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Chapter 3

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by

John Gibson

on 3 October 2016

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Transcript of Chapter 3

Skeletal Muscle System
Muscle Cell
Contractile Proteins
Connective Tissue
Helps prevent the muscle activation signal from spreading to adjacent muscle fibers
Stretch-Shortening Cycle
Controlled muscle elongation (Eccentric)
Rapid muscle shortening (Concentric)
Finger on chest example
One component of the elasticity comes from the connective tissue covering the muscles
epimysium
perimysium
endomysium
Training for force and power production
Sarcomere
contractile unit of skeletal muscle
skeletal muscle = striated muscle
http://www.wellcome.ac.uk/Education-resources/Education-and-learning/Big-Picture/All-issues/Exercise-energy-and-movement/WTDV033020.htm
Noncontractile Proteins
Provides the structure of the contractile proteins
Also contribute to the elastic component of the muscle tissue
Titin = Connects Z line to M line, stabilizes myosin
Nebulin = Starts at Z line, runs the length of actin
Actin Filament
Two helices of actin molecules
attached to Z line
Active site = place where myosin attach
Tropomyosin
Troponin
Tropomyosin
Wraps around the actin filament covering the active sites
Must be pulled away for a contraction to occur
Troponin
Troponin I = Binds actin
Troponin T = Binds Tropomyosin
Troponin C = Binds Calcium
Calcium causes troponin to pull tropomyosin off the actin active sites
Myosin Filament
Globular head
hinged pivot point
fibrous tail
Crossbridge
Crossbridge
Two myosin molecules
Made from myosin ATPase
Different isoforms
determines fiber type
contractile characteristics of fiber
Muscle Fiber Types
Several different classifications
histochemical
biochemical
physical
Fiber types are determined at birth
They can be changed a little
Fiber Type Change
Types of activity (strongest stimulus for change)
hormonal concentrations
aging - mostly losing type II
Muscle Biopsy
Make an incision into the muscle
suck some tissue into the biopsy needle
clip a portion of the muscle off
put muscle tissue into liquid nitrogen
cut a small slice of tissue in a cryo cut
Histochemical Myosin ATPase Staining
classification based on histochemica reactions of ATPase with ATP supplied in staining process
isoforms catalyze reactions at different rates, resulting in different staining intensities
Type I
Type II
Subtypes
Classifications
Red and White fibers
Fast-Twitch and Slow Twitch
Slow Oxidative, Fast Oxidative Glycolytic, Fast Glycolytic
Type I and Type II
Type I
Slow Twitch
Reaches peak force production at a slow rate
Oxidative metabolism
rich blood supply
high mitochodrial density
fatigue resistant
contract over long periods of time with little change in force production
Well suited for endurance
Type II
Fast twitch fibers
develop force rapidly
high force production capabilities
not a lot of mitochondria
fatigue easily
Subtypes
From most oxidative to most glycolytic
Type I
Type IC
Type IIC
Type IIAC
Type IIA
Type IIAX
Type IIX
Myosin Heavy Chains
Myosin filament is made up of two heavy chains and two pairs of light chains
Some like to fiber type by MHC
Electrophoresis
3 Different Types
Strong correlation with histochemical
Dissolve tissue into a solution
Pull solution through a gel
Different sized pores
larger proteins stop at the top
smaller proteins make it to the bottom
Fiber Types
I
IIa
IIx
In animals IIb
Correlation
histochemicals main fiber types
I, IIA, IIX
MHC
I, IIa, IIx
Very strong correlation between the characteristics of these muscles fibers
Sliding Filament Theory
The number of interactions between myosin and actin dictates the force of the contraction
Start of A Contraction
Propagation of Electrical Impulse
Impulse spreads across cell membrane
travels down transverse (T) tubules
activates Dihydropyridine receptors
activates ryanodine receptors/channels
Calcium is released
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html
Power Stroke
Start from bound Myosin
ATP must bind to release myosin
ATP hydrolyzes to produce energy to "cock" mysoin back into place
Myosin weakly binds to actin
Pi leaves causing a tighter bond
ADP releases causing tighter bond and pull of myosin on actin
calcium is taken back into the SR to allow the muscle to relax
Returning To Resting Length
Myosin and actin interaction can only pull Z-lines together
To return to resting length an outside force must pull the muscle
gravity
antagonistic muscle
Proprioception and Kinesthetic Sense
Ability to sense motion and position
