muscle
one of the contractile organs of the body
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an agent to recognise an individual muscle organ, assess its capacity and condition, and identify actions consistent with its anatomical role and observed limits.
A muscle is an anatomical organ composed of elongated contractile cells (myocytes) bound by connective-tissue sheaths into a unit that generates force and shortening, or resists stretch, under neural or myogenic control, typically acting through tendons or aponeuroses on a skeleton, viscus, or skin.
It can be Locate and identify the muscle and distinguish it from adjacent muscles or other tissues.; Relate its attachments and activation to a specified movement or stabilising task.; Select observations that address uncertainty about its structure, activation or mechanical contribution.; Compare its condition and performance across sessions using matched measurement conditions.; Assess a proposed loading or measurement action against recorded limits and required professional authorisation.; Flag observations that require further assessment before an action can be justified..
Distinguishing features
An individual muscle has an anatomical identity and boundary; a muscle group denotes several such organs acting or described together.
A muscle contains contractile tissue organised as an organ; a tendon primarily transmits force and is not itself the contractile organ.
A tissue sample qualifies as material from a muscle, but does not establish the identity or extent of the whole organ.
A named head or compartment must be checked against anatomical convention before being treated as a separate muscle.
Contractile tissue within a heart or hollow-organ wall does not by itself establish a separately registered muscle organ.
Scope
+ Muscle identity, species, anatomical location, laterality and constituent heads or compartments
+ Fascicle organisation, attachment interfaces and relationships to neighbouring structures
+ Activation, contraction and force transmission under specified conditions
+ Capacity, fatigue, recovery and adaptation over time
+ Local integrity, symptoms and constraints relevant to observation or loading
- Muscle tissue or individual fibres studied independently of an identified muscle organ
- Whole-body fitness, exercise programmes and coordinated movement performance
- Independent models of tendons, bones, joints, nerves and blood vessels
- The heart as a complete pumping organ and other organs containing muscular walls
- Systemic diseases, clinical diagnoses and treatment plans
Characteristics
- Anatomical identity
- Species-qualified anatomical name, terminology reference and recognised variants Establishes which organ is represented and prevents similarly named structures from being conflated.
- Location and laterality
- Body region; left, right, midline, unpaired or unresolved Distinguishes individual instances and anchors observations to the correct site.
- Attachments and force-transmission interfaces
- Identified attachment structures and interfaces, including tendon, aponeurosis or direct attachment where applicable Connects contraction to the structures on which the muscle can act.
- Fascicle architecture
- Fascicle length in mm and pennation angle in degrees, with site, posture and method Helps interpret mechanical behaviour and changes in muscle structure.
- Muscle size
- Volume in cm³ or explicitly defined cross-sectional area in cm², with method and sampling location Supports comparison over time without treating size as a direct measurement of strength.
- Mechanical output
- Muscle force in N when measured or estimated; joint torque in N·m recorded as a contextual proxy Records mechanical contribution while distinguishing individual-muscle estimates from combined joint output.
- Activation
- Method-specific signal, such as EMG amplitude in mV or a stated normalised percentage Describes evidence of activation without equating electrical activity with force.
- Contraction behaviour
- Active shortening, active lengthening, active near-constant length, inactive or unresolved; specify observation scale Distinguishes how the muscle is operating during a particular task.
- Local condition
- Observed integrity, symptoms, fatigue and recovery status, each with time and evidence Makes limitations and changes visible without converting uncertain observations into diagnoses.
Analytical facets
- substance
- living
- origin
- natural
- agency
- inert
- mobility
- not-applicable
- scale
- not-applicable
- affordances
- observable
Also called
+158
Where this came from
oewn:2024 · CC BY 4.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Muscle identity and extent Establishes which muscle organ is represented and where its anatomical ownership ends.
Muscle names, heads and tissue boundaries can otherwise produce duplicate or incorrectly scoped organ records.
Anatomical identification
Resolves the muscle's name within a species and body location.
