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
