Copyright © 2012 American College of Sports Medicine Chapter 4 Muscular Adaptations to Training.
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Transcript of Copyright © 2012 American College of Sports Medicine Chapter 4 Muscular Adaptations to Training.
Copyright © 2012 American College of Sports Medicine
Muscle TypesMuscle Types
• Cardiac– Heart walls
– Contracts involuntarily with strong force
– Responsible for creating rhythmic pressure & moving blood
• Smooth– Walls of hollow organs & blood vessels
– Contracts involuntarily, causing constriction
• Skeletal– 40% of body mass
– Contracts voluntarily, rapidly
Copyright © 2012 American College of Sports Medicine
Roles of Skeletal MusclesRoles of Skeletal Muscles
• Functions– Produce tension
– Act on bones to produce movement
– Produce body heat
– Maintain posture
– Assist with communication—aids in ventilation
• Attachments– Proximal (origin): closest to midline
– Distal (insertion): farthest from midline
• Movement at Joints– Uniarticular: produce movement at one joint
– Multiarticular: produce movement at two joints
Copyright © 2012 American College of Sports Medicine
Roles of Skeletal Muscles (cont’d)Roles of Skeletal Muscles (cont’d)
• Agonist– A muscle that contracts to perform a specific movement
• Antagonist– A muscle that opposes agonist movement
• Stabilizer or Fixator– A muscle that contracts to stabilize point of origin or insertion for a
corresponding muscle
• Neutralizer– A muscle that contracts to eliminate one movement of a
multiarticular muscle
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Gross AnatomySkeletal Muscle Gross Anatomy
• Skeletal Muscle Is Designed to:
– Generate high levels of force efficiently
– Transmit forces effectively to bone
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Gross Anatomy (cont’d)Skeletal Muscle Gross Anatomy (cont’d)
• Myofilament– Basic structural unit of skeletal muscle
– Composed of contractile proteins actin & myosin
• Sarcomere– Basic functional unit of muscle
– Composed of myofilaments
• Myofibril: bundle of sarcomeres
• Muscle Fiber: bundle of myofibrils
• Fascicle: bundle of muscle fibers
Copyright © 2012 American College of Sports Medicine
Schematic Drawing of a MuscleSchematic Drawing of a Muscle
• Figure 1.1 (next slide)
– Schematic drawing of a muscle illustrating three types of connective tissue:
• Epimysium (the outer layer)
• Perimysium (surrounding each fasciculus, or group of fibers)
• Endomysium (surrounding individual fibers)
Copyright © 2012 American College of Sports Medicine
Muscle Fiber OrganizationMuscle Fiber Organization
• Sarcolemma: cell membrane surrounding muscle fiber
• T tubules: propagate action potential into muscle fiber
• Sarcoplasm– Liquid cytoplasm surrounding myofibrils
– Contains enzymes, fat, glycogen, mitochondrion, nuclei
• Sarcoplasmic reticulum: lattice of conductile tissue
• Terminal cisternae: lateral sacs that store calcium
• Nucleus: contains genetic material, involved in protein synthesis—The muscle fiber has many peripherally located nuclei.
