Module 6 - Muscle Force-Velocity Relationship Flashcards
What does the force-length relationship describe?
- Sarcomere or muscle behaviour at a constant length
What do most daily activities involve?
- Muscle shortening or lengthening
What describes daily activities better force-length or force-velocity relationship?
- Force-velocity relationship
What does the force-velocity relationship describe?
- Force generated by a muscle as a function of velocity under constant load (isotonic)
What is the most important dynamic property of muscles?
- Force-Velocity relationship
Is the force-velocity relationship linked to a specific anatomical structure?
- No
What does the force-velocity relationship describe?
- Muscle force under concentric isometric and eccentric muscle actions
What happens during a concentric action?
- Lift a load smaller than max
- Isometric tension generated
- Muscle shortens
- Force smaller than P0
- As load increases, velocity decreases
What happens during an eccentric action?
- Load is larger than the max
- Isometric tension generated
- Muscle lengthens
- Force larger than P0
- Absolute tension independent of volocity
What is larger? tension for eccentric action or concentric action
- Eccentric Action
What is the force-velocity relationship for concentric action?
- Force drops rapidly as velocity increases (50%Fmax, 17%Vmax)
What are the therapeutic implications of the force-velocity relationship of a concentric action?
- Muscles are strengthened at least partly based on force placed across them
- Exercise at high velocity imply muscles are contracting with low force
What is a general rule to improve strengthening with concentric action?
- Keep velocity low
What might high velocity do for concentric action?
- Improve muscle activation by CNS
What is common following eccentric action exercise?
- Muscle soreness
- INjury
What are the greatest muscle-strengthening techniques?
- Eccentric Action exercise
- Maximum Force
Why might eccentric exercise be a good option for those with breathing disorders?
- low energic cost
- High force generation
- improves muscle force generation
What issues might arise from eccentric exercise?
- Delayed Onset Muscle System (DOMS)
What must be done with eccentric exercise to limit DOMS?
- Magnitude and Duration increases gradually
What does the active force during the concentric action of a muscle depend on?
- Total number of cross-bridge connections between actin and myosin
What does the cross-bridge model account for during eccentric action?
- can account for increased force
- The proportion of attached cross-bridges increases
- cross-bridges distribution distances increase
What can the cross-bridge model not explain in eccentric forces?
- Force increase for slow stretching velocities
- energy requirements are overestimated
Are isometric strength and muscle velocity the same thing?
NO
- two distinct muscular abilities
What must we be careful about when examining a patient?
- the test we choose to evaluate strength
What are the tests to test strength?
- one repetition maxima
vs - Maximal Isometric force at a specific joint angle
What are the domains of muscular strength testing?
- Static
- Dynamic
- Explosive
- Stoppin
What corresponds closely with force-velocity relationship?
- Domains of muscular strength testing
Does the shape of force-velocity curve change with training?
No
- Can be shifted upwards (towards Fmax)
- Rightward (towards Vmax)
What does an upward shift in force-velocity curve mean?
- Movement towards Fmax
What does a rightward shift in force-velocity curve mean?
- Movement towards Vmax
What would athletes maximizing movement speed train with?
- lower weights
- Higher speeds of movement
What would athletes who are maximizing force output train with?
- Higher weights
- Lower repetitions
What part of the muscle does the force-velocity relationship correlate with?
- Whole Muscle
What are the effects of muscle length between two muscles with identical physiological cross-sectional area?
- Increases Vmax
- Peak tension developed by the muscle remains the same
What does a muscle with a longer fiber have?
- more sarcomeres arranged in series
What do longer muscle fibers with more sarcomeres arranged in series have?
- slower sarcomere shortening velocity (for same muscle shortening velocity)
What is the force-velocity profile of predominantly FF motor units (FG fibers) compared to S motor units (SO fibers)?
Given same number of sarcomeres in series
- Generate greater velocity of shortening for FF motor units
What is the peak tension of FF motor units?
- 25-50ms
What is the peak tension of S motor Units?
- 60-120ms
According to the force-length-velocity relationship, why would muscle force change?
- Change in length
- Change in velocity
Why are the force-length and force-velocity relationships fairly unrealistic?
They require the force at:
- constant length
OR
- constant load
What can the force-length-velocity relationship estimate?
- Muscle force produced when both length and velocity change
When the muscle shortening velocity is high, like in concentric action, how will force be affected?
The force will be low
- irrespective of muscle length
What is an important force modulator at low concentric velocities?
- Muscle Length
What dominates length as a determinant of muscle force for slow-lengthening velocities like in eccentric actions?
- Muscle Velocity
What does strength training do to muscles?
- Makes them intrinsically slower
What is larger from strength training the hypertrophy of Slow Oxidative fibers or Fast-glycolytic fibers?
- Slow-Oxidative Fibers
What might happen to slow fibers following strength training?
- Increase in proportion
Compare the shortening time of fast muscle fibers to slow muscle fibers when accounting for muscle length differences
- Fast muscle fibers shorten 2-3 times faster than slow muscle fibers
What does strength training do relative to PCSA and maximal force?
- Increase both
Why would you recommend strength training for high-level sprinters?
- Decrease in Muscle Velocity correlates to an Increase in Muscle Force
What is the equation for power?
P = F * V
P = Power
F = Force
V = Velocity
What can increasing muscle force do?
- Increase Muscle Power
When does power reach its peak during muscle shortening?
- Around 30-50% velocity
When does peak power not occur?
At either extreme of
- Force
- Velocity
What is running speed correlated with?
Muscular and Structural Factors
- Percentage of fast-twitch fibers
- Length of muscle fascicles