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a.With the aid of diagrams provide a summary of how the following energy systems
work.
Energy systems; introduction
Energy systems are cellular levels processes used to produce Adenosine Triphosphate
(ATP) figure 1. This is an adenosine molecule linked to three high-energy phosphates
that acts as an energy store for the cell. The energy is released when ATPase, an enzyme,
reacts with ATP to produce ADP and Pi, e.g.
ATP ADP + Pi
There are three energy systems that do this;
·The Creatine Phosphate System
·The Glycolytic or Lactic Acid system
·The Oxidative system (The Krebs cycle, Citric Acid Cycle or Tricarboxylic Acid Cycle)
The first too are ANAEROBIC, the third is AEROBIC.
I.Creatine Phosphate (CrP)
Summary: A cytoplasm based catabolic reaction in which Creatine Phosphate is degraded
to Creatine to provide ATP; net profit of one ATP molecule; can proceed anaerobically.
Net reaction:
CrP + ADP+H+---<ATP + Creatine
Detail:
During high-intensity exercise energy for ATP resynthesis is provided primarily by
another high-energy phosphate compound called creatine phosphate (CrP), see figure 2.
Cellular concentrations of CrP are 4-5 times greater than that of ATP and are generally
concentrated in areas of contractile protein; skeletal muscle has 95%. CrP is like a match;
when the muscle receives a nerve impulse from the brain instructing it to contract, it
instantly releases its energy, as if the match had been struck.
This gives a natural "reservoir" of energy to enable resynthesis of ATP to occur rapidly,
7Toler (1997), 8Vandenberghe (1996) and 9Feldman (1999), but it can only sustain work
at maximal levels for about 5 - 15 seconds dependant on activity level and the
individual's personal physiological adaptations to exercise.
The system has two steps. Firstly, bond between creatine and phosphate splits energy is
liberated, as CrP has a higher potential energy than ATP, sufficient energy is released to
resynthesise ADP to ATP. This reaction is catalysed by the enzyme creatine kinase.
CrP Cr + Pi + energy
The energy created in the split's useless to the cell directly; so in step two it's used to
convert ADP and Phosphate to ATP and thus a source of useable energy to the cell. The
process of ATP-CrP regeneration is the most rapid pathway for providing muscular
energy.
Energy
ADP + Pi ------------------< ATP
This is a 1:1 ratio in that one Creatine phosphate delivers one ATP molecule. This is not a
very efficient system but it's very fast; the chemical name for Creatine is N(aminoiminomethyl)-N-methyl glycine or methylglycocyamine, figure 3. It's synthesized
in the liver, pancreas, and kidney from the three amino acids - L-Arginine, Glycine and
L-Methionine. Following its biosynthesis, creatine is transported to the skeletal muscles,
heart, brain, and other tissues where it's phosphorylated (the red area in figure 3) and
stored. This allows the muscle cells to have about a 15 second energy source on tap that
does not require oxygen to be used, during maximal exercise.
Very fast sports, e.g. the 100m sprint, powerlifting, are based almost totally on this
energy system, (see table 2 page 13).
II.Glycolysis - the Lactic Acid System.
Summary: A series of cytoplasm based catabolic reactions in which glucose is degraded
to pyruvate (pyruvic acid) to provide ATP and NADH (nicotinamide adenine
dinucleotide) as well as molecules for the anabolic pathways; net profit of two ATP
molecules; hydrogen is released; can proceed anaerobically.
Net reaction:
Glucose + 2 ADP + 2 Pi + 2 NAD+---<2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
Detail:
Glycolysis, also called the Embden-Myerhoff pathway, is the sequence of reactions,
which converts a glucose molecule into two pyruvate molecules with the production of
NADH and ATP. Specific enzymes control each of the different reactions, as shown in
figure 5. Glucose comes either directly from digestion, or from short-term storage in the
muscles or long-term storage in the liver. There is a net gain of two (2) ATP at the end of
glycolysis (reaction shown above), using glucose as the source and three (3) from
glycogen. This is because glucose needs to be converted to glucose 6-phosphate to enter
the glycolytic pathway that requires the use of one ATP, (see figure 4).
