Week 5 Flashcards
What does contraction lead to?
Muscle tension
Define muscle tension
The Force generated by contracting muscle
Define load
The external force exerted on the muscle
Can be influenced by:
- external load + gravity
- body weight + gravity
- another muscle
What happens when tension is greater than the load?
There will be a concentric contraction and the muscle length will shorten
What happens when tension is less than load?
There will be an eccentric contraction and muscle length will lengthen
What happens when tension is equal to load?
There will be an isovolumetric contraction and muscle length will stay the same
What is a dynamic contraction and what are its two subcategories?
A dynamic contraction is one that moves the skeleton
two subcategories:
1. Isotonic: tension stays the same throughout contraction (velocity changes)
2. Isokinetic: velocity stays the same throughout contraction (tension changes)
What is a static contraction?
A contraction where no movement occurs - isometric
What results from more crossbridges?
More tension
What does max tension differ between?
- movements due to mechanical factors
- muscles due to morphological factors
- contractions due to neural factors
- physiological contexts (nutritional status, fatigue, etc…)
- people
What are 3 mechanical factors that influence muscle tension
- Contraction velocity
- Muscle action
- Joint angle
Draw and explain the contraction velocity graph on page 4 of muscle tension I
In terms of strength, what is strongest for muscle contractions
Eccentric > isometric > concentric
How does joint angle affect tension?
Joint position (aka joint angle) influences muscle length
What else influences the relationship between force and angle other than muscle length?
- other biomechanical factors
- type of joint/level
- location of muscle insertion
- length of limb segments
- morphological factors
- xc area, pennation angle
- individual factors
- age, sex, training status
- fatigue
What are the strongest contractions usually?
- mechanically optimal
- morphologically optimal
- neurally optimal
- metabolically optimal
- psychologically optimal
- in a body that is not experiencing fatigue
What is fatigue?
The inability to maintain a power output or force during any type of repeated or sustained muscle contractions
Why is understanding mechanisms of fatigue important?
- to prevent/delay it in critical situations
- to improve fatigue resistance through training
- to optimize recovery in critical situations
- to improve recovery rate/process through training
What are the peripheral factors of fatigue (mainly local effects)
- phosphagen depletion
- substrate depletion
- metabolite accumulation/ion imbalance
What are the central factors of fatigue (global effects)
- psychological factors
- central and peripheral neural factors
- oxygen supply
Describe depletion of phosphagens in terms of fatigue
THE PRIMARY FATIGUE MECHANISM FOR PHOSPHAGEN SYSTEM
ATP and PCr deplete during very high intensity activity
- ATP can deplete to 40% of resting values
- PCr can deplete to 15% of resting values
To recover, ATP and PCr must be replenished
For half time, this takes ~20-25 seconds and for full time this takes 3-5 minutes
Describe the accumulation of metabolites/ion imbalance in terms of fatigue
PRIMARY FATIGUE MECHANISM FOR ANAEROBIC LACTIC SYSTEM
Many metabolites/ions can interfere with ATP synthesis and/or muscle contraction when their quantities are too high/too low
Ex: H+, Ca2+, Ammonia/ammonium, Na+/K+, Pi
In order to recover, the body needs to reset
For half time, recovery takes ~5-8 mins and for full time, recovery takes 12-20 mins
Describe substrate depletion (glycogen) in terms of fatigue
PRIMARY FATIGUE MECHANISM FOR AEROBIC SYSTEM
- reduces rate of glycolysis which leads to reduced pyruvate available for CAC which means reduced ATP resynthesis
- fat is probably available but fat burns in a CHO flame - can’t make oxaloacetate without burning CHO
- reduces ability to maintain blood glucose concentration
- can lead to CNS impairment/loss of coordination
- bonking or hitting the wall
In order to recover, the muscle glycogen must be replaced
For half time, recovery takes ~5-6 hours w/ proper nutrition and for full time, recovery takes 1-2 days
Describe neural fatigue in terms of central AND peripheral
POSSIBLE FATIGUE MECHANISM FOR ANY/ALL SYSTEMS
Central:
- occurs in brain and spinal cord
- loss of motivation and/or concentration
- reduced motor drive
- pain intolerance
Peripheral:
- occurs at neuromuscular junction
- decreased muscle excitability
what are 3 morphological factors that influence muscle tension?
- cross-sectional area
- pennation angle
- muscle fiber type
what does endurance mean
the ability to sustain/repeat contractions
what relationship will there always be between force/power and duration/endurance
there will always be an inverse relationship
what is max tension directly proportional to
muscle cross-sectional area (CSA)
at the level of the muscle fiber, what does bigger muscle fibers mean?
- more myofibrils
- more myofilaments (actin + myosin)
- more possible cross-bridges
at the level of the muscle, what does bigger muscles mean
could mean bigger muscle fibers and/or MORE muscle fibers (+ more connective tissue)
- more actin + myosin
- more possible cross-bridges
what does physiological cross-sectional area depend on?
the arrangement of fibers
- fascicles are arranged differently in different muscles
- in pennate muscle, fascicles attach obliquely to tendon
- direction of tension is oblique to tendon
increased pennation angle means more fibers pulling in the direction of tension which means more potential cross-bridges
- there is a tradeoff with shortening potential / velocity
what can muscle fiber types be categorized according to?
contractile properties
- slow twitch (type I)
- fast twitch (type II)
metabolic properties
- oxidative (aerobic)
- oxidative/glycolytic (both)
- glycolytic (anaerobic)
what are fibers typed via
- muscle biopsy
- staining
complete the tables on page 6 of muscle tension II
complete the table on page 8 of muscle tension II
can we make muscles stronger? if so how?
Yes we can make muscles stronger
- strength gains related to dose of training
- increased gains over time
- increased gains with increased time under tension
- increased gains with increased intensity (increased load)
- gains of 25-100% are common
- gains evident at:
- whole muscle level
- single fiber level
gains are specific to muscle groups that are trained
can we make muscles bigger?
Yes we can make muscles bigger
- muscle CAS increases 7-15% within 10-14 weeks
- training leads to hypertrophy
what does fiber hypertrophy include?
- increased size and number of myofibrils
- increased contractile protein (more XBs = more tension)
- increased connective tissue
what is hypertrophy specific to?
muscle fiber types that are trained
can we increase pennation angle?
yes we can
adaptations are specific to muscles that are trained
can we convert fiber types into the type we want?
no we cant
fiber type distribution is genetically-determined and varies from muscle to muscle (highest % SO in postural muscles)
we cant turn slow-twitch fibers into fast-twitch fibers or vice versa
we CAN make FG better at oxidative metabolism
- FOG -> FG
complete the table on page 11 of muscle tension II
complete table on page 12 of muscle tension II