Copyright © 2012 American College of Sports Medicine
Muscle Fiber Organization (cont’d)Muscle Fiber Organization (cont’d)
Copyright © 2012 American College of Sports Medicine
Structure of a SarcomereStructure of a Sarcomere
Copyright © 2012 American College of Sports Medicine
The Myofibrillar ProteinsThe Myofibrillar Proteins
Copyright © 2012 American College of Sports Medicine
Muscle Fiber Organization (cont’d)Muscle Fiber Organization (cont’d)
• Muscle Contraction: The Sliding Filament Theory– Thick & thin filaments slide past each other w/o changing length
– Sarcomere shortens in series
– Muscle fibers & muscle belly shorten
– Results in movement & force generation
– Three stages
• Excitation-contraction coupling
• Cross-bridge cycling
• Relaxation
Copyright © 2012 American College of Sports Medicine
Muscle Fiber Organization (cont’d)Muscle Fiber Organization (cont’d)
• Skeletal Muscle’s Graded Responses
– Twitch: contraction of muscle in response to a stimulus
– Summation: effect of multiple twitches
• Spatial summation: activation of multiple motor units thereby contributing to force production
• Temporal summation: motor unit increases frequency of discharge to increase force
– Tetanus: maximal force production when summation is peaked
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and AdaptationsSkeletal Muscle Characteristics and Adaptations
• Muscle Fiber Formation: Myogenesis– Critical to normal muscle function
– Replacement of old/damaged muscle fibers in tissue remodeling
– Satellite cells (stem cells):
• Are released from basal lamina
• Migrate to area of fiber formation
• Proliferate
• Differentiate into myoblasts
– Myoblasts fuse to form myotubules, which mature into new fibers
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Muscle Fiber Types– Slow-Twitch (ST) or Type I: (red) endurance fibers
• Type I
• Type IC
– Fast-Twitch (FT) or Type II: (white) strength/power fibers
• Type IIC
• Type IIA
• Type IIAX
• Type IIX
Copyright © 2012 American College of Sports Medicine
Fiber-Type Continuum With Force and Endurance RatingsFiber-Type Continuum With Force and Endurance Ratings
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Fiber Types in Athletes– Ratio of fiber types in a muscle determines muscle’s functional
capacity
– Each muscle has distinct ratio & may favor one type or the other
– Endurance athletes: larger % of type I
• Long- & middle-distance runners
• Cyclists
– Strength/power athletes: larger % of type II
• Sprinters, throwers, weightlifters, jumpers
– Genetic predisposition
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Fiber-Types Transitions
– With RT, transitions take place from IIX to IIA
– Transition causes more force to be produced over time
– Detraining results in transition back to IIX
– No evidence yet of transitions between Types I & II
Copyright © 2012 American College of Sports Medicine
Fiber-Type Transitions With Training and DetrainingFiber-Type Transitions With Training and Detraining
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Muscle Hypertrophy
– Increase in muscle size
– Common adaptation to anaerobic training, especially RT
– Larger muscle = stronger muscle
– Results from:
• Increase in protein synthesis
• Decrease in protein breakdown
• Combination of two
Copyright © 2012 American College of Sports Medicine
Muscle Growth in the Quadriceps Muscle Following RTMuscle Growth in the Quadriceps Muscle Following RT
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Muscle Hypertrophy and Fiber Types– Hypertrophy occurs in both ST & FT muscle fibers
– Higher growth potential in FT fibers
• Factors Influencing Muscle Hypertrophy– Mechanical
– Circulatory
– Nutritional
• Muscle Hypertrophy and Other Training Modalities– Sprint & power training increase muscle size to lesser extent than
RT
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Hyperplasia
– Longitudinal splitting of existing muscle fibers
– Results in increased number of muscle cells
– May occur via increase satellite cell proliferation after muscle damage
– Shown in lab animals, but controversial in humans
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Structural Changes to Muscle– Structural changes can cause increases in:
• Strength
• Power
• Size
– RT increases:
• Endurance
• # of myofibrils
• Density of sarcoplasm, sarcoplasmic reticulum, & T tubules
• Sodium-potassium ATPase pump activity
Copyright © 2012 American College of Sports Medicine
Skeletal Muscle Characteristics and Adaptations (cont’d)Skeletal Muscle Characteristics and Adaptations (cont’d)
• Other Changes to Skeletal Muscle– Sprint & RT
• Increase anaerobic substrate content
• Increase muscle’s buffer capacity
• Alter enzyme activity
• Up-regulates anabolic hormone receptors (RT)
– Aerobic training
• Increases activity of aerobic enzymes
• Increases mitochondrial & capillary density (decreased by RT)