All the reactions of glycolysis take place entirely in the cytosol due to the abundance of
free-floating ingredients such as ADP, NAD+, and inorganic phosphates. Glycolysis
itself does not require oxygen and can proceed under both aerobic and anaerobic
conditions.
Glycolysis can generally be divided into two main phases. Phase one encompasses the
first four steps of glycolysis, see figure 5. During this first phase, phosphate is added to
the glucose molecule. The glucose molecule is now split into two three-carbon
glyceraldehyde-3-phosphate (PGAL) molecules. This phase of glycolysis cannot occur
without the input of energy and phosphate from two molecules of ATP.
In the second phase of glycolysis (steps 6-10 in figure 5), energy harvesting begins,
firstly with the reduction of NAD+ to NADH by the oxidation of PGAL, storing some of
the energy from glucose in NADH's energy rich electrons and secondly enough energy is
released to add a second phosphate group to PGAL, forming 1,3-bisphosphoglyceric acid.
At this point, glycolysis is finally ready to make ATP. Substrate-level phosphorylation
occurs when one of the phosphates of 1,3-bisphosphoglyceric acid is transferred to ADP.
The three-carbon molecule that remains is then rearranged to form phosphoenolpyruvic
acid, becoming pyruvate when it gives up its phosphate to a second ADP. In this way,
each PGAL from the first half of glycolysis is used to make two molecules of ATP and
one molecule of pyruvic acid.
Through glycolysis, a small amount of the chemical energy that started out in glucose
ends up in ATP and NADH, about 5% of it; most of the energy remains in pyruvate,
which under aerobic conditions is used to either make more ATP in the mitochondria via
the Krebs cycle or under anaerobic conditions builds up as lactate.
The system supports moderate and high intensity exercise that lasts for up to 45 seconds
or so.
Other sugars can be catabolised by glycolysis via their conversion to molecules that can
be fed into the pathway in its first phase:
·Fructose ----< 2 glyceraldehyde 3-phosphate
·Lactose --< glucose + galactose,
·Galactose --< glucose 1-phosphate --< glucose 6-phosphate
·Mannose ---< mannose 6-phosphate --< fructose 6-phosphate
During periods when glycolytic metabolism exceeds oxidative phosphorylation (Krebs
cycle and the electron transport chain) glycolysis's end product; lactate, is passed to the
blood and thence to the Liver where it's converted back to glucose; under a process called
gluconeogenesis and thence back to the blood and cells as fuel. This is known as the Cori
cycle, or lactic acid cycle.
III. Aerobic System (Krebs cycle) using 1. Carbohydrate and 2. Fat.
1.Carbohydrate
Summary: The degradation (oxidation) of the 2-carbon acetyl group of acetyl coenzymeA (acetyl-CoA) through a cyclic sequence called the Krebs cycle (KC). Carbohydrate
enters the cycle through the conversion of one glucose molecule to two pyruvate
molecules that are then in turn converted to two molecules of acetyl-CoA. Fatty acids are
readily used in the system and this is covered in section 2 below. Electrons in the
oxidations are transferred to NAD and to FAD, and a pyrophosphate bond is generated in
the form of guanosine triphosphate (GTP). This high-energy phosphate is readily
transferred to ADP to form ATP. As Figure 6 illustrates, this is a truly continuous cycle.
Net reaction:
Acetyl-CoA + 2H2O + 3NAD+ + Pi + GDP + FAD ---<2CO2 + 3NADH + GTP + CoASH + FADH2 + 2H+
Details:
Krebs cycle (KC) or the Citric Acid Cycle (CAC) or Tricarboxylic Acid Cycle (TCA),
occurs in mitochondria and is the final common catabolic pathway to completely oxidise
fuel molecules (monosaccharides and free fatty acids (FFAs)) under aerobic conditions.
