Chapter 6 The Biomechanics of Human Skeletal Muscle Basic Biomechanics, 6 th edition By Susan J....
-
Upload
gillian-cobb -
Category
Documents
-
view
238 -
download
2
Transcript of Chapter 6 The Biomechanics of Human Skeletal Muscle Basic Biomechanics, 6 th edition By Susan J....
Chapter 6
The Biomechanics of Human Skeletal
MuscleBasic Biomechanics, 6th edition
By Susan J. Hall, Ph.D.
© 2012 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill/Irwin
6-2
Behavioral Properties of the Musculotendinous Unit
1) extensibility: ability to be stretched or to increase in length
2) elasticity: ability to return to normal resting length following a stretch
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-3
Behavioral Properties of the Musculotendinous Unit
Components of elasticity:
• parallel elastic component - passive elasticity derived from
muscle membranes
• series elastic component - passive elasticity derived from
tendons when a tensed muscle is stretched
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-4
Behavioral Properties of the Musculotendinous Unit
Parallel Elastic Component
Series Elastic ComponentContractile
Component
From a mechanical perspective, the musculotendinous unit behaves as a contractile component (muscle fibers) in parallel with one elastic component (muscle membranes) and in series with another elastic component (tendons).
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-5
What is the stretch-shortening cycle?
• eccentric contraction (in which the muscle is actively stretched)
followed immediately by concentric contraction• Can you think of examples?
Behavioral Properties of the Musculotendinous Unit
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-6
Behavioral Properties of the Musculotendinous Unit
3) irritability: ability to respond to a stimulus
4) ability to develop tension: the contractile component of muscle function
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-7
Structural Organization of Skeletal Muscle
What is a muscle fiber?
(single muscle cell surrounded by a membrane called the sarcolemma and containing specialized cytoplasm called sarcoplasm)
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-8
Structural Organization of Skeletal Muscle
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
Sarcolemma
6-9
Structural Organization of Skeletal Muscle
What do we know about 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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-10
Structural Organization of Skeletal Muscle
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
Sarcomere
The sarcomere is the basic structural unit of the muscle
fiber. The alternating dark and light bands give muscle
its striated appearance. The A bands contain thick, rough
myosin filaments surrounded by six thin, smooth actin
filaments. The I bands contain only thin actin filaments.
6-11
Structural Organization of Skeletal Muscle
What is a motor unit?
• single motor neuron and all fibers it innervates
• considered the functional unit of the neuromuscular system
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-12
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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-13
Skeletal Muscle Fiber Characteristics TYPE IIA
Type I Fast-Twitch Type IIB Slow-Twitch Oxidative Fast-Twitch
Oxidative Glycolytic GlycolyticCHARACTERISTIC (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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-14
Structural Organization of Skeletal Muscle
How are muscle fibers organized?
• parallel fiber arrangement: fibers are roughly parallel to the longitudinal axis of the muscle; examples are?
• pennate fiber arrangement: short fibers attach to one or more tendons within the muscle; examples?
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-15
Structural Organization of Skeletal Muscle
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
Parallel fiber arrangements Pennate fiber arrangements
6-16
Structural Organization of Skeletal Muscle
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
Relaxed With tension development
The angle of pennation increases as tension progressively increases in the muscle fibers.
6-17
Skeletal Muscle Function
How are motor units (MUs) recruited?
• 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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-18
Skeletal Muscle Function
What terms are used to describe muscle contractions based on change in muscle length?
• concentric: involving shortening
• eccentric: involving lengthening
• isometric: involving no change
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-19
Skeletal Muscle Function
What roles are assumed by muscles?
• 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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-20
Skeletal Muscle Function
What are disadvantages associated with muscles that cross more than one joint?
• active insufficiency: failure to produce force when slack • passive insufficiency: restriction of joint
range of motion when fully stretched
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-21
Skeletal Muscle Function
active insufficiency: failure to produce force when muscles are slack (decreased ability to form a fist with the wrist in flexion)
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-22
Skeletal Muscle Function
passive insufficiency: restriction of joint range of motion when muscles are fully stretched (decreased ROM for wrist extension with the fingers extended)
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-23
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)
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-24
Factors Affecting Muscular Force Generation
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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-25
Factors Affecting Muscular Force Generation
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.
Ten
sion
Length (% of resting length)50 100 150
Active Tension
Passive Tension
Total Tension
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-26
Factors Affecting Muscular Force Generation
What is electromechanical delay?
(time between arrival of a neural stimulus and tension development by the muscle)
Myoelectric activity
Force
Electromechanical delayStimulus
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-27
Muscular Strength, Power and Endurance
How do we measure muscular strength?
(the amount of torque a muscle group can generate at a joint)
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-28
Muscular Strength, Power and Endurance
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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-29
Muscular Strength, Power and Endurance
What 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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-30
Muscular Strength, Power and Endurance
What 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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-31
Skeletal Muscle Function
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
Torque produced by a muscle (Tm) at the joint center of
rotation is the product of muscle
force (Fm) and muscle moment
arm (d ).
6-32
Muscular Strength, Power and Endurance
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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-33
Muscular Strength, Power and Endurance
What is muscular 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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-34
Muscular Strength, Power and Endurance
The general shapes of the force-velocity and power-velocity curves for skeletal muscle.
For
ce
Velocity
Pow
er
Power-VelocityForce-Velocity
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-35
Muscular Strength, Power and Endurance
What is muscular endurance?
• the ability of muscle to exert tension over a period of time
• the opposite of muscle fatigability
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-36
Muscular Strength, Power and Endurance
What is the effect of muscle temperature on (warm up) ?
(the speeds of nerve and muscle functions increase)
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.
6-37
Muscular Strength, Power and Endurance
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
Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.