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"Muscle Action" vs. "Contraction" — The Terminology Argument

Evidence-grounded — sourced from Fysiqal's fitness knowledge graph· 2 min read
muscle-actionterminologyconcentriceccentricisometric

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In one line

Because a muscle can shorten, hold, or lengthen, calling every state a "contraction" is misleading — so the term "muscle action" is proposed instead.

Detail

Muscle action is defined as the state of activity of a muscle (Fleck & Kraemer, 1997). Three states are distinguished:

  • Concentric action: one in which the ends of the muscle are drawn closer together.
  • Isometric action: one in which the ends of the muscle are prevented from drawing closer together, with no change in length.
  • Eccentric action: one in which a force external to the muscle overcomes the muscle force and the ends of the muscle are drawn further apart.

The terminology argument: To describe the state of activity of a muscle as a "contraction" when the muscle may be shortening, maintaining the same length, or being lengthened seems inappropriate. Therefore the term "muscle action" has been proposed to describe the result of skeletal muscle force development interacting with external forces that affect the body parts of the exercising human.

A related corollary appears in the source's treatment of negative/eccentric resistance: "There is no such thing as 'Eccentric Contractions'" — because a lengthening muscle is not, strictly, contracting.

Key facts

  • "Muscle action" is preferred over "contraction" because muscles can shorten, hold length, or lengthen.
  • Three actions: concentric (ends closer), isometric (no length change), eccentric (ends drawn apart).
  • "Muscle action" = the result of skeletal muscle force development interacting with external forces.
  • Corollary: "there is no such thing as 'eccentric contractions'."

Connections

  • concentric-action — shortening action.
  • eccentric-action — lengthening action.
  • isometric-action — no-length-change action.
  • exercise-muscle-action-classification — dynamic vs. static table.
  • positive-negative-resistance — positive/negative resistance phrasing of the same idea.
SourceReference manual
p.76p.368
Cited authorities in source: Fleck & Kraemer (1997).
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Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.

Explore related topics

Atlas Connections

Concentric (Positive) Muscle ActionClosely related
The lifting phase — a dynamic action where the whole muscle shortens, its ends draw closer together, and joint movement occurs.
Eccentric (Negative) Muscle ActionClosely related
The lowering phase — a dynamic action where an external force overcomes the muscle and forcibly lengthens it; the strongest action and the chief cause of DOMS.
Classification of Exercise and Muscle Action Types (Dynamic vs. Static)Closely related
Exercise is either dynamic (concentric = shortens, eccentric = lengthens) or static (isometric = no change), mapped to what happens to muscle length.
Isometric (Static) Muscle ActionClosely related
A static action where the muscle develops force but its ends are prevented from drawing closer together — no change in length, no joint movement.
Positive and Negative ResistanceClosely related
"Positive" is the concentric (shortening) phase and "negative" is the eccentric (lengthening) phase — the lifter's-eye names for the two dynamic actions.