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Fiber architecture

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Fiber architecture Quantification of muscle structure Relationship to functional capacity Muscle as one big sarcomere Independent fibers/fascicles – PowerPoint PPT presentation

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Title: Fiber architecture


1
Fiber architecture
  • Quantification of muscle structure
  • Relationship to functional capacity
  • Muscle as one big sarcomere
  • Independent fibers/fascicles

2
Terminology
  • Attachments
  • Origin
  • Insertion
  • Muscle belly
  • Aponeurosis (internal tendon)
  • Fascicle (Perimysium)
  • Compartment
  • Pennation

3
Connective tissue layers
  • Endomysium
  • Perimysium
  • Epimysium

Purslow Trotter 1994
4
Muscles are 3-D structures
5
Structural definition
  • Qualitative
  • Epimysium
  • Discrete tendon
  • Insertion (gastroc)
  • Origin (extensor digiti longus)
  • Easy to separate
  • Electrophysiological
  • Common nerve
  • Common reflex

6
3-D structures
  • Curved (centroid) paths
  • Curved fiber paths
  • Distributed attachments
  • Varying fascicle length

7
Categorizing
  • Pennation
  • Longitudinal
  • Unipennate
  • Bipennate
  • Multipennate
  • Approximation
  • Fascicle length
  • Force capacity

8
Historical
  • Stensen (1660)
  • Borelli (1680)
  • Gosch (1880)

9
Idealized muscles
  • Muscle mass (M)
  • Muscle length (Lm)
  • Fascicle length (Lf)
  • Pennation angle (q)
  • Physiological cross sectional area (PCSA)

10
The Gans Bock Model
  • Vastus Intermedius
  • Identical facsicles
  • Originate directly from bone
  • Insert into tendon that lies parallel to bone
  • Geometrical constraints
  • Tendon moves parallel to bone
  • Constant volume
  • 2-D approximation
  • No change into the paper
  • ?Constant area

11
Force capacity
d
  • Physiological cross-sectional area
  • Sum fascicles perpendicular to axis
  • Not measurable
  • Fm Ts PCSA
  • Prism approximation
  • Volume bd
  • B sin(q) V/Lf
  • PCSA V/ Lf M/r/Lf
  • Project force to tendon
  • Ft Fm cos(q) TsM/r/Lf cos(q)

b
q
Fm
Lf
PCSA
Ft
12
Test PCSA
  • Spector al., 1980
  • Cat soleus and medial gastrocnemius
  • Powell al., 1984
  • Guinnea pig 8 calf muscles

Powell
Spector
130
41
Predicted PCSA (?)
Predicted Ft (o)
6
0.7
Relative measure
Measured force
13
Are pennate muscles strong?
  • Ft TsM/r/Lf cos(q)
  • cos(q) is always 1
  • Ft Fm
  • Fiber packing
  • Series sarcomeres (A1, F1)
  • Parallel sarcomeres (A6, F6)
  • Pennate sarcomeres (A 6, F5.2)

14
Length change
d
  • Fiber shortens from f?f1
  • Rotates from q ? q1
  • bd constant
  • bfsin(q) bf1sin(q1)
  • h fcos(q)-f1cos(q1)
  • Fractional shortening in muscle is greater than
    the fractional shortening of fascicles
  • If the fascicles rotate much
  • eg 15 fibers, fascicle shorten 25?muscle 27

f1
b
h
q
q1
f
15
Operating range
  • Muscle can shorten 50 (Weber, 1850)
  • Operating range proportional to length
  • Spasticity
  • Reduced mobility (Crawford, 1954)
  • Length-tension relationship
  • Useful range strongly dependent on Lo
  • Pennate fibers shorten less than their muscle

16
Velocity
  • Force-velocity relationship
  • Shortening muscle produces less force
  • Power force speed
  • Acceleration
  • Architecture and biochemistry influence Vmax
  • Fiber type 2x
  • Fiber length 12x

17
Other Geometries
  • Point origin, point insertion
  • Elastic aponeurosis
  • Increase length with force
  • Vm Va Vf
  • Multipennate muscles

Cos(a-q) Cos(a)
Cos(q) Cos(a)
18
Other subdivisions
  • Multiple bellies
  • Digit flexors/extensors
  • Biceps/Triceps
  • Multiple discrete attachments
  • Compartments
  • Most large muscles
  • Internal connective tissue
  • Internal nerve branches

19
Multiple bellies
  • Rat EDL
  • 4 insertion tendons
  • 2 nerve branches
  • Glycogen depletion
  • Discrete branch territories
  • Mixing at ventral root

Balice-Gordon Thompson 1988
20
Compartments
  • Cat lateral gastrocnemius
  • Dense internal connective tissue
  • Surface texture
  • Internal nerve branches

21
LG Compartments
  • Motor unit
  • Axoninnervated fibers
  • Constrained to compartment

English Weeks, 1984
22
Neural view
  • Does NS use the same divisions as anatomists?
  • Careful training can control single motoneuron
  • Behavioral recruitment spans muscles
  • Mechanical tuning
  • Training

23
Anatomical vs neural division
  • Muscle
  • Easily separated
  • Separately innervated
  • Multi-belly
  • Partly separable
  • Slight overlap of nerve territories
  • Compartment
  • Inseparable
  • Slight overlap of nerve territories

24
Fibers and fascicles
  • Rodents
  • Fiber fascicle
  • Easiest experimental model
  • Small animals
  • Fascicle 5-10 cm
  • Fiber 1-2 cm (conduction velocity 2-5 m/s)

25
Motor unit distribution
Fibers innervated by single MN are near one MEP
band
  • MU localized longitudinal

Motor endplates in sternomanibularis
Smits et al., 1994
Purslow Trotter, 1994
26
3-D reconstruction
  • Relatively straight fibers
  • Taper-in, taper-out

Ounjian et al., 1991
27
Mechanical independence
  • Bag of spaghetti model
  • Independent muscle/belly/compartment/fiber
  • Little force sharing
  • Fiber composite model
  • Adjacent structures coupled elastically
  • Lateral force transmission

28
Fiber level force transmission
  • Sybil Street, 1983
  • Frog sartorius
  • All but one fiber removed from half muscle
  • Anchor remaining fiber ends
  • Anchor segment and clot
  • Same force

29
Belly level force transmission
  • Huijing al., 2002
  • Rat EDL
  • Separate digit tendons
  • Cut one-by-one (TT)
  • Pull bellies apart (MT)
  • Little force change with tenotomy only

30
Muscle level force transmission
  • Maas al., 2001
  • Rat TA and EDL
  • Separate control of muscle lengths
  • Measure both EDL origininsert F
  • 10 EDL-TA trans

31
Summary
  • Architectural quantification M, Lm, Lf, q
  • Estimates of force production PCSA (Fm), Ft
  • Simple models are pretty good
  • Sub-muscular structures compartments
  • Neural structure is not the same as muscle
    structure
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