Determinants of Strength/Power Flashcards
What mechanisms best explain the linear relationship between muscle volume and power?
With increasing muscle volume, there are more sarcomeres in parallel within the muscle. This enables more cross bridge connections to occur simultaneously during contraction and increases force output.
Furthermore, more sarcomeres in series increases muscle fibre length. With greater length, a muscle will shorten a large distance in a given duration, thus having a greater velocity.
What was the r value during Powell et al. (1984) study measuring force and muscle CSA in guinea pig hind limbs?
r= 0.98
Strong linear relationship between muscle CSA and force
What is the gold standard method for measuring muscle CSA?
MRI
describe the findings of Banman et al. (2000) when analysing the relationship between MRI CSA and plantar flexor isometric strength?
A broad relationship was found
r= 0.73 Rsquared= 0.54
54% of the variability in strength can be explained by plantar flexor CSA
around 50% has been reported in several other studies
What are the two measures of muscle architecture?
Length of the muscle fascicles
Angle of pennation compared to the line of action (tendon to tendon)
How is muscle architecture assessed?
Using Ultrasound
What were the findings of Kumagai et al. (2000) when comparing muscle architecture amongst sprinters?
Longer fascicle lengths were found in sprinters with quicker sprint times.
Why is power influenced by muscle volume?
Power = force x velocity
- Force is proportinate to muscle CSA
- Velocity is dependant on fascicle length
thus, power is proportionate to muscle volume
What are the optimal pennation angles for isometric force and velocity? and for power?
What were the key take aways from the slide?
For velocity, the angle is 0
for force, the optimal angle is 45
when determining pennation angle for force, using PCSA (perpendicular to the line of the fibre length) is more appropriate.
- having pennate muscle fibres allows more fibres within a given muscle size.
- however, to much pennation decreases the force applied to the line of action
- thus there is a trade off between greater fibre CSA and decreased force applied to the line of action.
The optimal pennation angle for power = somewhere between 0 and 45
What were the key take aways from the comparison between type I and type IIx muscle fibres in the slides?
Type IIx fibres have x2 shortening velocity compared to type I
Pmax, the optimum fibre shortening velocity for maximal power is different between muscle fibre types.
Type IIx fibres can generate 9x more power than type I
thus has major advantage in power based tasks.
What is ATPase? and how does this relate to muscle fibre type?
Force cross bridge cycling to occur quickly, myosin heads need to be able to break down ATP quickly. This depends on concentration of the enzyme ATPase.
The more ATPase, the faster the power stroke will occur, the fast the cross bridge cycle will occur, the faster the sarcomere will shorten and ultimately the higher shortening velocity in the muscle fibre.
Higher concentrations of ATPase is what makes fast twitch muscle fibres ‘fast’
What were the findings Baxter and Piazza (2014) when comparing moment arm and strength?
Moment arm explains to some extent the strength of plantar flexor muscles (R2= 0.31)
However, moment arm was also correlated with muscle volume (r2= 0.19)
But further analysis revealed moment arm explained 13% of the variance in strength once muscle volume was accounted for.