Sir Hans Krebs worked out the details of the cycle in the 1930's. Two carbons enter the
cycle as acetyl-CoA and two carbons leave as CO2. In the course of the cycle, four
oxidation-reduction reactions take place to yield reduction potential in the form of three
molecules of NADH and one molecule of FADH2. A high-energy phosphate bond (GTP)
is also formed.
Pyruvate, the product of anaerobic glycolysis, is produced in the cytosol. It's moved into
the mitochondrial matrix by active transport where it's used to form acetyl-CoA by
oxidative decarboxylation; this forms the link between aerobic and anaerobic
carbohydrate catabolism and thus is also termed 'the common degradation product'.
The first reaction of the cycle occurs when acetyl-CoA transfers its two-carbon acetyl
group to the four-carbon compound oxaloacetate, forming citrate, a six-carbon
compound. The citrate then goes through a series of chemical transformations, losing first
one and then a second carboxyl group as carbon dioxide. Most of the energy made
available by the oxidative steps of the cycle is transferred as energy-rich electrons to
NAD+, forming NADH. For each acetyl group that enters the KC, three molecules of
NAD+ are reduced to NADH. In Step 6, electrons are transferred to the electron acceptor
FAD rather than to NAD+. Because two acetyl-CoA molecules result from each glucose,
the cycle must turn twice to process each molecule. At the end of each turn of the cycle,
the four-carbon oxaloacetate is left, and the cycle is ready for another turn. Only four
moles of ATP are produced directly by a substrate-level phosphorylation with each turn
of the KC, this is not much more than the two moles from glycolysis. The rest of the ATP
that is formed during aerobic respiration is produced by the electron transport system and
chemiosmosis see figure 7.
2.Fat
Summary: The process of fatty acid (FA) oxidation is termed b-oxidation (beta oxidation)
since it occurs through the sequential removal of 2-carbon units by oxidation at the bcarbon position of the fatty acyl-CoA molecule. Each round of b-oxidation produces one
mole of NADH, one mole of FADH2 and one mole of acetyl-CoA, which then enters the
KC, and under goes the reactions as described above. The oxidation of FAs yields
significantly more energy per carbon than carbohydrates; b-oxidation of one mole of
oleic acid (18-carbon FA) yields 146 moles of ATP; ~441 molecules, compared with 114
moles from 18 glucose carbon atoms.
Net reaction: Each reaction is specific to the length of the carbon backbone of the fat
involved; the overall reaction for the b-oxidation of palmitic acid (palmitoyl-CoA) may
be written as follows:
C16-SCoA + 7 FAD + 7 NAD+ + 7 H2O + 7 CoASH 8 Acetyl-CoA + 7 FADH2 + 7
NADH + 7 H+
Detail:
Fatty acids are a major source of energy for most tissues. The first step in their utilization
is by beta-oxidation of fatty acyl-CoAs. In this process the size of the fatty acy-lCoA is
reduced in a sequence of steps. A sequence of four enzymatic reactions splits the
molecule at the single CC bond between the (alpha) and (beta) carbons, hence betaoxidation. Fat is a highly concentrated energy source. Muscle is the main tissue that burns
(oxidises) fat. High rates of fat oxidation (fat oxidation phase/ FO phase) occur during the
later stages of aerobic exercise; the exact point at which it begins cannot be specified
because as transition from the Lactate Phase to the FO Phase is gradual. It's important to
note that in order to obtain energy efficiently from fat, glucose must be burned
simultaneously, hence the expression: "Fat burns in the fires of glucose."
The primary sources of fatty acids (FAs) for b-oxidation are dietary and mobilisation
from cellular stores. FAs from the diet can are delivered from the gut to cells via
transport in the blood. FAs are primarily stored as triacylglycerols within adipocytes of
adipose tissue. In response to energy demands, they can be mobilised for use by
peripheral tissues. This release is controlled by a complex series of interrelated cascades
that result in the activation of hormone-sensitive lipase.