Species-qualified muscle identity
Records anatomical designation, laterality and variants with evidence for the identification.
- Which species, anatomical name, body region and side identify this muscle? definition
- Which anatomical reference or direct observation supports that identification? provenance
Organ boundaries
Separates the muscle organ from its subdivisions and neighbouring structures.
Heads, compartments and interfaces
Identifies included subdivisions and the interfaces through which adjacent structures relate to the muscle.
- Which heads, bellies or compartments belong to this muscle rather than separate muscle organs? boundary
- Where does this muscle's represented extent meet tendons, aponeuroses, fascia or neighbouring muscles? boundary
Architecture and force transmission Connects internal organisation and attachments to the muscle's mechanical contribution.
A muscle's action depends on its architecture, attachment geometry and task configuration.
Contractile architecture
Describes the size and arrangement of the contractile structure under stated conditions.
Fascicle and size observations
Records muscle dimensions and fascicle geometry while preserving the measurement context.
- What muscle volume, cross-sectional area, fascicle length or pennation angle has been measured, and at which site? measurement
- What posture, activation condition and measurement method accompanied those observations? provenance
Attachment mechanics
Describes the path by which contraction affects attached structures.
Task-specific mechanical contribution
Relates attachment geometry to movement or stabilisation without assuming a fixed action in every posture.
- Through which attachments does this muscle transmit force, and which structures can it move or stabilise? definition
- For the specified posture and task, what evidence supports its line of action, moment arm where relevant and mechanical contribution? measurement
Activation and contraction Records how the muscle is recruited and what mechanical behaviour accompanies that recruitment.
Activation signals, tissue motion and force are different observations that must be interpreted together.
Innervation and recruitment
Links the muscle to its neural supply and evidence of task-dependent activation.
Activation evidence
Records innervation relationships and activation observations with their attribution limits.
- Which nerve supply is documented for this muscle or its separately innervated compartments? provenance
- How was activation observed, normalised and distinguished from signals originating in adjacent muscles? measurement
Contraction and output
Distinguishes activation, length change and output during a defined task.
Observed contractile behaviour
Records whether the active muscle shortens, lengthens or maintains approximately constant length, and how output is attributed.
- During the task, what length change is observed at the fascicle, muscle belly or muscle-tendon unit level? measurement
- Is the reported output an individual-muscle force measurement, a model estimate or joint torque involving several muscles? boundary
Capacity, fatigue and adaptation Tracks task-specific capacity and its change with exertion, recovery and repeated exposure.
A muscle's current ability cannot be inferred from its identity or size alone, and varies with testing conditions and recent use.
Task-specific capacity
Characterises the performance the muscle contributes to under a defined protocol.
Capacity and fatigability
Records initial output and its change during repeated or sustained effort.
- What output or task duration is supported under a stated load, posture, contraction mode and protocol? measurement
- How does output change during exertion, and what limits attribution of that change to this muscle? measurement
Recovery and longitudinal change
Separates short-term recovery observations from longer-term changes in structure or capacity.
Response to loading history
Relates repeated observations to documented use, unloading and recovery intervals without assuming causation.
- What recent loading or unloading preceded the observation, and how much recovery time elapsed? provenance
- Under comparable conditions, what changes in size, output or fatigability exceed the method's uncertainty? measurement
Integrity and action constraints Connects evidence about local condition to the justification and limits of proposed actions.
Observed symptoms and structural findings may affect what can be measured or loaded, but neither alone establishes a diagnosis or permission to intervene.
Local condition evidence
Records symptoms and structural observations with location, timing and uncertainty.
Symptoms and tissue integrity
Distinguishes reported experience from examination or imaging findings and preserves uncertain localisation.
- What pain, tenderness, swelling or functional change is reported, where is it located and when does it occur? measurement
- What examination or imaging evidence concerns this muscle's integrity, and how securely is the finding localised to it? provenance
Permitted observation and loading
Makes the prerequisites and stopping conditions for a proposed muscle-related action explicit.
