Reflexes, recruitment, and control Flashcards
what is the formula for power
force x velocity
(uses instantaneous force and velocity)
- therefore it’s the mechanical power at an instant in time
at what velocity does the max power occur
30% of max shortening velocity
what does instantaneous power vary with
contraction velocity and fibre type
how does power change with fast fibres
fast fibres can reach faster contraction velocities
can produce more max power
only fibre type able to produce power at faster contraction velocities
how does power change with slow fibres
can only reach lower contraction velocities and therefore lower max power compared to fast fibres
have a region where they stop being able to produce force (and power) due to the contraction velocity
what is the difference in ATP consumption between fast and slow fibres
rate of ATP consumption = rate that it is consuming metabolic energy
- higher for fast fibres (they require more energy)
- positive slope for both fibres
— faster the contraction velocity, the higher the rate of consumption
what is the formula for efficiency
mechanical power / metabolic energy rate
- proportional to the ATP consumption
(what you mechanically got out fo something compared to the “cost” - metabolic energy consumed)
what is the difference in efficiency for fast and slow fibres
approx the same
however, fast fibres are the only ones able to produce force and power at higher speeds and therefore are the only ones efficient at that point
when is the efficiency of fibres zero
when they are unable to produce power
- lower in slow fibres
which fibres are recruited first
slow fibres recruited before fast fibres
(slow are smaller, fast are larger)
why are slow fibres recruited first
smaller MUs have smaller cell bodies adn larger SA to volume ratios
- more likely to experience a change in voltage large enough to reach threshold faster
what is the benefit of orderly recruitment
allows for smooth increases in force
simplifies control - one rule to control many levels of stimulations
what is differential / task dependent recruitment
sometimes fast fibres are recruited first (before slow)
- usually when fast contraction velocity is required
- makes more mechanical sense this way because slow fibres are inefficient at fast contraction velocities
what do muscle spindles sense and which afferents sense each
position - slow adapting II afferents
velocity - fast adapting Ia afferents
what reflex are muscle spindles responsible for
stretch reflex
