Lecture 16 Flashcards
Measuring Energy and Substrate Usage
best way of measuring energy usage
VO2 and VCO2
we are not 100% efficient at converting chemical energy into mechanical energy, how energy is lost as heat
~2/3 of energy lost as heat just to make ATP oxidatively
what is calorimetry
the measurement of metabolic energy transformation
if you are not doing anything energy will be released as ….
heat
if you are doing something energy will be released as …
heat and mechanical energy
what is mechanical energy and how can it be measured
work rate
measurable using ergometers or estimations
what form of calorimetry is a bomb calorimeter
direct calorimetry
how does a bomb calorimeter work
measures energy released from combustion of food
who is a bomb calorimeter useful for
useful for nutrition and dietetics
what is a bomb calorimeter not useful for
- clinical exercise physioloigy
- sport exercise physiology
- ergonomics
what form of calorimetry is whole body calorimeter
direct calorimetry
how does whole body calorimeter work
measures body heat production, uses an insulated room
who is a whole body calorimeter useful for
useful for nutrition, dietetics, clinical exercise physiology and research
what are disadvantages for whole body calorimeter
- expensive
- requires specialist expertise
- restrictive (type of activity and limited time resolution)
what type of calorimetry is open circuit spirometry
indirect
how does open circuit spirometry work (O2)
indirectly measure rate of energy use by measuring rate of O2 consumed (VO2L.min-1)
disadvantages to open circuit spirometry
- doesn’t give instantaneous energy usage
- only useful is steady state
- expensive
per L of oxygen which provides more energy, carbs or fat (what is the % difference)
carbohydrates
6% less energy coming from fat than CHO, per L of oxygen
if you are unfit or exercising at an intensity too high for you what source of fuel are you most likely to use more of
switch to using more carbohydrates as it provides you more energy faster (glycolysis) also because it gives you more energy per L of oxygen
why are you able to use fats as a fuel source for longer if you are fitter
not as O2 limited
how does open circuit spirometry work (O2 and CO2)
indirectly measure rate of energy use by measuring rate of O2 consumed and CO2 produced (VCO2L.min-1)
what does the ratio of carbon produced per unit oxygen consumed indicate (2)
- whether some energy is not from aerobic metabolism (R>1.00)
- relative use of Fat vs CHO being metabolised
how do you know the relative use of Fat vs CHO being metabolised
different substrates (food groups) produce different of carbon dioxide when they are oxidised
what is the respiratory quotient
RQ = VCO2 / VO2
what is the respiratory quotient for carbohydrate metabolism
1.00
for every 6 O2 used, 6 CO2 produced
what is the respiratory quotient for fat metabolism
0.70
for every 23 O2 used, 16 CO2 produced
what are the three things you must consider when estimating caloric equivalent from RER
- respiratory quotient is at cellular level
- RER reflects RQ only with aerobic metabolism - steady state
- RER > 1.00 reflects loss of CO2 from non oxidative source
what is meant by respiratory quotient is at cellular level in terms of estimating caloric equivalent from RER
assume that same as respiratory exchange ratio (RER) measured at the mouth
what is the difference between absolute and relative fat and CHO usage (what does it show about fat metabolism adaptation)
you can adapt your fat burning enzymes etc from sprint as well as you can during mutli hour exercise
so this means we don’t know what the best training intensities are for burning fat
does HR vs VO2 relationship differ between people
yes
what is an issue with predicting VO2 and energy usage from work rate
can be inaccurate, especially with differences in efficiency