Action prerequisites and limits
Records the evidence, authority and observed limits relevant to measurement, loading or referral for assessment.
- For the proposed measurement or loading action, what recorded restrictions, consent or professional authorisation apply? action
- What missing evidence or observed response requires the action to be deferred, stopped or referred for further assessment? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- skeletal (striated, voluntary, typically attached to bone)
- cardiac (striated, involuntary myocardium)
- smooth (non-striated, involuntary, viscera and vessels)
- named skeletal muscle as an organ (e.g. biceps brachii, with origin, insertion, innervation)
- muscle fascicle / belly as a morphological part
- sphincter versus dilator / antagonistic pairs
- tonic versus phasic fibre-type dominance (type I slow-oxidative vs type II fast)
- extraocular, laryngeal and other specialised striated muscles
- Which of these kinds and varieties hold for the sense of muscle this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q7365 - item 'muscle' (anatomical structure); cardiac and smooth muscle have distinct items.
- FMA - FMA:5022 - Muscle organ; individual named muscles have their own FMA identifiers.
- UBERON - UBERON:0001630 - muscle organ; contrast UBERON:0001134 muscle tissue.
- TA2 - TA2 A04.* (muscle chapter) - Latin/English official names; each named muscle has a TA2 code in chapter A04.
- SNOMED CT - 71616004 |Skeletal muscle structure (body structure)| and related hierarchy - Clinical body-structure codes; not a single code for all muscle kinds.
- MeSH - D009132 - Muscles; narrower headings for Muscle, Skeletal; Myocardium; Muscle, Smooth.
- Which of these identifiers and schemes hold for the sense of muscle this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- IFAA / FIPAT Terminologia Anatomica (TA2) - official human anatomical names for muscles
- ISO 24156-1 / ISO/IEC 11179-style data-element practice is not muscle-specific; anatomical coding in EHR is typically SNOMED CT, ICD-11 extension codes, or LOINC for lab tests on muscle
- WHO ICD-11 - diseases of the musculoskeletal system and muscle (chapter 15) and myopathies; not a naming standard for the organ itself
- ILO / national OSH regulations (e.g. EU Machinery Directive risk assessment, OSHA / HSE manual-handling regs) govern exposure to muscle overload at work, not the organ as a product
- WADA Prohibited List - governs substances that act on muscle (anabolic agents), not the tissue as a commodity
- Human tissue and transplant law (e.g. EU Tissues and Cells Directives, US Uniform Anatomical Gift Act) when muscle is procured as tissue
- Which of these standards and regulation hold for the sense of muscle this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Clinical examination and imaging (inspection, MRC power grades, EMG, MRI, ultrasound) to localise lesions of named muscles
- Surgical landmarks, tendon transfers, flap harvest (e.g. latissimus dorsi, gracilis) and intramuscular injection sites
- Histopathology and biopsy of skeletal muscle in myopathy and inflammatory myositis work-ups
- Sports science and rehabilitation: strength, hypertrophy, and return-to-play testing of muscle groups
- Meat and food: skeletal muscle as the principal edible tissue of livestock (but then treated as a food commodity, not an anatomical organ)
- Research models: isolated muscle preparations, cultured myotubes, and in vivo torque/force measurement
- Which of these real-world use hold for the sense of muscle this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- maximum voluntary isometric force (or joint torque as a proxy) - varies by muscle and subject; e.g. adult knee-extensor MVC often ~100-300 N·m - N or N·m
- physiological cross-sectional area (PCSA) - from <1 cm² (small hand muscles) to tens of cm² (quadriceps) - cm²
- fibre length / pennation angle - fibre length millimetres to tens of centimetres; pennation typically 0-30° - mm and °
- muscle mass or volume - a named human muscle from a few grams to >1 kg; total skeletal muscle ~30-40% of adult body mass - g or cm³
- electromyographic activity - surface EMG amplitudes typically tens to a few thousand µV depending on electrode and contraction - µV or % MVC
- serum creatine kinase (systemic marker of muscle injury, not a property of one organ) - reference roughly 30-200 U/L in adults, assay-dependent; much higher after damage - U/L
