction, i.e. concentric or eccentric)

Length of muscle CHANGES

(concentric contraction => muscle shortens
eccentric contraction => muscle lengthens)

There are 2 types of isotonic muscle contraction:

  • Concentric
  • Eccentric

Isometric (muscle contraction)

 

 

No movement

No change in muscle length

Isotonic muscle contraction is when contraction of a muscle results in movement accompanied by a change in the length of the overall muscle involved. Conversely, isometric muscle contraction is when contraction of a muscle does not result in either movement or any change in the length of the muscle itself (e.g. due to some other force such as the weight of an object opposing the force applied by the isometric muscle contraction).

See also other pages about muscles and movements at joints.

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