Lecture 2: Muscle physiology & adaptations Flashcards
epi
on
peri
around
endo
in
Connective tissue
connects all components of the body
- why muscle does not rip off the bone
- continuous with each other around fibres, bundles, and belly
Largest to Lowest
- Epimysium- continues with tendon
- Fasciculus- bundle of muscle fibres
- Perimysium-around each bundle of fibres
- Single muscle fiber-muscle cell
- Endomysium-around each fibre
- Myofibril- smallest unit
Motor unit
motor neuron and all its associated fibres
Nueromuscular Junction
junction between nerve cells and fibres
All or None Principle
- either reaches threshold and fires or it doesn’t
- if stimulus reaches threshold then we get complete contraction
- can stimulate a few or large number of muscle fibres
Myofibrils
Actin and Myosin
- arranged parallel with muscle fibres
- what gives muscle its striated appearance
Sarcomeres
functional unit of contraction
Cross-bridges
hook up to actin filament (like a hand over hand action pulling a rope)
myosin
thicker and darker
actin
thinner and lighter
Muscle Contraction
-when a motor neuron stimulates muscle fibres they will contract due to the sliding filament theory
Sliding filament theory
-cross bridges on the myosin attach to the actin and pull the thin filaments closer together, resulting in a shortening of the sarcomere (Z-lines more closer together)
H-zone
thick filaments only, myosin only
I-band
actin, light filaments
more cross-bridges=
stronger contraction
Stretched muscle
draw diagram
- has I-band, A-band, and H-zone
- z-line is not touching A-band
Completely Contracted Muscle
- NO I-band or H-zone
- z-line tight with a-band
Resting Muscle
- small I-band
- small H-zone
- z-line not touching but close to A-band
What is necessary for myosin crossbridge cycling with actin filaments
- Calcium and ATP
- Ca binds with protein on actin causing the protein to move out of the way exposing the binding site to the myosin globular head
What dictates the force of contraction
-number of cross-bridges that are attached to actin filaments at any instant in time
Type II Fibres
- fast-twitch
- higher force productions
Type I
-contraction sustained longer, force production slow, fatigue resistant, limited force production
Type IIx
- ability to change to type IIa through training
- high power capabilities
Type IIa
- more fatigue resistant than IIx
- less power capabilities
Size principle
lower threshold units are recruited first
-type I=lower threshold=recruited first
type II=higher threshold=high force=recruited later
Exception to Size principle
with heavy resistance training all muscle fibres get bigger because they are all recruited in consecutive order by their size to produce high levels of force,
- in advanced lifters the CNS might adapt by allowing these athletes to recruit some motor units not in consecutive order
- Selective Recruitment
- ability to recruit type II fibers & inhibit lower threshold units
- adaption
Sports with low Type I
100m sprint
Olympic weight-lifting
Football wide receiver
Basketball
Sports with high type 1
800m run* marathon barbell squat* soccer* field hockey* football lineman* distance cycling *=high in both
How can the force output of a muscle be changed?
- changing number of motor units activated
- changing frequency of activation of individual motor units
Parallel (Fusiform) Muscle
more length
wide ROM
ex) bicep
Convergent muscle
more power
wide surface area
pennate muscle
give more power due to wide surface area
-bi, uni, multi (based on # of tendons)
Sphincter
open and close
Power
from surface area
ROM
from length
Isometric
muscle contraction that does not produce movement
Isotonic
contraction that does produce movement
eccentric or concentric
Concentric
fibers and attachments move closer together causing joint movement
Eccentric
muscle fibers lengthen
- strongest
- gravity helps out
- more cross bridge alignment, keeping cross bridges on the actin=no reattaching, just continuous
Proprioceptors
-specialized sensory receptors that provideCNS with info needed to maintain muscle tone and perform complex coordinated movements
Muscle spindle
protects
- modified muscle fibres that provide info concerning muscle length and rate of change in length, help control activation of the muscle
- detects shortening and helps increase contraction
GTO
- relaxes the muscle
- located in tendon
- attached end to end with extrafusal fibres
- work to protect excessive tension by inhibiting muscle activation
- senses tension it sends signal to relax muscle
- inhibits contraction
Phosphagen system
ATP-PCr
- provides immediate ATP energy
- fast powerful movements
- short-duration, high intensity
- long rest periods
- peak= 1st few seconds
- capacity= 20 to 30s
Glycolytic system
breaks down glucose to lactic acid
- next readily available source of ATP
- longer, less intense exercise
- shorter rest periods
- peak=20-30s
- capacity=2-3min
Aerobic System
oxidative
- role in ,maintaing power output and recovering energy stores
- lower intensity
- long duration
ex) running, walking, skiing
Aerobic endurance training
-does not enhance muscle strength or size
-may compromise benefits of resistance training
why?-competing adaptations
-can start breaking down protein in muscle
when may aerobic training help increase strength?