- Which of these typical measurements hold for the sense of muscle this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Strain, tear, or rupture of muscle belly or myotendinous junction
- Contusion, compartment syndrome, and crush-related rhabdomyolysis with acute kidney injury
- Denervation atrophy, disuse atrophy, sarcopenia, and cachexia
- Inherited and acquired myopathies, muscular dystrophies, inflammatory myositis, and channelopathies (cramp, paralysis)
- Contracture, fibrosis, heterotopic ossification, and fatty replacement after injury or ischaemia
- Iatrogenic injury (intramuscular injection neuropathy, tourniquet ischaemia, surgical denervation)
- Cardiac muscle: ischaemia, infarction, arrhythmia, pump failure (neighbouring organ-system hazard, not skeletal)
- Which of these failure modes and hazards hold for the sense of muscle this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Eponyms versus descriptive names: many muscles still taught under Latin TA names in Europe and under Anglicised or eponymous names in some clinical English (e.g. musculus levator palpebrae superioris vs levator of the upper eyelid)
- Veterinary and comparative anatomy use homologous names that do not map 1:1 to human TA2 (e.g. animal 'cutaneous trunci', variable rhomboideus parts)
- Food-animal butchery nomenclature (primal cuts) does not coincide with anatomical muscle names
- Traditional Chinese medicine and some folk anatomies group 'sinew' / 'flesh' without the organ-level muscle concept of TA/FMA
- Which of these regional variation hold for the sense of muscle this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- muscle tissue (as a tissue type) - Tissue (myocytes plus endomysium) can exist as a portion of an organ; FMA/UBERON treat muscle organ as the named, encapsulated contractile organ with origin, insertion and innervation, not the tissue class.
- tendon / aponeurosis - Dense regular connective tissue transmitting force; continuous with muscle at the myotendinous junction but not contractile; distinguished histologically (collagen vs myofibres) and by imaging.
- ligament - Bone-to-bone connective tissue; no contractile fibres; origin/insertion pattern and lack of motor innervation separate it from muscle.
- fascia / epimysium - Connective-tissue envelope or plane around muscle; may be dissected from the contractile belly; not itself an independent contractile organ.
- nerve (peripheral nerve entering a muscle) - Conducts action potentials; stimulation or EMG source vs sink; a muscle without its nerve still has contractile tissue but is paralysed.
- smooth-muscle-containing viscus (e.g. bladder wall) versus a named smooth-muscle organ - Most 'smooth muscle' is a tissue layer of another organ; a sphincter named as a muscle (e.g. sphincter pupillae) is treated as a muscle organ only when anatomy lists it as such.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of muscle this model covers, and on what evidence? provenance
Sources
- Terminologia Anatomica, 2nd edition (TA2) - Official IFAA nomenclature for muscles as organs and the skeletal/cardiac/smooth partition used in human anatomy.
- Foundational Model of Anatomy: Muscle organ (FMA 5022) and related classes - Formal organ-level definition of muscle as a contractile anatomical structure distinct from muscle tissue.
- UBERON: muscle organ (UBERON:0001630) - Cross-species ontology class for a contractile organ, linking vertebrate and some invertebrate usage.
- Gray's Anatomy: The Anatomical Basis of Clinical Practice - Standard clinical description of muscle as an organ, architecture (epimysium-perimysium-endomysium), innervation and actions.
What the second pass must settle
- Does the registry intend this entry to cover only individually named skeletal muscle organs, or also anatomically discrete non-skeletal contractile structures?
- Which species-specific anatomical authorities should determine whether a head, belly, sphincter or compartment is a separate muscle organ?
- Where should ownership of intramuscular tendons, aponeuroses and attachment regions end when neighbouring models also represent them?
- Which measurement methods support defensible attribution of force and fatigue to an individual muscle, and how should uncertainty be represented?
- Which task-specific evidence and qualified authority are required to turn observed muscle condition into an actionable loading constraint?