Energy Expenditure (S1) Flashcards
(37 cards)
What are calories?
A unit of heat - amount of energy required to heat 1 gram of water by 1 degree
How can we estimate EE?
Direct calorimetry and Indirect Calorimetry
How do we estimate EE by direct calorimetry
40% of energy liberated from phosphate groups goes to fuel energy and the other 60% is lost as heat
- Therefore we can measure the amount of heat lost to the environment and make assumptions about how many calories being oxidised
- Heat inside the room heats the water surrounding the room and temp change is recorded
What are the pros and cons of direct calorimetry?
Pros - direct measure of heat (as calories are a measure of heat), accurate for steady state measure
Cons - expensive, slow to generate results (can’t see what’s happening at onset of exercise), few in operation, accurate for exercise? (equipment may generate heat)
What is indirect calorimetry?
measured via expired gases - conc of oxygen and carbon dioxide and how they change from air breathed in to air breathed out (respiratory exchange ratio - RER)
- it gives us an indiciation of substrate being used (carbs / fats)
Explain how indirect calorimetry relates to respiratory exchange ratio (RER)
RER for 1 molecule of glucose = 1.0
- consume 6 molecules of oxygen and produce 6 molecules of carbon dioxide
RER for 1 molecule of palmitic acid = 0.70
- 23 molecules of oxygen consumed to produce 16 molecules of carbon dioxide
- palmitic acid is a common saturated fatty acid we would usually be oxidising
What RER do we tend to have when working aerobically?
When working aerobically…have an RER of 0.7-1.0 (this predicts substrate use, kilocalories / O2 efficiency)
What are the benefits of indirect calorimetry? [5]
- Can detect changes during exercise with breath-by-breath systems
- No longer affected by heat of equipment (measure of pulmonary gas exchange only)
- Easy to administer
- Fairly accurate for aerobic measures
- Direct assessments of gas exchange
What are the limitations to indirect calorimetry? [3]
- Assumes the body’s O2 content is constant + CO2 exchange in lung is proportional to release from cells
- but CO2 released in lungs may not be representative of CO2 released by working cells
- and body has O2 stores not directly reflected in pulmonary measures
- Assumes little contribution from protein during exercise (but protein contributes up to 5% of total energy in prolonged exercise)
- Not suitable for anaerobic exercise due to extra CO2 produced due to buffering
Why can RER values >1 not provide a valid estimation of EE?
Due to carbon dioxide being producing via buffering
- even values approaching 1 can be inaccurate (as we’re becoming more anaerobic)
Why is RER not appropriate for EE estimation outside range of 0.7-1
Gluconeogenesis from catabolism of fat and amino acids can drag RER below 0.7
- creating new molecules of glucose (when breakdown fats -> glycerol molecule and 3 fatty acids in which glycerol can be strung together to make glucose)
What substrate gives us the most energy per gram?
Fats - 9kcal / g
What susbtrate costs the most oxygen per kilocalorie?
Fats - 4.69 kcal / L O2
At an RER of 0.71 - 100% of kcal from fats and 4.69 kcal / L O2
At an RER of 1.0 - 100% of kcal from carbs and 5.05 kcal/L O2
What’s the general rule for the kcal / L O2 consumed
5 kcal/L O2
Consuming a meal of 1164 kcal, how long would running at a VO2 of 2L/min take to ‘burn off’ this meal?
5 kcal/L O2 x 2 L/min = 10kcal/min
1164 kcal / 10 kcal/min = 116.4mins
Measuring time taken to burn off meal this way isn’t fully accurate however - why?
talking about using L / O2 and dividing oxygen consumed by this
It’s thinking about it directly - energy would be used to stay alive etc
What’s a government intervention that could be put in place to get people thinking about PA more often regarding food intake?
Rather than having a ‘traffic light system’ for salt, fat etc - should say need to ‘walk for 30mins’ to burn meal off
Why measure energy expenditure?
Most of it is to do with understanding how fuel is utilised and demands of exercising
- assess metabolic needs, fuel utilisation, nutritional interventions for performance / recovery, gaining insight into demands of training
Thermic effects of food - amount of energy it costs us to digest the food
Assessment of economy - if we can measure EE at a given intensity then we can implement interventions to improve economy and then measure EE again (should decrease)
What is basal metabolic rate? How does it compare to resting metabolic rate
BMR - ‘Pure’ resting energy expenditure
RMR - poorer measure hinting at same thing
How can BMR be measured in a lab?
Participant comes into lab completely rested - no activation of sympathetic nervous system + no TEF and have to stay in for period of time lying down
- usually first thing in morning
What’s the trend observed with BMR and ageing?
A 2-3% decrease in metabolic rate per decade
Why is the trend observed with BMR and ageing?
- Decrease in fat-free mass - as we age, tend to have less lean muscle mass (less PA)
- Depression of metabolic activity of lean tissues - possibly linked to PA and lifestyle change
- Change in body composition - could plateau instead of 2-3% decrease via resistance training to increase FFM
- Change in PA - independent of change in body comp
Why is RMR worse than BMR
Less tightly controlled than BMR + it’s not absolute baseline as participants are only really rested for 30mins or so
- but can be more accessible / applicable (less time-consuming + easier)
What are MET values?
Metabolic equivalents - essentially they are multiples of RMR
- where 1 MET = 3.5 ml/kg/min (energy expended when resting)