- unfit sedentary people
- circuit training
- cross-fit
Does resistance training impact VO2 max?
no- not on aerobic power either
Major Adaptations to Resistance vs. Aerobic Training
See table 5.2 and 6.1
Overtraining
excessive frequency, volume, or intensity of training resulting in fatigue, illness, or injury
-can cause dramatic decrease in performance of all training levels
Stages of Training
acute stimulus-> overload -> acute fatigue -> overreaching (planned) -> chronic fatigue -> overtraining
Markers of Overtraining
- acute epinephrine and norepinephrine increases beyond normal exercise-induced levels
- psychological effects- low desire to train, low joy from training
- altered resting HR, ^submax HR, ^muscle soreness, ^injury, altered cortisol concentration, lower VO2 max, altered BP, low muscle glycogen
POMS
profile of mood states
- good profile vs. bad profile
- inverted profile can be an indication of overtraining/burnout (iceberg profile)
Detraining
- cessation of anaerobic training or large reduction in frequency, volume, intesnity or combination of variables
- can cause decrements in performance and loss of physiological adaptations
- can occur in 2 weeks with resistance+aerobic training
- can regain quicker if previously fit
Physiological Responses to Training and Detraining
-a detrained person is likely to be better at aerobic activities than resistance
FIG- 5.6
Neural Adaptations
- motor unit recruitment, firing rate, GTO inhibition take place first before increase in physical size
- will be able to lift more due to this
MES
minimal essential strain
- bone cells stimulated and migrate to area of stress to make bone thicker
- when forces that reach or exceed a threshold stimulus initiate new bone formation in the area experiencing mechanical strain
Stimulating bone formation
- use exercises that directly load particular regions- specificity of loading
- use structural exercises involving multiple joints ex) squat, dead lift, power clean
- Prgressively overload the musculoskeletal system and increase load
- vary exercise selection
Hypertrophy
- increase in synthesis of contractile proteins
- increase in number of myofibrils
- increase in diameter
Hyperplasia
- theory that preexisting muscle fibres splits or satellite cells, ^# of muscle fibres
- does not exist in humans
Strength Adaptations
high load, few repetitions, full recovery period
Muscle Size
moderate load
high volume
short to moderate rest periods
8-12 reps, building some muscle, more toning
Muscular Endurance
low intenisty
high volume
little recovery
-12-15-20 reps
Connective tissue adaptations
increased collagen metabolism
-must adapt and grow and respond with hypertrophy
Collagen
building block of all types of connective tissue
If connective tissue doesn’t grow at same rate…
compartment syndrome puts pain on muscle
Specific changes within a tendon that increase in its cross-sectional and strength in response to functional overload include…
- increase in collagen fibril diameter
- ^# of covalent cross-links within a fibre of increased diameter (ability to stick together)
- ^ in # of collagen fibres
- ^ in packing density of collagen fibres
- lead to stronger connective tissue
Stimulating Connective Tissue adaptations
- exercise of low to moderate intensity does not change collagen content of connective tissue
- high intensity loading results in a net growth of involved connective tissue
- the better the ROM the more efficient the diffusion throughout the ROM of the join
Cartilage as a connective tissue is…
avascular (does not get its own blood supply)
- meniscus injuries do not heal on their own
- must get diffusion from surrounding tissues
