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2.Ex Phys week 9.

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winniesmith2's version from 2018-04-30 12:46

Section 1

Question Answer
Physiological definition of fatigue Failure to maintain the required or expected force or power
definition of weakness Failure to generate the required or expected force or power
describe stimulatiom of a muscle in vivofatigued muscle generates less force but over a longer period of time than a fatigued muscle.
Can we determine whether fatigue is located centrally or peripherally? If yes, how?by electrically shocking muscle before and after an intervention, to eliminate brain influence.
What energy is required during muscle work energy for excitation-contraction coupling; an ATP dependent process. used for – Myosin head force development – Na+, K+-ATPase (3 Na+ out, 2 K+ in) ( resting potential) – Calcium pump. In an energy crisis, or if enzyme activities drop, these processes could impair performance.
What does repeated contractions show about force and calciumthat they may be connected in some way, the more contractions, the less force and the less calcium. (graphs page 2). Type 2 less calcium, fatigue faster.
What is the effect of caffeine on Ca2+ handling. Caffeine facilitates opening of ryanodine receptors in sarcoplasmatic reticulum (SR) membrane, releasing calcium
How can we measure inhibitory effects on Ca2+ releaseisolate muscle, then add Mg2+, high AMP and ADP, very low ATP (2-8mmol/L artificially low ATP) (all products associated with fatigue), causes Ca2+ release to decrease.
Why does Mg2+ concentration increase as concentration doubles at fatigue as ADP, AMP and IMP have lower affinity for Mg2+ than ATP.
Describe Ca2+ re-uptake evidence in amphibians only that this is the cause for slower relaxation of the muscle.
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Section 2

Question Answer
Describe ATP depletion • Many studies have reported that ATP in a cell does not drop below 60% of resting levels (whole muscle!) • Isolated fibres: down to 20%. Localised ATP is also possible in space between T tubule and SR (triad junction) - ATP may be more depleted towards the edges. could this effect the calcium pumps and Na+ K+ pumps in these areas.
Describe why Na+, K+ ATPase activity is depressed at fatigueThe Na+, K+ ATPase powers the Na+, K+ pump (to restore the resting potential of a cell following an action potential)
How might fatigue affect potassium gradients Accumulation of K+ in extracellular space – T tubular membrane: large surface – T tubular network: small volume  Rapid K+ accumulation • More difficult to induce action potentials. Increased K+ content, fibre is less able to produce action potential waves.
describe effect of inorganic phosphatemay be another candidate to induce fatigue. As ATP goes down Pi goes up. Inorganic phosphate can bind with calcium to form calcium phosphate (CaHPO4) and reduce the amount of free calcium.
Skip last 2 slides of page 3pH, force and calcium and H ions for blame.
is pH a factor for fatigueno, can not alone effect fatigue, importance of physiological range.
Why can decrease in pH not explain fatigue alone– Some studies show muscle fatigue at only very moderate drops of pH (from 7.05 to 6.8) – Long-lasting activity: little or no acidosis! (for example marathon) – Force typically recovers much faster than pH (Allen et al., 2008) – Activation of Ca2+ release not noticeably inhibited even at pH 6.2 – Patients with McArdle’s disease don’t accumulate H+ but do fatigue
What is compartmentalisation metabolite concentrations vary within different compartments of the cell!
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Section 3

Question Answer
What is the effect of glycogen on fatigue glycogen is a fuel. no fuel -> no power. Glycogen is an essential substrate. Training has an effect on fat oxidation- better at oxidising fat, better at saving carbohydrates.
Glycogen depletion and time to fatigue• During work, the muscle glycogen falls successively to values approaching zero, and the working capacity decreases when the glycogen store is depleted.
effect of CHO feedingcycling to fatigue at 71% VO2 max. one group with placebo one with CHO. CHO group kept going for an hour longer.
why do we fatigue when CHO is being fed continuously?unknown, could be any factors previously mentioned.
Glycogen depletion study cycling to exhaustion with depleted glycogen stores (low CHO diet for 4 days) when glycogen depleted, go for less time, pump activity rates decreased.
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