Energy systems and balance Flashcards
What are the 3 categories of biological work?
- Mechanical (e.g. muscle contraction)
- Chemical (e.g. glucose – glycogen)
- Transport (e.g. active transport)
How de we re-synthesize ATP in the immediate, short and long term?
immediate: ATP-PCr system
short term: glycolytic system
long-term: oxidative system
Roughly how much energy is lost during ATP synthesis as heat?
60-70%
Describe the two methods of studying metabolism
Direct calorimetry: measures heat
Indirect calorimetry: measures O2 intake and CO2 production
What is the formula for respiratory exchange ratio (RER)?
VCO2/VO2
What use is RER and what are the standard values you may observe?
RER gives an indication of substrate mix
usually between 0.7 and 1
RER > 1 when one is hyperventilating or undergoing intense exercise
What happens to substrate utilisation as exercise intensity increases?
More CHO utilised than fat.
The crossover point occurs at about 50% of VO2 max.
- (Venables et al, 2005)
Muscle glycogen provides majority of energy above 65% VO2 max, taking over from plasma FFA.
- (Romjin et al, 1993)
Energy balance = ?
energy intake - total energy expenditure
What makes up energy expenditure?
> physical activity (15-45%)
DIT (10%)
BMR/RMR (50-75%)
What explains the majority of variance in BMR within humans?
fat free mass (~63%)
- (Johnstone et al, 2005)
Physical activity level (PAL)?
total energy expenditure / BMR
How does direct calorimetry measure energy expenditure?
measures heat loss from participant
What are some issues associated with direct calorimetry?
X can’t monitor rapid changes
X can’t determine fuel use
X space limitations
X exercise equipment = friction = heat
How do indirect calorimetry methods measure energy expenditure?
measuring O2 consumption and CO2 production
What are some issues associated with indirect calorimetry?
X measuring affecting behaviour
X difficulty in long term use
X difficult outside of lab
How could you perform indirect calorimetry over a period of days?
> Doubly labeled water
> self report / recall
How does doubly labelled water work?
Uses heavy stable isotopes 2H and 18O.
H lost as H2O, but O lost as H2O AND CO2.
The difference in rates of elimination is used to estimate CO2 production.
Critique doubly labelled water
X expensive
X expertise and equipment required
X no info about substrate use
X no short term use (7-14 days)
How are self-report and recall measures utilised for the purposes of indirect calorimetry?
activity diaries utilising ~15 minute periods throughout the day to register and activity or MET score
What are some issues with using self-report and recall measures?
X recall issues
X time-consuming for ppt and experimenter
X not sensitive
Give some examples of non calorimetric methods of assessing energy expenditure and their pros/cons
> Pedometer + accelerometers:
$ cheap and accessible
$ good for ambulatory activity
X misses static activity (e.g. lifting or cycling)
> HR monitors
$ accessible
$ based on fairly linear relationship between HR and EE
X HR affected by other factors (e.g. stress)
X Poorer at lower intensities
X HR is highly variable between people
> Multi-sensort devices
$ multiple sensors reduces the error influence of a singular device
What is an issue associated with physical activity wearables?
Can vary greatly between activities.
The error of different bands varies, therefore can’t compare between them.
- (Chowdhury et al, 2017)
How would you establish the total energy of food?
combustion
What are 3 methods of assessing energy intake?
> What are some issues with these methods?
- food diaries
- food recall questionnaire
- weighing food + fluid intake
> 1, 2 and 3 are time-consuming in the process and analysis.
1, 2 and 3 also may lead to Hawthorne effect (altering behaviours due to being observed)
1 and 2 are open to recall errors
What’s the upper limit for acute energy expenditure?
~23XRMR when running 4 minute miles.
for very short periods of time, very high energy expenditures can be achieved
- (Ainsworth et al, 2011)
In the short term, can energy intake or expenditure be higher?
acute energy intake > energy expenditure
In the long term, can energy intake or expenditure be higher?
long term energy intake < energy expenditure
Are changes in body mass over time linear?
Rarely…
reducing energy intake by 500 kcal a day wouldn’t lead to 0.5 kg loss every week because as mass reduces, RMR and PAEE also decrease.
