biomechanics of human skeletal muscle mohd yusof baharuddin bbiomedeng(um) mbiomedeng(melbourne)...
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BIOMECHANICS of HUMAN SKELETAL
MUSCLE
Mohd Yusof BaharuddinBBiomedEng(UM)
MBiomedEng(Melbourne)
ENT 214 Biomechanics
Picture from MisterBisson Flickr pages
Extensibility & Elasticity
What is extensibility? Ability to stretch or to increase in length
How about elasticity? Ability to return to normal length after stretch
Figure from http://www.flashplayer.com/forum/showthread.php?t=20485
Elastic Behaviour
1. Parallel elastic component (PEC) Muscle membrane Supply resistance when muscle is passively stretched
2. Series elastic component (SEC) Tendons Act as spring to store elastic energy
3. Contractile component (CC) Muscle property enabling tension by stimulated
muscle fibers
Muscle Tissue Behavioral Properties
Irritabilityability to respond to a stimulus
Ability to develop tension the contractile component of muscle
function
Structural Organization of Skeletal Muscle
What is a muscle fiber?Because of threadlike shapesingle muscle cell surrounded by a
membrane called the sarcolemma and containing specialized cytoplasm called sarcoplasm
Skeletal Muscle
Silverthorn, Human Physiology,Benjamin-Cummings, ISBN 0-321-22687-9, Fig. 12-3, p. 392
Skeletal muscle
Silverthorn, Human Physiology,Benjamin-Cummings, ISBN 0-321-22687-9, Fig. 12-1a, p. 390
Muscle fibers
some fibers run the entire length of a muscle; others are shorter
skeletal muscle fibers grow in both length and diameter from birth through adulthood
fiber diameter can be increased through resistance training
Motor unit
single motor neuron and all fibers it innervates
considered the functional unit of the neuromuscular system
There are 2 types Fast twitch (FT) Slow twitch (ST)
Structural Organization of Skeletal Muscle
Fast twitch (FT) fibers both reach peak tension and relax more quickly than slow twitch (ST) fibers.
Peak tension is typically greater for FT than for ST fibers.
Tw
itch
Ten
sion
Time
FT ST
Skeletal Muscle Fiber Characteristics
TYPE IIAType I Fast-Twitch Type IIB
Slow-Twitch Oxidative Fast-Twitch Oxidative Glycolytic Glycolytic
CHARACTERISTIC (SO) (FOG) (FG)Contraction Speed slow fast fast
Fatigue rate slow intermediate fast
Diameter small intermediate large
ATPase concentration low high high
Mitochondrial high high lowconcentrationGlycolytic enzyme low intermediate highconcentration
Fiber architecture
There are 2 types of fiber architecture parallel fiber arrangement
fibers are roughly parallel to the longitudinal axis of the muscle
example: sartorius, rectus abdominis, biseps brachii
pennate fiber arrangement short fibers attach to one or more tendons within the
muscle example: tibialis posterior, rectus femoris, deltoid
Fiber architecture (cont’d)
parallel fiber arrangement Muscle become shorten due to fiber shortening
pennate fiber arrangement When muscle shorten, they rotate about their
tendon attachment This will increase the angle of pennation Greater angle of pennation will induced smaller
amount of effective force
Sample Problem 1
Ft
Ffα
How much force is exerted by tendon of pennate muscle when tension in fiber is 100 N, given that the angle of pennation is 60 degree.
Recruitment of Motor Units (MU)
Slow twitch (ST) fibers are easier to activate than fast twitch (FT) fibers
ST fibers are always recruited first Increasing speed, force, or duration of
movement involves progressive recruitment of MUs with higher and higher activation thresholds
Terms used to describe muscle contractions
concentric: involving shortening eccentric: involving lengthening isometric: involving no change
Muscles Roles
agonist: acts to cause a movement antagonist: acts to slow or stop a movement stabilizer: acts to stabilize a body part
against some other force neutralizer: acts to eliminate an unwanted
action produced by an agonist
Two Joint and Multijoint Muscles
active insufficiency: failure to produce force when slack
passive insufficiency: restriction of joint range
of motion when fully stretched
Active Insufficiency
Failure to produce force when muscles are slack (decreased ability to form a fist with the wrist in flexion)
Passive insufficiency
Restriction of joint range of motion when muscles are fully stretched (decreased ROM for wrist extension with the fingers extended)
Factors Affecting Muscular Force Generation
The force-velocity relationship for muscle tissue:
When resistance (force) is negligible,
muscle contracts with maximal
velocity.
Velocity
For
ce(Low resistance, high contraction velocity)
Force – Velocity Relationship
The force-velocity relationship for
muscle tissue: As the load increases,
concentric contraction velocity
slows to zero at isometric
maximum.Velocity
For
ce
isometric maximum
Length – Tension Relationship
The length-tension relationship: Tension
present in a stretched muscle is the sum of the active tension provided
by the muscle fibers and the passive tension
provided by the tendons and membranes.
Te
nsio
n
Length (% of resting length)50 100 150
Active Tension
Passive Tension
Total Tension
The length-tension relationship: Tension
present in a stretched muscle is the sum of the active tension provided
by the muscle fibers and the passive tension
provided by the tendons and membranes.
Te
nsio
n
Length (% of resting length)50 100 150
Active Tension
Passive Tension
Total Tension
Force – Time Relationship
What is electromechanical delay (EMD)?
EMD is the time between arrival of a neural stimulus and tension development by the muscle
Time needed for muscles reached maximum isometric is 0.2 - 1 second after EMD
Myoelectric activity
Force
Electromechanical delayStimulus
How do we measure muscular strength?
The component of muscle force that produces torque (Ft) at the joint is directed perpendicular to the attached bone.
Ft Ft
Sample Problem 2
α
How much tork is produced at the elbow by biceps brachii inserting at an angle 60 degree on the radius when tension in the muscle is 400 N?
Factors affect muscular strength
tension-generating capability of the muscle tissue, which is in turn affected by:
– muscle cross-sectional area– training state of muscle
Factors affect muscular strength
moment arms of the muscles crossing the joint (mechanical advantage), in turn affected by:
– distance between muscle attachment to bone and joint center
– angle of the muscle’s attachment to bone
Effects for differences angle
The mechanical advantage of the biceps bracchi is maximum when the elbow is at approximately 90 degrees (A), because 100% of muscle force is acting to rotate the radius. As the joint angle increases (B)or decreases (C) from 90 degrees, the mechanical advantage ofthe muscle is lessened because more and more of the force is pullingthe radius toward or away from the elbow rather than contributing to forearm rotation.
CA B
Muscle Power
the product of muscular force and the velocity of muscle shortening
the rate of torque production at a joint the product of net torque and angular
velocity at a joint
Muscular Power
The general shapes of the force-velocity and power-velocity curves for skeletal muscle.
For
ce
Velocity
Pow
er
Power-VelocityForce-Velocity
Muscular Endurance
the ability of muscle to exert tension over a
period of time
the opposite of muscle fatigability
Effect of muscle temperature(Warm up) cont’d
With warm-up, there is a shift to the right in
the force-velocity curve, with higher
maximum isometric tension and higher
maximum velocity of shortening possible at
a given load.Velocity
For
ce
Normal body temperature
Elevated body temperature
Summary
1. Basic behavioral properties of the muscle unit
2. Relationships of fiber types and architecture to muscle function
3. Skeletal muscles function to produce coordinated movement of the human body
4. Effects of the force-velocity and length-tension relationships and EMD on muscle function
5. Muscular strength, power, and endurance