The stimulus to activate this cascade, in adipocytes, can be glucagon, epinephrine or bcorticotropin. These hormones bind cell-surface receptors that are coupled to the
activation of adenylate cyclase upon ligand binding. The resultant increase in cAMP
leads to activation of protein kinase A (PKA), which in turn phosphorylates and activates
hormone-sensitive lipase. This hydrolyses FAs at carbons 1 or 3. The resulting
diacylglycerols are substrates for either hormone-sensitive lipase or for the non-inducible
enzyme diacylglycerol lipase. Finally the monoacylglycerols are substrates for
monoacylglycerol lipase. The net result of the action of these enzymes is three moles of
free fatty acid (FFA) and one mole of glycerol. The FFAs diffuse from adipose cells,
combine with albumin in the blood, and are thereby transported to other tissues, where
they passively diffuse into cells.
b.Explain when the different systems might be used in the body
The cells of the body utilise the breakdown of ATP to liberate energy to then undertake
the functions necessary for life. There is only a limited supply of ATP in the body at any
time, roughly 85g, as such only a few seconds (&10 seconds) of maximal energy release,
and thus muscular work, can occur 'on tap', i.e. instantaneously at any one time. It's not
really known why the body has such low ATP stores, however, it's quite heavy and the
average sedentary person uses an amount of ATP equivalent to 75% of their body weight
each day, so small amounts with rapid resynthesis is probably good, or we'd all be 75%
heavier than our current weight, 10Houston (2001).
To maintain energy release ADP must be resynthesised to ATP on a regular basis within
each cell as it's used, and the resynthesis occurs within a specific metabolic pathway, the
selection of which is dependent upon the volume and mode of exercise performed, i.e. the
intensity. In general the higher the volume, and more isometric the mode then the more
reliance on aerobic based energy pathways as the both the Creatine and the glycolytic
systems become exhausted relatively quickly as energy reservoirs.
Carbohydrate is a crucial fuel for exercise and its main supplier into the blood is the liver
- either directly from its own glucose store (glycogen) or by turning fat and protein into
glucose ('gluconeogenesis'). However, the snag is that only limited amounts of glycogen
can be stored in the liver and muscles (table 1). The liver weighs only about 2kg,
compared to the body muscle mass; weighing 10-20 times this, as such hard working
muscles could totally deplete blood glucose in a few minutes. Simply, the liver can
nowhere near supply glucose at a rate that the muscle can utilise.
Table 1: The body's Fuel stores
gkcal
Carbohydrate
Liver glycogen110451
Muscle glycogen2501025
Glucose in body fluids1562
Total3751538
Fat
Subcutaneous780070980
Intramuscularly1611465
Total796172445
11Adapted from Wilmore " Costill (1999).
Thus, to protect the blood levels of glucose, and to protect the glucose supply to the brain
(the brain is highly susceptible to low blood glucose as it's virtually the only fuel it uses
and it doesn't have it's own stores) and other peripheral tissues, muscle has somehow to
be prevented from exhausting the blood glucose. And the method whereby this is done is
threefold:
·first, muscle is given a good store of glucose as glycogen;
·second, muscle is prevented from using much glucose directly from the blood during
muscular work; and
·third, muscle is switched over to the massive fat energy store as soon as the glycogen /
blood glucose runs low.
Thus as exercise intensity or duration increases, the contribution of the aerobic system to
energy production initially decreases as the glycolytic system and the CrP system are
used, this creates a characteristic continuum curve shown in figure 9, but then increases
with their exhaustion and within the aerobic system, fat becomes an increasingly
important energy source. Table 2 gives varying dependencies on the three systems and in
Figure 10 an illustrated example is given.
As the rate of energy extraction from fat is much lower than carbohydrate, 5Journal of
Applied Physiology, more oxygen is required to gain the same amount of energy, and
hence more blood needs to be supplied, which in turn requires a higher heart rate. Since
circulation is improved as a result of training, better fat utilisation is possible because of
that increased supply,15Fox " Bowers.
Table2; Dependency of various sports activates on the different energy systems.
