L288 Exercise Physiology - Muscles, Fuels and Fatigue Flashcards
What kind of muscle fibre is correlated with lower body fat % and why?
• ↑ % Type I fibres, ↓ body fat % - because type I fibres have greater oxidative capacity than type II
Human muscle fibre types: how do they stain with different pH solutions?
• Type 1 fibres stain dark after acidic, and type II dark after alkaline, pre-incubation
List the different muscle fibre types
- Type I (slow-twitch)
2. Type II (fast-twitch): IIa and IIx
Characteristics of type I fibres
- oxidative , high mitochondrial density
- MHCI, well vascularised
- Low and slow force generation, fatigue-resistant
Type IIa vs IIx fibre characteristics
IIa:
- MHCII
- medium vascularity, mit density, vascularity, force gen and time to force gen
- fatigue-resistant
IIx:
- MHCII
- low vascularity, mit density, vascularity, force gen and time to force gen
- fatigue susceptible
Type IIx fibres: in whom are they usually found and why?
Sprinters - hard to train muscles to increase IIx fibres - pretty much born with it
Muscle fibre type: order of recruitment
I fibres first, then IIa, then IIx last
Fibre type recruitment depends on which two factors?
A. Intensity
B. Duration (of exercise)
Muscle fibre phenotype: what is it dependent on?
A. genetics
B. training: to fully express the phenotype you’re born with, you need to train!
What are the increases in strength with resistance training due to?
- most of early increases in strength due to NM adaptations
- Over time, increases in strength mostly due to muscle changes
- However there are muscle architectural changes early on
What happens to muscle mass with disuse?
- Muscle mass decreases very quickly
Molecular regulation of muscle mass: examples of signals that play a role in hypertrophy and atrophy
- mTOR for hypertrophy
- atrogenes e.g. foxo for atrophy
Primary adaptations to endurance exercise lie in which part of the muscle, and why?
Mitochondria - being better able to utilise and store energy is beneficial
Mitochondrial adaptations to exercise training (5)
- ↑ mitochondrial density and oxidative enzymes
- ↓ CHO use and lactate production
- ↑ fat oxidation
- ↑ endurance performance
- ↑ insulin action
Exercise and skeletal muscle GLUT4 expression: relationship
↑ exercise, ↑ skeletal muscle GLUT4 exp
Human muscle: homo or heterogenous cw animal muscle
Homogenous cw animal muscle
Why do we need pathways to generate ATP?
We cannot store large amounts of ATP in muscle
Outline 4 major fuel pathways for generating ATP in muscle
- Creatine phosphate
- Glycolysis - substrate level phosphorylation
- CHO ox phos
- FFA ox phos
What is importantly produced through glycolysis, and why is it important?
Lactic acid - helps regenerate NAD to maintain glycolysis
ATP yield vs. capacity of the different major fuel pathways for muscle
• Glycolysis and PCr (substrate level phos)
- Produce ATP quickly but with low capacity
• CHO and FFA ox
- Produce ATP slowly but with high capacity
ATP capacity and speed of oxidation of CHO vs FFA oxidation
- CHO > FFA speed of oxidation
- FFA > CHO ATP capacity
Major fuels for sprinting
• Anaerobic fuels (PCr, glycolysis) mostly for short duration, high-intensity efforts
What happens with increased sprint duration with regards to fuel reliance?
• With ↑ sprint duration, ↓PCr reliance and ↑ glycolysis reliance
Major fuels with increased exercise intensity
- ↑ intensity → ↑CHO (esp. muscle glycogen) and fat reliance
- Optimal fat loss only at 60-65% of VO2max
