Muscle heterogeneity and performance Flashcards
What are the requirements of skeletal muscle?
1) Strength & speed –> explosive power e.g. weightlifting, sprinting
2) Fatigue resistance (endurance) –> power maintenance e.g. marathon (don’t need high force or high power generated contractions; want something to sustain activity.
A mixture exists in everyday life.
What are force and speed determined by?
Force - determined by size
Speed - determined by type of molecular motor
What is power?
Product of force x velocity
What is the difference between marathon runners and sprinters?
Marathon runners:
- low muscle mass
- fast muscle composition
- high-power output (instantaneous)
- low fatigue-resistance
Sprinters:
- large muscle mass
- slow muscle composition
- low power output (maintained over a prolonged period of time)
- high fatigue-resistance
(adapted cardiovascular & respiratory systems - allow muscle metabolism to continue through aerobic processes)
What are slow and fast fibres?
Slow (type I) = red/high myoglobin* content - dark pigment
Fast (type II) = white/low myoglobin content - light pigment
- Majority = standing around so STF
- Protein = O2 binding (like haemoglobin)
What are FTF for?
- high power generation
- short bursts of power
What determines the speed of a twitch?
1) Activation
- rate of calcium release from SR
2) Cross-bridge kinetics
- myosin ATPase/ myosin isoform composition
= how quickly molecular motors + CB come to a 2nd turnover
What is the EMD?
Electrode mechanical delay.
Everything going on inside a muscle before a force is generated.
What can be controlled in a muscle?
- Can control motor units
- Cannot control muscle fibres
What is a tetanus?
Mechanical response to multiple electrical stimuli, in slow and fast muscles.
How does a muscle twitch occur?
By electrically stimulating the muscle
Whatis the frequency response relationship?
- orderly recruitment
- STF recruited first bc of shorter axons
- energy saving
What are unfused signals?
- have more time to relax
- behave differently to same signal
- series of twitches
What are fused signals?
- produce a smooth contraction
What determines the speed of a twitch?
1) activation: rate of ca2+ release from SR
2) CB kinetics: myosin ATPase/myosin isoform composition
- can’t send AP down CNS to activate a whole muscle
- need to stimulate a muscle to twitch it
What are motor units classified into?
1) slow-fatigue resistance (SR)
2) fast-fatigue resistance (FFR)
3) fast-fatiguable resistance (FF)
- repeatedly stimulate muscle
- force declined over time
- moderate decline in slow fibres but more substantial in faster fibres
What were the characteristics of slow muscle fibres?
1) twitch properties = ST
2) twitch & fatigue = ST
3) colour (myoglobin) = red
4) twitch & metabolism = SO
What were the characteristics of fast muscle fibres?
1) twitch properties = FT(a)
2) twitch & fatigue = FFR
3) colour (myoglobin) = white
4) twitch & metabolism = FO
What were the characteristics of the fastest muscle fibres?
1) twitch properties = FT(b)
2) twitch & fatigue = FF
3) colour (myoglobin) = white
4) twitch & metabolism = FG
What reaction determines the fibre type of muscles?
- CB cycling
- myosin attaches to actin
- ATP hydrolysed to ADP + Pi
How are fibres classified based on speed of contraction, substrate and enzyme characteristics?
Slow twitch:
- high oxidative enzyme activity
- low glycolytic enzyme activity
Fast-twitch oxidative:
- medium oxidative enzyme activity
- medium glycolytic enzyme activity
Fast-twitch glycolytic:
- low oxidative enzyme activity
- high glycolytic enzyme activity
Ox = HAD, SDH, CS (aerobic) Gly = LDH, PFK, PHOS (anaerobic)
How are fibre types classified?
1) fast and slow twitch fibres
2) type I and type II fibres
3) myosin heavy chain isoforms