proprioceptors are receptors found in the muscles and tendons
Motor Learning
Muscle Spindles
Golgi Tendon Organs
Motor Learning
ability to repeat a specific motor unit recruitment pattern resulting in a successful performance of a skill
Muscle Spindles
Proprioceptors in skeletal muscles
monitor stretch or length of muscle
initiate contraction when stretched
makes contractions more powerful
may limit flexibility
located in intrafusal fibers
Nervous System
Intrafusal Fibers
fibers within the spindle fiber
stretch sensitive central area
sensory nerve carries impulse to the spinal cord
transfers impulse to alpha motor neurons
relay impulse to extrafusal fibers causing contraction
Neurons
alpha motor neurons innervate muscle fibers that do not contain spindle fibers
gamma motor neurons innervate intrafusal fibers
spindle fibers can be lengthened and shortened to help control the muscle
Golgi Tendon Organs
Found in the tendons
When tension gets too high it inhibits muscle activation
sensory neurons from the golgi synapse with alpha motor neurons inhibiting their action
Whole body vibration
Whole Body Vibration
Increases spindle activity
Decreases Golgi activity
A lot of research showing benefits
increased strength
increased testosterone
faster recovery
improved flexibility
etc.
Types of Muscle Actions
Concentric - Shortening
Eccentric - Lengthening
load or resistance is greater than the force produced by the muscle
Isometric - Same Length
the myosin heads keep attaching and detaching at the same or close to the same active site on the actin filament
Resistance Exercise Descriptive Terms
Isotonic - same constant tension
can't happen in muscle without advanced technology
Dynamic Constant External Resistance
Resistance stays the same throughout the movement
Isointernal
variable velocity and constant resistance
Variable resistance
change in resistance over the range of motion
Isokinetic
Isokinetic
Constant velocity throughout movement
Used to measure torque at a specific velocity
Physical Therapist
test joint function
Can only be done on one joint
Doesn't translate to real life movement
Force-Velocity Curve
Concentric
Force drops as velocity increases
Eccentric
Force increases as velocity increases
Progressive Overload
Gradually increasing the resistance or load during exercise sessions
We can also progressively overload by adjusting the volume
Limit DOMS in untrained individuals
Power
Force x Velocity
Training heavy and slow only increases force at slower velocities
Training light and fast only increases force at higher velocities
Strength Curves
Ascending
Strength increases as muscle shortens
e.g. Squat
Descending
Strength decrease as muscle shortens
e.g. Upright row (what muscles are working)
Bell
e.g. Bicep curl
Different exercises/joints/muscles begin and end and different levels of overlap between myosin and actin
Effects of Endurance Training
SAID - Specific Adaptation to Imposed Demand
Only the fibers that are recruited will adapt to the exercise
Type I fibers are recruited first in all exercises
As intensity increases then Type II will be recruited
Endurance training actually decreases the size of Type I fibers
Helps with oxygen transportation
Hypertrophy
Addition of myofibrils to existing fibers, increases muscle size
Type II fibers grow more than Type I
Type II response to resistance training
increase in the rate of protein synthesis
Type I response to resistance training
decrease in the rate of protein degradation
Nuclear Domain
Nuclear Domain
To support an increase in the size of a muscle fiber we need more myonuclei
satellite cells are found between cell membranes
damage to the muscle cell exposes the satellite cells
They then become fused into the muscle fiber
Hyperplasia
Growth of new muscle cells
Debatable idea
Bodybuilders have same size muscle cells, but larger muscles
Power lifters have more fibers showing new formation
Steroid seem to enhance this growth
Compatibility of Exercise Training
Endurance training reduces strength at high velocities (power)
Anaerobic performance may be negatively affected by endurance training
VO2 max is not compromised by heavy resistance training
Time to exhaustion at any given intensity is not negatively affected by strength training
Fiber type changes
Fiber Type Changes
Endurance Only
Type I - atrophy
Type II - no change
Strength only
All fiber types get larger
Combined
Type I - No change
Type II - get larger
Periodization and Prioritization
Periodization - varying the volume and intensity of the training
Prioritization - prioritizing what goals will be focused on in a training program
Full transcript