Term
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Definition
| Inability to generate force during repeated contraction. |
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Term
| What's the difference between central and peripheral fatigue? |
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Definition
| Central fatigue = CNS involvement. Peripheral fatigue = fatigue as a result of actual physiological changes in nerves, muscles, and neuromuscular junctions. |
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Term
| what are some things that contribute to central fatigue? |
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Definition
| Emotion, motivation, distraction. |
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Term
| Metabolite depletion in the muscle fiber can contribute to peripheral fatigue. A decrease in what metabolites can cause the problem? (4) |
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Definition
| PCr, ATP free energy, Glycogen, Blood Glucose. |
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Term
| Compare the decrease in PCr and ATP with activity. |
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Definition
| PCr takes an initial steep decline at the onset of activity, then demonstrates a more gradual decline until rest, at which point it rises again. ATP takes an initial moderate drop, then plateaus during activity, and rises again to resting levels soon after the concusion of activity. |
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Term
| What is compartmentalization? |
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Definition
| Looking at a 'bigger' picture (compartment) because we don't have the technology to look at things more closely, like where a substrate has its activity. |
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Term
| The theory of compartmentalization attempts to explain what phenomenon? |
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Definition
| ATP does not drop in concert with, or as much as, PCr with activity. |
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Term
| Describe why there might be a decline in the amount of energy that ATP releases. |
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Definition
| Increased H concentration (decreased pH) may inhibit the ability of ATP to release all of its potential energy, resulting in the same amount of ATP present in the blood, but not the same amount of energy to show for it. (so ATP binding to myosin is affected, but overall ATP content is not affected greatly; therefore the plateau in ATP levels with activity) |
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Term
| When would you expect glycogen depetion to occur? |
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Definition
| After prolonged submaximal exercise. |
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Term
| Glycogen depletion is fiber type specific. What does this mean? |
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Definition
| That depending on the rate of exercise and the muscles you are recruiting, glycogen depletion with change in the given muscle types accordingly. |
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Term
| How are the different muscle types affected by glycogen depletion with: moderate rate (60RPM), High intensity low resistance, and High intensity high resistance activities? |
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Definition
| Moderate: Both fiber types are uniformly depleted. High intens/low resist: Type one more depleted than type 2. High intense/high resist: type 2 more depleted than type 1.Glycogen remains stored in adjacent fibers in teh same muscle. |
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Term
| With what type of exercise will blood glucose become depleted? |
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Definition
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Term
| What things contribute to a decline in blood glucose? |
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Definition
| Redistribution of blood flow (decreaseed perfusion to gut, including liver which regenerates glucose, decreased precursors get to the liver to make more glucose, and decreased transport of glucose FROM the liver to the muscles where it's needed.) So the altered blood flow pattern may inhibit production and transportation of new glucose that muscles need to keep from feeling fatigued. |
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Term
| A decline in blood glucose has peripheral as well as central fatigue effects. What are the central effects? |
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Definition
| Decreased blood glucose --> decreased glucose to the CNS --> increased perception of fatigue because decreased glucose is an irritant to the CNS in a general way, which leads to decreased performance. |
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Term
| What is it, specifically, about lactic acid accumulation what we think may be a cause of fatigue? |
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Definition
| the increase in hydrogen ion. |
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Term
| there are two basic "Compartmentalized" theories as to why ATP doesn't drop as much as PCr with activity. What are they? |
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Definition
| That there is a down-regulation of contractile force to preserve ATP for more vital functions (protective mechanism). The same amount of ATP is present, but it may not be releasing the same amount of energy as it normally would be. |
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Term
| What major impacts does increased [H] have that might contribute to fatigue?(5) |
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Definition
| Inhibits PFK, Interferes w/ binding of Ca to troponin (therefore actin/myosin coupling), Stimulates pain receptors, inhibits O2/Hb, Interferes w/ lipase. |
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Term
| How does inhibition of PFK (by increased H ion) affect fatigue? |
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Definition
| Inhibition of PFK (rate limiting enzyme) decreases the speed of glycolysis --> decreased speed of blood glucose regeneration. |
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Term
| Increased hydrogen ion stimulates pain receptors. How is it thought that this might contribute to fatigue? |
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Definition
| Pain is a general irritant, which leads to inhibition of muscle contraction. |
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Term
| Increased H ion interferes w/ lipase (release of FFAs). How does this impact fatigue? |
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Definition
| It forces a shift in energy dependence from lipids to glycolysis, which has a decreased effectiveness because of PFK inhibition. |
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Term
| Lactic Acid is an indicator of three major things. What are they? |
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Definition
| That there is increased H ion in the blood and muscle, a general indication that there's an inability to clear waste products, and that the subject is entering glycogen depletion range. |
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Term
| What is phosphate accumulation caused by, and how does it contribute to fatigue? |
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Definition
| It's leftover from ATP breakdown, and it inhibits PFK, displaces Ca on troponin and may act synergistically w/ H ion. |
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Term
| Calcium is essential to muscle contraction. But when it accumlates, it begins a chain of events that leads up to contribution to fatigue. Outline this process. |
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Definition
| Slow Ca reuptake into sarcoplasmuc reticulum w/ repeated contraction --> depressed Ca --> ATPase activity --> less able to relax. Mitochondria take up Ca from cytoplasm because they're trying to keep the cytoplasm Ca in balance, Removal of the Ca from mitochondria requires ATP, which means there's less ATP available to drive muscle contraction. Release of fresh Ca from sarcoplasmic reticulum decreases w/ repeated contractions. The Ca floating around in the cytoplasm isn't as effective for energy production as fresh Ca from the SR, so energy production decreases. To top it all of, there is decreased sensitivity of actin and myosin to Ca w/ repeated contractions, which further impacts a decrease in energy release and therefore muscle contraction. Whew! |
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Term
| Is the story stronger for the contribution of H ion accumulation, or O2 depletion to fatigue? |
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Definition
| H ion accumulation has more supporting evidence. |
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Term
| What are most likely the main culprits, currently identified, to skeletal muscle fatigue? |
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Definition
| H and phosphate accumulation, along with CNS effects. |
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Term
| How do we measure muscle fatigue? |
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Definition
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Term
| What change do you see in EMG w/ fatigue? |
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Definition
| You see more power at a low frequency. Peak power occurs at a lower frequency, and centroid frequency is decreased. |
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Term
| What is centroid frequency? |
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Definition
| The point on an EMG at which half the power is above and half the power is below that frequency. |
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Term
| What happens to centroid frequency w/ fatigue? |
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Definition
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Term
| What are the parameters commonly used on EMG to assess fatigue? (4) |
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Definition
| Increased amp of low frequency component, Decreased am of high freq component, Decreased high to low frequency ratio, and decreased centroid frequency. |
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