Week 4 - Skeletal Muscles & Exercise Flashcards
What is the resting energy expenditure per day of skeletal muscle?
54.5kJ/kg (13cal/kg)
What is the resting energy expenditure per day of adipose tissue?
18.8kJ/kg (4.5cal/kg)
What is the resting energy expenditure per day of bone?
9.6kJ/kg (2.3cal/kg)
What is the density of skeletal muscle?
1.06kg/L
Approximately 15% denser than fat
What is the density of adipose tissue?
0.92kg/L
What is the water:protein:salts/minerals % of skeletal muscle?
- Water: 75%
- Protein: 20%
- Salts/minerals: 5%
What percentage of body weight is skeletal muscle in healthy males and females?
- Males: 42%
- Females: 36%
What is the general organisation of skeletal muscle?
- Highly organised compartmentalised tissue
- Muscle fibres embedded in collagen matrixes, forming tendons or aponeurosis (at ends of muscles)
What are the levels or organisation in skeletal muscle? (5)
- Muscle
- Fascicle
- Muscle fibre
- Myofibrils
- Sacromeres
What are the roles of skeletal muscle? (4)
- Force
- Movement and posture
- Metabolism and thermoregulation
- Endocrine organ
What nervous system innervates skeletal muscle? How does it recruit muscle fibre?
- Somatic motor nervous system
- It recruits muscle fibres by recruiting motor units, all muscle fibres in a motor unit are the same
What are the 3 categories of motor unit?
- S: slow twitch, low tension, fatigue resistance (~type I fibres)
- FFR: fast fatigue resistance, fast twitch, moderate force (~type IIA fibres)
- FF: fast fatiguable, fast twitch, high force (~type IIX/IIB fibres)
What factors affect which motor units are best suited and recruited for a task? (4)
- Force required
- Duration of activity
- Availability of energy
- Fatigue of fibres
What is the size principle, in regards to progressive increase in force and motor unit recruitment?
The type and number of motor units recruited varies as increase in force requirements (exercise intensity)
S motor units have lower thresholds for activation, so are recruited first for light-moderate intensity activities
What are characteristics of slow motor units with type I fibres? (4)
- Usually small motor units
- Low-moderate force
- Long duration
- Many every day activities
What are characteristics of fast motor units with type IIA fibres? (4)
- Medium sized motor units
- Higher force
- Higher speed
- Moderate-long duration
What are characteristics of fast motor units with type IIX/IIB fibres? (4)
- Large to very large motor units
- High force
- High speed
- Short duration
What are 3 ways muscle fibres can be classified?
- Morphology (red/white, large/small, capillary density)
- Contractility (speed (twitch), force (tension), fatiguability)
- Metabolism (oxidative/glycolytic, myosin ATPase)
What are the two main muscle fibre categories? Which is dominant for aerobic and anaerobic activities? What else differs these two groups?
- Type I: dominant in aerobic (endurance) activities
- Type II: dominant in anaerobic (power) activities
Also differ by type of neuron innervation
For each major muscle fibre type (4), what are their speed usage and metabolic characteristics?
- Type I: slow, oxidative
- Type IIA: moderately fast, oxidative glycolytic
- Type IIX: fast, moderately oxidative glycolytic
- Type IIB: fast, glycolytic
What muscle fibre type do most people have in major arm and leg muscles?
45-55% of people have type I
What muscle fibre type would an endurance and power athlete predominantly have?
- More and larger type I for endurance athlete
- More and larger type II for power athlete
What are the neurological determinants of muscle force? (3)
- Number of motor units recruited: more MUs = more force, small motor units for fine motor control, large motor units for gross motors
- Size (type) of motor units recruited = larger MUs = more force
- Synchronicity of activation: Synchronus recruitment of motor units produces maximal forces in highly trained (eg. weightlifter)
Asynchronous recruitment of S/FFR motor units allows cycling of motor units for good fatigue resistance (eg. continuous training)
What are the anatomical-physiological determinants of muscle force? (8)
- Size of fibres (more myofibrils = more force)
- Cross-sectional area (larger muscle = larger cross-section = larger force)
- Muscle architecture/fibre alignment; parallel, pennated, other
- Muscle length: ratio of fibre to muscle length 0.2-0.6 (20-60% muscle length), shorter fibres usually stronger, longer fibres can shorten faster being more powerful but not as strong
- Sacromere length: extent of actin-myosin cross-bridge overlap and attachments influence muscle force
- Joint ROM: max muscle force varied through ROM, depending on its capacity and fibre length and sacromere overlap
- Velocity: as velocity increases, force decreases
- Fibre type: type II fibres produce more force and power than type I at the same velocity. Type II fibres can produce much more force and power at higher velocities
How are arrangement of muscle fibres described?
- Relative to the axis of force
What is parallel muscle architecture?
- Fibres parallel to force-generating axis
- Strap, fusiform, fan-shaped
- Example: biceps brachii
What is pennated muscle architecture?
- Fibres at an angle relative to force-generating axis, usually varying between 0-30°
- Unipennate: single angle
- Bipennate/multipennate: 2+ angles
- Example: deltoid
