Energy Expenditure Flashcards
What is a calorie?
The amount of energy needed to raise one gram of water by 1 degree celcius
How does a calorimeter calculate the calories in food?
- Put a sample of the food in a ‘bomb cell’ surrounded by a water bath
- They oxidise (burn) the food sample and calculate the temperature change in the water due to this
What reasons do we need to measure energy expenditure?
- Assess metabolic needs
- Fuel utilisation
- Thermic effects of foods
- Nutritional interventions for performance and recovery
- Assessment of economy
How can we estimate EE?
Indirect Calorimetry
Expired air gas analysis, the amount of oxygen consumed and the amount of CO2 produced.
How can we do direct calorimetry with a human?
- Measure all the heat that’s given off by them during exercise
- The heat is picked up by the water system in the room and therefore can work out the change in temperature
What are the Pros and Cons of direct calorimetry?
Pros: Direct measure of heat & Accurate for steady state measures
Cons: Expensive, Slow to generate results, Few in operation & Accurate for exercise?
What is the Respiratory Exchange Ratio?
RER
Production of CO2 : Uptake of O2
What would an RER of 0.7 indicate?
Fat burning
What would an RER of 1.0 indicate?
Carbohydrate burning
What are the advantages of indirect calorimetry?
Gas analysis
- Can detect changes during exercise with breath by breath systems
- No longer affected by the heat of equipment
- Easy to administer
- Fairly accurate for aerobic measures
- Direct assessments of gas exchange
Which fuel substrate gives us the most energy per gram?
Fat, around 9 Kcal vs 4 Kcal for carbs
Which fuel substrate costs the most oxygen per kilocalorie?
Fat, about 5 Kcal per litre of oxygen consumed so we get slightly more energy per litre of oxygen from the carbohydrates
What are limitations of Indirect Calorimetry?
- Assumes the body’s O2 content is constant but the body has O2 stores that isn’t directly reflected in pulmonary measures
- CO2 exchange in the lungs is proportional to release from cells
What RER will someone reach at their VO2max?
1.15
What is Basal Metabolic Rate?
The energy cost for someone at rest
Why does BMR decrease 2-3% per decade?
- Decrease in fat free mass
- Depression of metabolic activity of lean tissues
- Altered by change in body composition and physical activity
What is the difference between BMR and RMR?
Resting Metabolic Rate
BMR is a less tightly controlled version and is more accessible
What does MET stand for?
Metabolic Equivalent of Task
What does MET tell us?
For each activity you carry out, how many multiples of RMR is that activity worth?
What is 1 MET equal to?
3.5ml/kg/min
How many MET are required for running at a moderate high pace (70% of VO2max) for a man whose VO2max is 60ml/kg/min?
0.7 x 60 = 42
42 / 3.5 = 12
Therefore this is a 12 MET activity
What is Fat Max?
A description of the intensity at which maximum rate of fat utilisation occurs
What benefit does having a higher Fat Max give us?
Allows us to increase the intensity we can go to before relying on carbohydrates as a fuel
What is Mechanical Efficiency?
External work accomplished / energy expenditure