ActivityDependence on:Time DurationHrs:mins:secs
Creatine PhosphateGlycolyticMitochondrial
Kicking a ballHighLowLow0:0:05
Power liftingHighModerateLow0:0:05
Throwing EventsHighLowLow0:0:10
Running up stairsHighLowLow0:0:10
Pole VaultingHighModerateLow0:0:10
Jumping EventsHighLowLow0:0:10
100-200m SprintHighModerateLow0:0:10-0:0:30
50-100m SwimHighModerateLow0:0:10-0:0:30
Internal LiftingHighModerateLow0:0:30-0:2:00
400-800m SprintHighHighModerate0:0:60-0:3:00
200-400 m SwimHighHighModerate0:2:00-0:5:00
1500m run ModerateModerateHigh0:3:30-0:6:00
5-10k runLowLowHigh0:12:00-0.30:00
Marathon Low LowHigh2:0:00-4:0:00
Source: 17Cavangh " Kram (1985)
There are a number of artificial means by which the fuel for exercise can be altered which
for completeness of answer are summarised in table 3 below.
Table 3: Artificial means of altering the fuel balance for exercise.
1The ingestion of caffeine in sufficient quantities (about 5 mg/kg of body weight) can
cause free fatty acid levels to peak after about 60 minutes and remain elevated for about
three hours at about three to four times that of normal levels. The effect is delayed by
about two hours if sugar is also taken at the same time.
2The drug Heparin has similar properties to that of caffeine. Although it has been used in
an attempt to extend endurance performances, research has not been consistent in
replicating the effects and benefits that it's suggested to produce.
3A high carbohydrate meal causes blood insulin to rise and stay elevated for 60 to 90
minutes. Since insulin inhibits performance because it slows free fatty acid mobilization
and the breakdown of glycogen in the liver, the body has to rely primarily on muscle
glycogen and a small amount of glucose in the blood for energy. Those sources are used
rapidly, hypoglycaemia could result (evidenced by dizziness, a feeling of weakness, or
nausea), and endurance is reduced. 2Foster and Costill (1978) found reductions of 19
percent in endurance capacity in subjects who ingested 75 grams of glucose prior to
performing a maximum exercise at 80 percent of VO2max. This would suggest it's not
wise to ingest any form of carbohydrate within two hours before a performance. This no
longer is generally recommended although it's necessary for individuals who are
susceptible to reactive hypoglycaemia. Thus, testing for reactivity in athletes is important
so that the best precompetition regimen can be established.
4The ingestion of glucose or carbohydrates during exercise can marginally prolong
performance. It has no effect on muscle glycogen but it does spare the use of liver
glycogen if it can be assimilated into the circulatory system in time. The rate of emptying
from the stomach and absorption into the blood stream determine the value of this
supplement. Emptying is facilitated by the glucose being diluted as a cool drink taken in
resting or calm circumstances.
5The rate of muscle glycogen use appears to be increased in hot conditions.
6However the body's athletic conditioning also plays a role in what fuel is chosen. Firstly
specific training can be done to increase the creatine system and also to condition the
muscles to resist the effects of lactic acid build-up from the glycolytic system. In addition
as specific athletic fitness alters the call on fat versus carbohydrate oxidation and
glycogen depletion is stalled, 2Foster " Costill (1978). In addition regular training
increases the total number of mitochondria in the muscles, thus making the 'battery' they
provide larger, this not only improves endurance, 12Holloszy (1975) but delays the need
to switch to fat, 13Holloszy (1967) and 14Dudley (1975), making muscle more efficient
at a given intensity.
Adapted by A. J. Whalley from various sources.
