Sport Science Practical Report Assignment | Get Paper Help

a practical report use given data need draw graphs with ExcelEXSS3061 Exercise Responses and Programming Faculty of Medicine and Health Sciences,
The University of Sydney
Oxidizing carbohydrates and fats during exercise
Tom Gwinn, Faculty of Medicine and Health Sciences, The University of Sydney
1) Structure of fuels in the body: carbohydrate and fat
Although carbohydrates (CHO) exist in many forms, in this section we will only consider glucose as
this represents the sole type of carbohydrate that is oxidised as a fuel. So when the term carbohydrate is
used in the context of a fuel for exercise we are specifically referring to either glucose (or its storage
form: glycogen). Similarly although fats exit in different forms in the body, here we will only consider
long-chain fatty acids (FA) and their storage form as triglycerides.
• Glucose is a monosaccharide. Its formula
can be simply represented as C6H12O6.
Shown at right is open-chain form of
glucose. When dissolved in water it tends
to form a ring structure shown at far right.
• Fatty acids are carboxylic acids with long hydrocarbon tails. Fatty acids that are stored in the body
and used as fuel typically have carbon chain lengths of between 16 to 18. Three typical fatty acids
are shown below. Palmitic acid will be used in later examples as a representative fatty acid.
2) The majority of whole body oxygen
consumption during exercise is consumed by
muscle
At rest skeletal muscle oxygen consumption accounts
for about 30% of the total whole body oxygen
consumption. During exercise this percentage
increases dramatically so that at 𝑉 ̇
O2max for either a
sedentary subject or a well-trained athlete, the muscle
𝑉 ̇
O2max accounts for approximately 95% of the whole
body
.
V O2max . Thus when we measure a whole body
exercise 𝑉 ̇
O2 it is a reasonable approximation to
consider this as representing the rate of muscle oxygen
consumption.
Figure 2 Distribution of
.
V O2to locomotor muscles, heart
and other tissue at rest and during maximal exercise in a
sedentary subject and in an endurance-trained athlete.
(Adapted from Hoppeler H and Weibel ER. 1998)
stearic acid (C18)
palmitic acid (C16)
oleic acid (C18)
Rest O2max
sedentary
athlete
2
3) Muscle oxygen consumption measures the rate of muscle fuel oxidation
The complete oxidation of carbohydrate and fat provides the majority of the energy necessary for our
metabolism at rest and the energy necessary for all forms of prolonged (steady state) exercise.
The general relationship for the combustion of any carbon fuel, whether it be petrol, ethanol,
carbohydrate or fat, is:
carbon fuel + oxygen → carbon dioxide + water + energy
Since the two fuels oxidised during exercise are carbohydrate and fat1, we can say that during exercise
the following two overall reactions occur at the same time:
carbohydrate + oxygen → carbon dioxide + water + energy
and
fat + oxygen → carbon dioxide + water + energy
(Note: These are unbalanced equations, the balanced equations are shown below in equations 1 & 2)
These two reactions are the only source of consumption of molecular oxygen from the atmosphere, so
during exercise (and rest) we can say that the rate of whole body rate of oxygen consumption (
.
V O2 ) is
simply the sum of the rate that oxygen is consumed during the oxidation of carbohydrate (
.
V O2 CHO ) and
the rate that oxygen is consumed during the oxidation of fat (
.
V O2 fat ), i.e.
.
V O2 =
.
V O2 CHO +
.
V O2 fat
Similarly at rest and during exercise at low to moderate intensities the following is also true2:
.
V CO2 =
.
V CO2 CHO +
.
V CO2 fat
4) Carbohydrates and fats releases similar amounts of energy per litre of oxygen consumed
Different fuels produce different amounts of energy (per molecule of mole) and consume O2 and produce
CO2 in different ratios. The specific stoichiometric relationship for each fuel can be determined by
burning a known quantity of the fuel in a bomb calorimeter. The relationships for the complete oxidation
of glucose and palmitic acid (a typical free fatty acid used by the body) are:
Glucose: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 2,823 kJ/mole (equation 1)
Palmitate C15H31COOH + 23 O2 → 16 CO2 + 16 H2O + 10,024 kJ/mole (equation 2)
The energy values shown here are the enthalpy changes ° which are also known as the heat of
combustion. From these equations we can determine how much energy is released when we consume a
litre of O2.
From equations 1 and 2 it is clear that there is a fixed relationship between the amount of oxygen
consumed and the amount of energy released when oxidising carbohydrate of fat.
1 Proteins can be oxidized to provide energy, and provide a significant proportion of total energy supply during severe
starvation. However during most forms of exercise by well-nourished subjects, protein oxidation forms only a minor
contribution to total energy supply, and we will ignore protein oxidation throughout this discussion.
