20 - Physiology 3 Flashcards
What should I know?
- Different types of muscle contraction
- (DRAW) force-length and force-velocity relationship and relate to power output
- Energetics of contraction
- Myasthenia Gravis and Duchennes Muscular dystrophy
- Define muscle fatigue and causes
What is isometric contraction?
> NO external shortening takes place
> force of the weight = the force developed by the muscle
What is isotonic contraction?
> movement takes place
there is a mismatch between the tension generated by the contracting muscle and the load and so the muscle changes length
What are the 2 types of isotonic contraction?
Eccentric - muscle actively lengthens as load>muscle
Concentric - muscle actively shortens as muscle>load
Isotonic Concentric Contraction
> shorten
muscle force>load force
lifting a weight, cycling, swimming, push up
Isotonic Eccentric Contraction
> lengthen as resists load
muscle force < load force
climbing down a mountain, running down a hill, downwards motion of a push up, uncurling a bicep controlled
What type of muscle contraction causes a lot of Delayed Onset Muscle Soreness (DOMS)?
Eccentric (lengthening)
> strengthening exercises involve eccentric contractions
> they cause a lot of damage, injury and soreness
How is muscle growth aided?
Eccentric muscle damage causes the release of cytokines that may aid muscle growth
What are isolated muscle studies?
> Muscles put at a fixed length and an electrical stimulus is applied to the muscle by electrodes to initiate contraction
can measure the force produced by a muscle at different fixed lengths
Describe the Force - Length Relationship
> force developing cross bridges are formed in the region of filament overlap
when the muscle is stretched there is less filament overlap so force decreases as length increases
when you decrease the length there is an interaction between thin filaments, thick filaments and the Z Discs so force decreases
there is an optimal length where there is an optimal/maximal formation of X Bridges as myosin heads are opposite actin binding sites
What is the optimal length of sarcomeres?
2.1-2.2 um
We subconciously move our muscles to this length
What is the passive force component of the total force of muscle contraction?
- the applied force to stretch muscle
- the passive force reflects the elastic properties of the CT matrix (and cytoskeleton)
Relationship between passive and active force?
- reciprocal
- passive force increases and active force decreases and length increases
What is the active force?
The twitch force
How is the force-length relationship predicted?
With the Sliding Filament Theory
What is the current theory for Delayed Onset Muscles Soreness (DOMS)?
> that not all sarcomeres lengthen evenly during eccentric contraction
once a sarcomere gives way it will be massively stretched and so will develop less force
the weakest sarcomeres in series will LENGTHEN FIRST in eccentric contraction and give way first leading to the ‘popping sarcomere theory’
Describe the Force-Velocity Relationship
- as load increases the velocity the muscle shortens should decrease
If the load on a muscle is constant then the velocity of shortening should be…
Constant. This is isotonic contraction.
Isometric contraction…
> Occurs when the maximum force developed by the cross bridges is balanced by the applied force
there is no movement and so there is no velocity
no velocity or distance moved so no power output by the muscle
Eccentric contraction…
force applied ? X bridge resulting in the muscle stretching
How do you calculate the power output of a muscle?
F = ma Work (J) = Fd Power (W) = work/time = Fd/time = Force x Velocity > power is dependent on the rate of muscle shortening
How do you calculate the power of an isometric contraction?
No movement
No work
No power
When is maximum force developed?
Fo/optimal force is developed when there is no shortening = isometric contraction