Lecture 12 - Recruitment of Muscle Flashcards
What is the primary tissue activated during exercise?
Skeletal muscle
What is the resting energy expendature of skeletal muscle
Skeletal Muscle: 54.4 kJ/kg (13.0 kcal/kg) per day
How much does skeletal muscle constitute a average adults body weight?
Constitutes around 42% of a healthy male’s body weight and 36% of a healthy female’s body weight.
What are the roles of skeletal muscle?
• Force
• Movement and posture
• Metabolism and thermoregulation
• Possible Endocrine Organ
What part of the NS is responsible for activation of skeletal muscle
Somatic - SNS (voluntary)
What are the 3 types of motor units and which muscle fibres do these motor units innervate?
• S - slow twitch; low tension; fatigue resistant (~Type I fibres)
• FFR - fast twitch; moderate force; fatigue resistant (~Type IIA fibres)
• FF - fast twitch; high force; highly fatiguable (~Type IIX/IIB fibres)
Why are muscle fibres and motor units varied?
Recruitment patterns adapt based on the task at hand, considering the required force, activity duration, energy availability, and fiber fatigue.
What is the size principle
- The type and number of motor units recruited vary with increasing force requirements, affecting exercise intensity.
- S motor units, with lower activation thresholds, are recruited first for activities of light to moderate intensity.
Describe the a) main activities, b) force required and c) contraction time for Type I muscle fibres
Aerobic (endurance)
Low to moderate
Slow
Describe the a) main activities, b) force required and c) contraction time for Type IIA muscle fibres
Anaerobic & Aerobic (power & moderate endurance)
Higher
Fast
Describe the a) main activities, b) force required and c) contraction time for Type IIX muscle fibres
Anaerobic (power)
High
Very fast
Describe the a) main activities, b) force required and c) contraction time for Type IIB muscle fibres
Anaerobic (power)
High
Extremely fast
Describe the a) main fuel stores, b) fatigue resistance and c) size of motor neurons for Type I muscle fibres
a) fats, b) high, c) small
Describe the a) main fuel stores, b) fatigue resistance and c) size of motor neurons for Type IIA muscle fibres
a) carbs and fats, b) moderate, c) medium
Describe the a) main fuel stores, b) fatigue resistance and c) size of motor neurons for Type IIX muscle fibres
a) ATP & carbs, b) low, c) large
Describe the a) main fuel stores, b) fatigue resistance and c) size of motor neurons Type IIB muscle fibres
a) ATP & carbs, b) very low, c) very large
What does the colour of muscle fibres represent?
The color of muscle fibers (red vs. pale) is due to myoglobin content, which is tied to their oxidative capacity and role in oxygen storage.
What type of muscle do most people have in legs and arms?
45-55% Type I in major arm and leg muscles
When considering an endurance athlete and a power athlete, who would have type I and who would have type II fibres
E - Type I, P - Type II
What is the relationship between motor unit to muscle fibre ratio and function?
- Small motor units used for fine motor control (e.g., eye ~ 10 fibres/motor unit, finger ~ 300 fibres/motor unit)
- Large motor units used for gross locomotor movements (e.g., gastrocnemius ~ 2000 fibres/motor unit)
What is the relationship between power and velocity of movement
power increases and velocity increases
What is the relationship between force and speed of movement
force decreases and speed increases
Which fibre type produces more force and power and higher velocities?
Type II - much more
what is synchronous and asynchronous recruitment?
- Synchronous Recruitment: Utilized by highly trained individuals like weight-lifters to produce maximal forces.
- Asynchronous Recruitment: Employed in activities requiring good fatigue resistance, such as continuous running, by cycling S/FFR motor units.
What are the determinants of muscle force?
– Size of fibres
– Cross sectional area
– Muscle architecture
– Muscle length
– Sarcomere length
– Joint range of motion
– Velocity
– Fibre type
What are the classifications of muscles based on the arrangement of fibres?
Parallel – fibres parallel to force-generating axis, Pennated- fibres at an angle relative to force-generating axis
What is a complex muscle?
Muscle fibres do NOT run full length of the
muscle
What are the effects of muscle pennation on force?
– Pennation decreases each fibre’s maximum force on the
tendon
– However, pennation increases fibre packing and sarcomere
number per physiological cross-sectional area (PCSA) of
muscles
– Net increase PCSA results in greater force
What is the difference between teh length of fibres on producing force?
• Shorter fibres are usually stronger (force at a shorter length)
• Longer fibres can shorten faster (higher peak velocity)
With regards to the quads and hamstrings, which is specialised for force and which for speed? Why?
• Quadriceps – specialised for force, pennated, shorter fibre length
• Hamstrings – specialised for speed, non-pennated, longer fibre length
What is the relationship between muscle length and muscle force? Why is this the case?
Actin-myosin cross bridging developes force. Cross-bridge overlap influences the force generating ability of the muscle. Overlap is generally smallest at extremes of ROM and largest at the mid-point of ROM. This means that the muscles ability to generate force is typically larger mid-way through joints ROM.
What does muscle architecture determine about a muscles ability to produce force at slower speeds?
Muscles with shorter fibres and largers PSCAs can produce more force at slower speeds
