Muscle Structure and Function Flashcards
1
Q
Provide an overview of muscle structure
A
- Sarcomere, myofibril, muscle fibre, fascicle, muscle
- Sarcomere: Smallest contractile unit, contain protein filaments (A and M) , between 2 transverse Z discs and H zone in middle
- Myosin: Thick filaments with globular heads (attach to actin)
- Actin: Thin filaments, twisted helix, tropomyosin and troponin
- Postural (higher type I)
- Power muscles (higher type II)
2
Q
What are the mechanisms of muscle contraction at rest vs contracting
A
- Rest: No connection between A and M, high affinity, unable to bind due to tropomyosin (covering bind site on A) and troponin (holds tropomyosin in place)
- Ca: Facilitates removal of T and T
- ATP: M head binds ATP and produces ADP, leads to cross bridge and power stroke
3
Q
Describe the process of sliding filament model
A
- AP triggers voltage sensitive proteins / Ca channels in sarcoplasmic reticulum to open
- Ca floods into cell, troponin + Ca bind → movement of tropomyosin away from active sites
- M heads + ADP + P + energy → head extends = binds to A
- Releases stored energy and M changes shape → pull on strands and shrink sarcomere
- Generate force (power stroke)
- ADP + P unbind → new ATP binds in place on M head → release from A, breakdown ATP to ADP + P and repeat process on another A
- Cross bridges detach, Ca unbinds and M cannot bind to A anymore
4
Q
What is excitation contraction coupling
A
- Sequence of events that begin with a neural impulse and end with contraction, excitation of a motor nerve, propagation of an action potential
- Events at the neuromuscular junction, calcium release from sarcoplasmic reticulum
- Sliding filament theory and muscle contraction
- Power production is the key determinant of recruitment
5
Q
What are type I muscle fibres
A
- Slow twitch (slow contractile speed)
- Small in diameter
- Low force production
- High oxidative (aerobic) capacity
- Many mitochondria / capillaries / myoglobin
- High aerobic enzyme activity and highly resistant to fatigue
- Dominant muscle fibre during exercise below CP
- Linear relationship between number of slow twitch and VO2max
6
Q
What are type II muscle fibres
A
- Fast twitch (fast contractile speed)
- Large in diameter
- High force production and glycolytic capacity
- Many glycolytic enzymes, greater glycogen and PCr stores
- Highly fatiguable, recruited during high-intensity exercise
- A: Few mitochondria, highly fatiguable, anaerobic, low efficiency, exercise higher than CP
- X: Many mitochondria, slightly fatiguable, combination, moderate efficiency, short high intensity exercise (<1min)
7
Q
How do fibres respond to training
A
- Aerobic training, conversion of type II X to type II A to type I
- Distance runners 70-80% type I
- Track sprinters 25-30% type I
- Non-athletes 47-53% type I
8
Q
How are muscle fibre types assessed
A
- Muscle Biopsy
- Site is anaesthetised, small incision is made (1-3cm)
- Needle inserted into muscle
- 10-100mg sample is extracted (grain of rice)
- From metabolically active sites
- Sample stained to identify fibre type
9
Q
What is the purpose of training
A
- Improvements in health and performance
- Cardiorespiratory fitness
- Muscular strength and endurance
- Body composition, flexibility, speed, agility, power, adaptation
10
Q
What is overloading
A
- Principle of training
- Training load beyond level athlete is accustomed to
- Progressive overloading is required for continued improvement
- Adequate recover and sufficient stress prevent overtraining
11
Q
What is adaptation and reversibility
A
- Principle of training
- Training adaptation is not permanent, decay once stimulus is removed
- Improvement only possible if stimulus increases over time
- Same load = adaptation and then plateau
- Excessive stimulus = inability to adapt, decrease in performance
12
Q
What is the FITT principle
A
- Training loads can be monitored / modified, assessing
- Frequency (how often)
- Intensity (how hard, energy expenditure, RPE)
- Time (how long)
- Type (training method(s))
- Higher relative training intensity increases max VO2
13
Q
What are the principles of training / their purpose
A
- Specificity
- Overload
- Reversibility
- Applying these principles promotes improvement through adaptation
14
Q
What is specificity
A
- Principle of training
- Responses to training are specific to type of exercise, muscle groups and energy systems used
- SAID Principle: Adaptations are specific to stimulus
15
Q
What is karvonens HR reserve
A
- HRR = difference between resting and maximal HR
- HRR = HR max – HR rest
- Training HR (THR) should be 80-90% of HR max for endurance athletes