Keywords:
with diagrams provide summary following energy systems work energy systems
introduction energy systems cellular levels processes used produce adenosine
triphosphate figure this adenosine molecule linked three high phosphates that acts store
cell released when atpase enzyme reacts with produce there three that this creatine
phosphate system glycolytic lactic acid system oxidative system krebs cycle citric acid
cycle tricarboxylic acid cycle first anaerobic third aerobic creatine phosphate summary
cytoplasm based catabolic reaction which creatine phosphate degraded provide profit
molecule proceed anaerobically reaction detail during high intensity exercise resynthesis
provided primarily another high compound called figure cellular concentrations times
greater than that generally concentrated areas contractile protein skeletal muscle like
match when muscle receives nerve impulse from brain instructing contract instantly
releases match been struck this gives natural reservoir enable resynthesis occur rapidly
toler vandenberghe feldman only sustain work maximal levels about seconds dependant
activity level individual personal physiological adaptations exercise steps firstly bond
between splits liberated higher potential than sufficient released resynthesise reaction
catalysed enzyme kinase created split useless cell directly step used convert thus source
useable cell process regeneration most rapid pathway providing muscular ratio delivers
molecule very efficient very fast chemical name aminoiminomethyl methyl glycine
methylglycocyamine figure synthesized liver pancreas kidney from three amino acids
arginine glycine methionine following biosynthesis transported skeletal muscles heart
brain other tissues where phosphorylated area stored allows muscle cells have about
second source does require oxygen used during maximal exercise very fast sports sprint
powerlifting based almost totally table page glycolysis lactic summary series cytoplasm
based catabolic reactions which glucose degraded pyruvate pyruvic provide nadh
nicotinamide adenine dinucleotide well molecules anabolic pathways profit molecules
hydrogen released proceed anaerobically glucose pyruvate nadh detail glycolysis also
called embden myerhoff pathway sequence reactions which converts glucose into
pyruvate molecules with production nadh specific enzymes control each different
reactions shown comes either directly from digestion short term storage muscles long
term storage liver there gain glycolysis shown above using source glycogen because
needs converted enter glycolytic pathway requires take place entirely cytosol abundance
free floating ingredients such inorganic phosphates itself does require oxygen proceed
under both aerobic anaerobic conditions generally divided into main phases phase
encompasses first four steps during first phase added split into carbon glyceraldehyde
pgal phase cannot occur without input second steps harvesting begins firstly reduction
oxidation pgal storing some rich electrons secondly enough second group pgal forming
bisphosphoglyceric point finally ready make substrate level phosphorylation occurs when
phosphates bisphosphoglyceric transferred carbon remains then rearranged form
phosphoenolpyruvic becoming gives each half make pyruvic through small amount
chemical started ends about most remains under aerobic conditions either make more
mitochondria krebs under anaerobic conditions builds lactate supports moderate intensity
lasts seconds other sugars catabolised their conversion fructose glyceraldehyde lactose
galactose galactose mannose mannose fructose periods glycolytic metabolism exceeds
oxidative phosphorylation krebs electron transport chain product lactate passed blood
thence liver where converted back process called gluconeogenesis thence back blood
cells fuel known cori lactic using carbohydrate carbohydrate degradation oxidation
carbon acetyl group acetyl coenzyme acetyl through cyclic sequence carbohydrate enters
through conversion then turn converted fatty acids readily covered section below
electrons oxidations transferred pyrophosphate bond generated form guanosine
triphosphate readily transferred form illustrates truly continuous fadh details citric
tricarboxylic occurs mitochondria final common catabolic completely oxidise fuel
monosaccharides free fatty acids ffas hans worked details carbons enter carbons leave
course four oxidation reduction take place yield reduction potential fadh bond also
formed product produced cytosol moved mitochondrial matrix active transport where
oxidative decarboxylation forms link between catabolism thus also termed common
degradation product occurs transfers group four compound oxaloacetate forming citrate
compound citrate then goes series chemical transformations losing carboxyl dioxide most
made available rich electrons forming each enters reduced step electron acceptor rather
than because result must turn twice process turn oxaloacetate left ready another only
moles produced directly substrate level phosphorylation much more moles rest formed
respiration produced electron transport chemiosmosis fatty termed beta since sequential
removal units position acyl round produces mole mole fadh mole enters goes described