2 During intense exercise there is a net production by muscle of H+ ions which diffuse from the muscle into the blood, which
tends to increase the acidity of the blood. In order to minimize the change in blood pH there is a buffer system in the blood –
the carbonic anhydrase system. This enzyme catalyses the reaction between bicarbonate (HCO3
-) and H+ as follows:
HCO3
– + H+ → H2CO3 → H2O + CO2
Thus during intense exercise in addition to metabolic sources of CO2 production (i.e. from CHO and fat oxidation) there is an
additional source of CO2 production from buffering. Thus during intense exercise
.
V CO2 =
.
V CO2 CHO+
.
V CO2 fat +
.
V CO2 buffering
So during high-intensity exercise the RER may be greater than 1.0.
EXSS3061 Exercise Responses and Programming Faculty of Medicine and Health Sciences,
The University of Sydney
• We can see that if we were exclusively oxidising glucose then
6
2823
kJ are released for each
mole of O2 we consume. However using units of moles is quite an inconvenient way to quantify
amounts of gas. A fixed number of gas molecules (e.g. a mole) will occupy a known volume
of under standard conditions (pressure and temperature). A mole of oxygen or carbon dioxide
occupies 22.4 litres STPD. So when we consume 1 litre of O2 while oxidising glucose then we
have released
6
2823
kJ per mole of O2/ 22.4 litres per mole = 21.0 kJ per litre of O2 consumed.
• If we were exclusively oxidising fat then
23
10,02 4
kJ are released for each mole of O2
consumed. So when we consume 1 litre of O2 while oxidising fat then we have released
23
10,024
kJ per mole of O2/ 22.4 litres per mole = 19.5 kJ per litre of O2 consumed.
These numbers are quite similar so that, as an approximation, we generally calculate that during exercise
when a person consumes a litre of O2 them have expended 21 kJ of energy.
(You might ask why not use a value between 21 and 19.5? The reason is that during exercise the majority
of energy come from CHO oxidation).
5) The ratio of energy from CHO vs fat oxidation can be determined from the RER
Under various exercise conditions it is an important question to ask: Of the total energy expended, what
proportion of the energy is provided from carbohydrate oxidation and what proportion is provided from
fat oxidation? This question can be answered by measuring the ratio of CO2 production to O2
consumption, i.e.
The balanced for glucose oxidation is:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
So if carbohydrate is the sole fuel being oxidised, then the ratio is
6
6
= 1.0
The balanced equation for the oxidation of the fatty acid palmitate is:
C15H31COOH + 23 O2 → 16 CO2 + 16 H2O
So if palmitate is the sole fuel being oxidised, then the ratio is
23
16
= 0.71
Thus the RER can be thought of as a sliding scale where a value of 1 indicates that the 100% of the
energy is being derived from carbohydrate oxidation, a RER of 0.7 indicates that the 100% of the energy
is being derived from fat oxidation, and RER values between 1.0 and 0.7 indicate that a mixture of
carbohydrates and fats are being oxidised simultaneously.
The calculation the fuel mixture can be done using a table such as the one provided in Appendix 1.
During intense exercise the RER can exceed 1.0. The reason for this is explained in Note 2 above.
When the RER exceeds 1.0 during we assume that 100% of energy expenditure comes from CHO
oxidation and 0% comes from fat oxidation.
References
Hoppeler H and Weibel ER. Limits for oxygen and substrate transport in mammals. J Exp Biology 201,
1051–1064, 1998
Peronnet F and Massicote D. Table of nonprotein respiratory quotient: an update. Can J Sport Sci 16:
23–29, 1991
CO2
O2
CO2
O2
CO2
O2
4
Appendix 1
Table of Nonprotein Respiratory Exchange Ratio
From: Peronnet F and Massicote D. Table of nonprotein respiratory quotient: an update. Can J Sport Sci 16: 23–29, 1991
Percentages of energyPercentages of energyPercentages of energy from from fromRERCHOFatRERCHOFatRERCHOFat0.703601000.80034.565.50.90068.631.40.7050.599.50.80536.263.80.90570.329.70.7102.397.70.81038620.91071.928.10.7154.295.80.81539.760.30.91573.626.40.7206940.82041.458.60.92075.324.70.7257.892.20.82543.256.80.92576.923.10.7309.690.40.83044.955.10.93078.621.40.73511.488.60.83546.653.40.93580.219.80.74013.286.80.84048.351.70.94081.818.20.74515850.84550500.94583.516.50.75016.883.20.85051.748.30.95085.114.90.75518.681.40.85553.446.60.95586.713.30.76020.479.60.86055.144.90.96088.411.60.76522.177.90.86556.843.20.96590100.77023.976.10.87058.541.50.97091.68.40.77525.774.30.87560.239.80.97593.26.80.78027.472.60.88061.938.10.98094.85.20.78529.270.80.88563.636.40.98596.43.60.79031690.89065.334.70.9909820.79532.767.30.89566.933.10.99599.60.40.9961000