Muscle Metabolism Flashcards
Skeletal muscle fibers are classified based on two major characteristics. What are they?
- Maximum shortening velocity
- Major pathway used for ATP synthesis
What is the maximum shortening velocity?
The degree of myosin ATPase activity found in the muscle fiber
Type 1 fibers are […] in speed
Slow
Type 2 fibers are […] in speed
Fast
What are the 2 major ways that muscle cells generate ATP?
Oxidative phosphorylation
Glycolysis
Glycolytic Fibers
- Mitochondrial density is […]
- […] and […] are the major fuel storage molecules
- […] capillary density
- […] levels of myoglobin
- […] susceptible to fatigue
- […] in color
- Low
- creatine phosphate and glycogen
- Lower
- Lower
- More
- White
Oxidative Fibers
- […] mitochondrial density
- […] is the major form of fuel storage
- […] capillary density
- […] levels of myoglobin
- […] susceptible to fatigue
- […] in color
- Higher
- Triglycerides
- Higher
- Higher
- Less
- Red
What is myoglobin?
The oxygen binding protein found in cardiac and skeletal muscle. Its purpose is to speed up the delivery of oxygen from the blood to the mitochondria.
How many binding sites does myoglobin have for oxygen?
One
What are the 3 types of muscle fibers?
Type 1 = fast, oxidative
Type 2a = fast, mixture of oxidative and glycolytic
Type 2x = fast, glycolytic
In response to a single action potential:
- Fast muscles develop tension and relax […]
- Slow muscles develop tension and relax […]
- Quickly
- Slowly
In response to a train of action potentials:
- Slow muscles exhibit […] at lower stimulation frequencies
Summation
This graph is showing the order in which the types of muscles are recruited in response to a stimulus. Which line represents type 1 and type 2?
Are type 1 or type 2 muscle fibers recruited first for a movemet in response to stimulus?
Type 1
Which type of muscle fatigues more quickly: type 1 or type 2?
Type 2
Are muscles ever purely type 1 or purely type 2 fibers?
No - they contain a variable mix of fiber types which gives an average result of performance (more type 1 or more type 2 character or almost equal mix of both)
What determines the distribution of fiber types in a person’s muscles?
- Gender (men more type 2)
- Genetics
What are the effects of training on muscle fibers?
- Hypertrophy (alters muscle fiber size, when you gain muscle your fibers grow in size instead of adding more fibers)
- Alters capacity for ATP production
- May or may not change fiber type
What is the effect of high intensity and low repetition exercise?
What is the effect of low intensity, high repetition exercise?
What is this graph showing?
With exercise training, there is a shift in type 2 fibers from fast to slow fiber types. This happens to make muscle fibers more fatigue resistant.
Is it possible to change the fiber type makeup of your muscles (i.e. switch from more type 1 fibers to more type 2 fibers)?
Yes, but it is a very slow process and takes years of consistent training to develop. Detraining causes a reversion back to unexercised state, which is largely driven by genetics.
Other than exercise, what other factors play a role in determining what type of fibers are present in muscles?
- Neuromuscular activity
- Unloading/inactivity
- Aging
How does innervation play a role in determine the type of fibers present in a muscle?
- Fast firing, fast conducting, high threshold neurons innervate fast muscle fibers.
- Slower firing, slower conducting, lower threshold neurons innervate slow muscle fibers
All muscle fibers in a motor unit are the […] type
Same
Slow motor units tend to be […] in size
Smaller
Fast motor units tend to be […] in size
Larger
ATP is required for muscle contraction. What are the 3 potential sources of ATP in a muscle cell?
Which of these are anaerobic?
Oxidative phosphorylation
Glycolysis (anaerobic)
Creatine Phosphate (anaerobic)
What is creatine phosphate used for in muscle?
FAST generation of ATP
Creatine phosphate + ADP –> ATP + creatine (catalyzed via creatine kinase)
CP store is 5x that of ATP in muscle
When is creatine phosphate used during exercise?
Very important at the start for quick burst of energy
Why is creatine kinase used as a marker for muscle injury?
It is abundant in muscle, small in size, and often leaks out of damaged cells.
What happens in a muscle cell if the pace of glycolysis outpaces that of the TCA cycle?
NAD+ will be depleted, resulting in build up of NADH which will shut off TCA cycle. To reverse this and turn TCA back on, cell can shuttle pyruvate into cori cycle to make lactate via lactate dehydrogenase (regenerates NAD+).
True or false: The body produces lactic acid during exercise.
FALSE
Pyruvate is converted to lactate. If any lactic acid were produced in the body it would rapidly deprotonate b/c its pKa is lower than that of the environment
True or false: lactate is a waste product.
FALSE
It is used in the cori cycle to regenerate NAD+ to continue glycolysis and TCA and it can enter gluconeogenesis.
True or False: Lactate causes acidosis and fatigue.
False
ATP hydrolysis releases H+ and is the primary cause of acidosis in muscles during high intensity exercise. Therefore, lactate production is a consequence of acidosis not the cause of it. Lactate actually can temporarily buffer acidosis to an extent.
True or false: lactate causes muscle soreness.
FALSE
Lactate removal from muscle is rapid (< 1 minute) following exercise. Additionally, power athletes do not experience delayed onset muscle soreness (DOMS) every time they workout, which you would expect they would if lactate were the culprit of DOMS.
What causes DOMS?
- Intense exercise in muscles that are unaccustomed to being worked
- Eccentric contractions
- Microscopic tears in muscle fibers
- Excessive Ca2+ release
What is meant when we say that muscle operates with an oxygen debt?
Oxygen uptake (and oxidative phosphorylation) lags behind energy expenditure at the onset of exercise. Therefore, other fuel sources must be utilized for ATP generation. At the end of exercise, those initial sources of ATP must be regenerated (CP, lactate, pyruvate, etc.)
What are these graphs showing?
That heavy, exhausting exercise activates your metabolism for a longer period of time after termination than moderate exercise
Label image with correct source of ATP for contraction:
- Creatine phosphate + free ATP
- Anaerobic glycolysis - muscle glycogen
- Aerobic oxidation - liver glycogen, muscle glycogen, plasma glucose
- Aerobic oxidation - plasma FFA, adipose tissue TAGs
- What type of exercise is best for burning fat and for how long do you need to do it to preferentially burn fat?
- Why does this time threshold need to be met for this effect to be observed?
- Aerobic exercise; Greater than 30 minutes
- Epinephrine increases during prolonged exercise and it activates hormone sensitive lipase which liberates FFAs from adipose tissue and releases into the blood
What is this graph showing?
That as exercise intensity goes up (increasing VO2 max), the source of fuel tends toward carbohydrates instead of fats.
What is this graph showing?
That as exercise intensity increases, the amount of fuel derived from the plasma (FFA and glucose) decreases and the amount of fuel derived from the muscle stores itself increases.
What is the definition of muscle fatigue?
The inability to matinain force or power output during repeated muscular contractions or during a single prolonged contraction.
What will be the onset and cause of fatigue in short duration, more intense exercise?
Acute onset
Due to accumulation of protons and inorganic phosphate (from ATP hydrolysis)
What will be the onset and cause of fatigue in long duration, less intense exercise?
Slow onset
Due to fuel depletion
