Assessment of Energy Expenditure Flashcards

Total Energy Expenditure (TEE) is comprised of three primary components, each contributing a specific percentage to the daily total:
- Basal Metabolic Rate (BMR): Represents the largest component, accounting for approximately $65-75\%$ of daily energy expenditure. It is dictated largely by body mass.
- Physical Activity: Accounts for approximately $15-30\%$ of daily energy expenditure. This is the most variable component.
- Diet-Induced Thermogenesis (DIT) / Thermic Effect of Food (TEF): Represents approximately $10\%$ of daily energy expenditure. This is the energy required for the digestion, absorption, and storage of food.
Standardized Units for Energy Assessment:
- Kilocalories: $kcal$
- Kilojoules: $kJ$ . The conversion formula is $\text{kcal} \times 4.2$ .
- Megajoules: $MJ$ . The conversion formula is $\text{kcal} / 239$ (rounded).

Definition and Mechanism: Direct calorimetry measures the amount of heat produced by a subject while they are positioned inside a metabolic chamber or a whole-body calorimeter. It relies on monitoring temperature changes (e.g., $DTEMP$ ) in air or water circulating within the chamber walls to quantify energy expenditure based on heat loss.
Historical Context: Reference is made to the Atwater whole-body calorimeter as a historical standard in measuring energy output.
Limitations in Exercise Physiology: From the perspective of exercise physiology, direct calorimetry presents several significant problems:
- Inability to monitor rapid changes: It is not responsive enough to track quick fluctuations in metabolic rate during varied exercise intensities.
- External Heat Contribution: The friction developed by an ergometer used inside the chamber would contribute to the total heat produced, confounding the measurement of the subject’s own metabolic heat.
- Delayed Heat Liberation: Not all heat produced during physical exertion is immediately liberated from the body; heat may be stored in the core, making real-time measurement difficult.
- Lack of Substrate Specificity: It cannot determine which fuel (carbohydrates or fats) is being utilized at any given time. It only determines the overall metabolic rate.
Conclusion on Clinical Use: Direct calorimetry is deemed not suitable for use during acute exercise.

Mechanism: Indirect calorimetry estimates energy expenditure by measuring gas exchange (oxygen uptake and carbon dioxide production).
Key Techniques:
- Douglas Bag Technique: A method for collecting expired air to analyze volume and gas concentrations ( $O_2$ and $CO_2$ ) over a specific time period.
- Exercise Oxygen Uptake: Measured in $l/min$ . During Steady State Exercise, energy expenditure can be estimated using the ratio of oxygen consumed ( $VO_2$ ) to carbon dioxide produced ( $VCO_2$ ).

Predictive Factors: BMR can be predicted with reasonable accuracy using demographic and anthropometric data, specifically:
- Age
- Height
- Weight/Body Mass
The Schofield Equation: A standard formula used to estimate BMR in $kcal$ per day based on those factors.
Evidence and Accuracy: The accuracy of predicted BMR is supported by studies such as Johnstone et al. (2006), published in the European Journal of Clinical Nutrition ( $60\text{: } 1437-1444$ ).

Task 1: BMR Estimation:
- Estimate personal BMR using the Schofield Equation in $kcal/day$ .
- Ensure the conversion of units from $MJ$ back to $kcal$ where necessary.
Task 2: Comparison Analysis:
- Estimate how BMR would change if the subject maintained the same mass but was aged $30-60$ years or was of the opposite sex.
Task 3: Conversion to Active Rates:
- Calculate BMR in units of $kcal/minute$ .
- Calculate energy expenditure for exercise performed at an intensity equivalent to a $4.5\text{-fold}$ increase above BMR.

Metabolic Equivalents (METs):
- $1\,MET = BMR$
- $4.5\,METs$ represents the middle of the intensity range recommended for adults by the UK Government.
Application Example:
- For a $60\,kg$ , $20\text{-year-old}$ woman:
  - BMR = $1376\,kcal/d$
  - Exercising for $30\text{ minutes}$ at an intensity of $4.5\,METs$ results in a caloric burn of approximately $129\,kcal$ .
  - This amount is roughly $8-9\%$ of Total Energy Expenditure (TEE).
Duration Requirement: Calculate how long one would need to exercise at $4.5\,METs$ for the exercise-specific energy expenditure to equal the total daily BMR.

Exercise vs. Daily Life:
- Structured exercise typically accounts for only $2-3\text{ hours}$ per week.
- Movement Opportunity: Refers to the remaining time available for physical activity during waking hours, estimated at approximately $112\text{ waking hours}$ per week.
Future Planning: Further assessment of energy expenditure away from laboratory settings (free-living conditions) is scheduled for subsequent discussion.