"Muscle Action" vs. "Contraction" — The Terminology Argument
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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 (Positive) Muscle Action — shortening action.
- Eccentric (Negative) Muscle Action — lengthening action.
- Isometric (Static) Muscle Action — no-length-change action.
- Classification of Exercise and Muscle Action Types (Dynamic vs. Static) — dynamic vs. static table.
- Positive and Negative Resistance — positive/negative resistance phrasing of the same idea.
Sources
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