Isotonic, Isometric, Eccentric and Concentric Muscle Contractions

Isotonic, Isometric, Eccentric and Concentric Muscle Contractions
Types of Muscle Contractions: Isotonic and Isometric
Last updatedMay 25, 2020
9.3D: Muscle Tone

9.4: Muscle Metabolism
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Muscle contractions are defined by changes in the length of the muscle during contraction.

Learning Objectives

Differentiate among the types of muscle contractions
Key Points
Isotonic contractions generate force by changing the length of the muscle and can be concentric contractions or eccentric contractions.
A concentric contraction causes muscles to shorten, thereby generating force.
Eccentric contractions cause muscles to elongate in response to a greater opposing force.
Isometric contractions generate force without changing the length of the muscle.
Key Terms
Isometric: A muscular contraction in which the length of the muscle does not change.
isotonic: A muscular contraction in which the length of the muscle changes.
eccentric: An isotonic contraction where the muscle lengthens.
concentric: An isotonic contraction where the muscle shortens.
A muscle fiber generates tension through actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same. Although the term contraction implies shortening, when referring to the muscular system, it means the generation of tension within a muscle fiber. Several types of muscle contractions occur and are defined by the changes in the length of the muscle during contraction.

Isotonic Contractions
Isotonic contractions maintain constant tension in the muscle as the muscle changes length. Isotonic muscle contractions can be either concentric or eccentric.

Concentric Contractions
A concentric contraction is a type of muscle contraction in which the muscles shorten while generating force, overcoming resistance. For example, when lifting a heavy weight, a concentric contraction of the biceps would cause the arm to bend at the elbow, lifting the weight towards the shoulder. Cross-bridge cycling occurs, shortening the sarcomere, muscle fiber, and muscle.

Eccentric Contractions
An eccentric contraction results in the elongation of a muscle while the muscle is still generating force; in effect, resistance is greater than force generated. Eccentric contractions can be both voluntary and involuntary. For example, a voluntary eccentric contraction would be the controlled lowering of the heavy weight raised during the above concentric contraction. An involuntary eccentric contraction may occur when a weight is too great for a muscle to bear and so it is slowly lowered while under tension. Cross-bridge cycling occurs even though the sarcomere, muscle fiber, and muscle are lengthening, controlling the extension of the muscle.

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Types of Muscle Contraction: An isotonic concentric contraction results in the muscle shortening, an isotonic eccentric contraction results in the muscle lengthening. During an isometric contraction the muscle is under tension but neither shortens nor lengthens.

Isometric Contractions
In contrast to isotonic contractions, isometric contractions generate force without changing the length of the muscle, common in the muscles of the hand and forearm responsible for grip. Using the above example, the muscle contraction required to grip but not move a heavy object prior to lifting would be isometric. Isometric contractions are frequently used to maintain posture.

Isometric contractions are sometimes described as yielding or overcoming.

Yielding
A yielding contraction occurs when a muscle contraction is opposed by resistance. For example, when holding a heavy weight steady, neither raising nor lowering it.

Overcoming
An overcoming contraction occurs when a muscle contraction is opposed by an immovable object, such as the contraction generated in the muscles when pushing against a wall.

In both instances, cross-bridge cycling is maintaining tension in the muscle; the sarcomere, muscle fibers, and muscle are not changing length.
Muscles
The majority of muscles in the leg are considered long muscles, in that they stretch great distances. As these muscles contract and relax, they move skeletal bones to create movement of the body. Smaller muscles help the larger muscles, stabilize joints, help rotate joints, and facilitate other fine-tuned movements.

[snjarhvitr]

Thank you!!! This explanation is ten times easier to understand than the roundabout way my book is explaining.

[jenniferellsworth]

Thank you, Scientist Cindy. I teach anatomy, and the explanation in Marieb's text is that "eccentric contraction is less well understood". This drives me crazy as the answer is so simple. Fewer crossbridges allows tension in the muscle that can be overcome by gravity resulting in greater control across the joint when lowering a heavy load...like the body itself. Much appreciated. I will direct my students here who have questions about eccentric contraction.

[ratfest]

Thanks i was just looking over my notes for my unit 2 PE test tomorrow and needed to look over this topic. this really helped!! Thanks

[garzascreek]

I love your animations. And kudos on knowing how to pronounce _eccentric_ (a rarity on YouTube).

[putriayuwulansari]

I like the way you explain it, thanks!

[denniswilliams]

Thank you, this video helped me study!

[jaredfeatherston]

You begin by saying that in Isotonic muscle contraction, tension remains constant, but then when describing the two types of isotonic muscle contraction you say that tension increases in concentric contractions and decreases in eccentric contractions. This is contradictory. Does tension change or does it stay the same in isotonic contractions?

[zi]

Super video! I applauded for NZ$50.00 👏👏👏👏

[anastasijanikolic]

This was a great video, thank you a lot!

[aashumivora]

Thank you..was of great help while studying❤️

[marykateotto]

I am not familiar with a lot of the terms used in this video and so I found it too much to take in all at once. I think I would have liked it better if the images had been introduced and then the nomenclature. Also, I wish there has been a bit more breaks in-between the segments as I felt like they were rushed, and even seem to make the speaker hurry through the verbal descriptions.

[obcolik]

when biceps are concentrically contracting do triceps eccentrically contracting at the same time?

[meenakshibisht]

Why tension not increase as length shortened?!

[Khubsuraat]

Thank u❤️❤️❤️❤️❤️❤️ for d session ...so helpful

[kevinvigi.mathew]

what is combination of isometric and isotonic called?

[raoulfulgos]

Good vid, I'd ditch this music tho.

[ylva]

2:02 not true, in isometric contraction the muscle tension changes while the lengths stays constant

[thetruesquad]

I used this video for a presentation so I was watching it for 30 minutes