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Biomechanics of Skeletal Muscle
(Ch 6) Objectives
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Identify the basic behavioral properties of the
musculotendinous unit.
Explain the relationships of fiber types and
fiber architecture to muscle function.
Explain how skeletal muscles function to
produce coordinated movement of the human
body.
Discuss the effects of angle of pull, forcevelocity and length-tension relationships
Discuss the concepts of strength, power, and
endurance from a biomechanical perspective.
Properties, structure and function of
muscle
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Properties of muscle-tendon function
- Extensibility and elasticity
• Elastic and contractile components (Fig 6.2, p 147)
- Irritability and the ability to develop tension
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Structural Org of Skeletal Muscle (Fig 6.3 – 6.6)
Motor Unit (Fig 6.7, p 151)
Classification of Muscles
- by fiber architecture: parallel, pennate (F 6.11, p 155)
- by articulation (number of joints crossed)
• uniarticulate, biarticulate
• passive and active insufficiency
Biarticular muscle action and
synergy
Passive insufficiency – due to inability of a
multiarticular muscle to allow full ROM at
both ends
Active Insufficiency – due to inability of a
multiarticular muscle to generate force when
shortened at one end
Electromyography and fiber type
recruitment
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The motor unit and Electromyography (Figure from
lab)
- motoneuron & all innervated fibers
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Muscle Fiber Types
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Slow twitch oxidative (SO), or Type I
Fast twitch oxidative glycolitic (FOG), or Type IIA
Fast twitch glycolitic (FG), or IIB
Functional differences -Fig 6.10, p 152
Characteristics - Table 6.2, p 153
Selective recruitment of fiber types – size principle:
• SO
FOG
FG
Muscle Fiber
Types
Recruitment proceeds from smallest fibers to largest
(the size principle)
Factors Influencing Production of
Muscular Tension and Applied
Force
Force-velocity relationship - Fig 6.17, p 162
 Length - tension relationship - Fig 6.18, p 164
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- Elastic and contractile components
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Angle of pull - Max turning effect at 90 deg
Forcevelocity
relationship:
Active
insufficiency:
lengthtension
relationship:
Angle of Pull of Muscle &
degree of force application
Turning component equals
Force times sin θ
Mechanical Advantage of Elbow
Flexors
Length of Elbow Flexors as
Joint Angle Changes
Study Questions For Chapter 6
Biomechanics of Skeletal Muscle
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Self-study questions:
- What do these terms mean:
• Strength
• Endurance
• Power
- Intro probs, p 173, #1,3,8; Add probs, 174 p # 1,2
(My sketch of problem #2 is on next slide)
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Homework – due Monday, March 8
- Intro prob, p 173, #9; Add probs, p 174, # 8,9
Additional problem #2, p 173: Length-tension,
angle of pull combined
Sine of