above yields significantly more carbohydrates oleic yields moles compared atoms
specific length backbone involved overall palmitic palmitoyl written follows scoa coash
detail major tissues step their utilization beta acyl coas size lcoa reduced sequence
enzymatic splits single between alpha beta carbons hence highly concentrated main tissue
burns oxidises rates occur later stages exact point begins cannot specified because
transition lactate gradual important note order obtain efficiently must burned
simultaneously hence expression burns fires primary sources dietary mobilisation cellular
stores diet delivered cells blood primarily stored triacylglycerols within adipocytes
adipose tissue response demands they mobilised peripheral tissues release controlled
complex series interrelated cascades result activation hormone sensitive lipase stimulus
activate cascade adipocytes glucagon epinephrine corticotropin these hormones bind
surface receptors coupled activation adenylate cyclase upon ligand binding resultant
increase camp leads activation protein kinase phosphorylates activates hormone sensitive
lipase hydrolyses resulting diacylglycerols substrates either hormone sensitive lipase
inducible enzyme diacylglycerol finally monoacylglycerols substrates monoacylglycerol
result action these enzymes free glycerol ffas diffuse adipose combine albumin thereby
transported other they passively diffuse explain different might body body utilise
breakdown liberate undertake functions necessary life there only limited supply body
time roughly such seconds maximal release thus muscular work instantaneously time
really known such stores however quite heavy average sedentary person uses amount
equivalent their weight small amounts rapid resynthesis probably good heavier current
weight houston maintain release must resynthesised regular basis within within specific
metabolic selection dependent upon volume mode performed intensity general higher
volume isometric mode reliance pathways both become exhausted relatively quickly
reservoirs crucial fuel main supplier store glycogen turning protein gluconeogenesis
however snag limited amounts glycogen stored muscles table weighs compared mass
weighing times hard working could totally deplete minutes simply nowhere near supply
rate utilise table stores gkcal fluids total subcutaneous intramuscularly total adapted
wilmore costill protect levels protect supply brain highly susceptible virtually uses doesn
have peripheral somehow prevented exhausting method whereby done threefold given
good store prevented using much muscular third switched over massive soon runs
duration increases contribution production initially decreases creates characteristic
continuum curve shown increases exhaustion becomes increasingly important gives
varying dependencies illustrated example given rate extraction much lower journal
applied physiology oxygen required gain same amount hence needs supplied requires
higher heart rate since circulation improved training better utilisation possible increased
bowers dependency various sports activates different activitydependence time durationhrs
mins secs phosphateglycolyticmitochondrial kicking ballhighlowlow power
liftinghighmoderatelow throwing eventshighlowlow running stairshighlowlow pole
vaultinghighmoderatelow jumping eventshighlowlow sprinthighmoderatelow
swimhighmoderatelow internal liftinghighmoderatelow sprinthighhighmoderate
swimhighhighmoderate moderatemoderatehigh runlowlowhigh marathon lowhigh
cavangh kram number artificial means altered completeness answer summarised below
artificial means altering balance ingestion caffeine sufficient quantities weight cause peak
after minutes remain elevated hours times normal effect delayed hours sugar taken same
drug heparin similar properties caffeine although been attempt extend endurance
performances research been consistent replicating effects benefits suggested produce
meal causes insulin rise stay elevated minutes since insulin inhibits performance slows
mobilization breakdown rely primarily small those sources rapidly hypoglycaemia could
evidenced dizziness feeling weakness nausea endurance reduced foster costill found
reductions percent endurance capacity subjects ingested grams prior performing
maximum percent would suggest wise ingest hours before performance longer generally
recommended although necessary individuals susceptible reactive hypoglycaemia testing
reactivity athletes important best precompetition regimen established ingestion
carbohydrates marginally prolong performance effect does spare assimilated circulatory
emptying stomach absorption stream determine value supplement emptying facilitated
being diluted cool drink taken resting calm circumstances appears increased however
athletic conditioning plays role what chosen firstly training done increase condition resist
effects build addition athletic fitness alters call versus depletion stalled foster costill
addition regular training increases total number mitochondria making battery they larger
improves holloszy delays need switch holloszy dudley making efficient given adapted
whalley various sources
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