Past Papers · SAQ
Basal Metabolic Rate
2023A Q07
Exam questionDefine basal metabolic rate and outline the factors that affect it (60% of marks). Outline the ways it may be measured (40% of Marks).
CICMWrecks answer
Master answer
Basal Metabolic Rate
- Energy expenditure required to maintain the body’s basic homeostatic mechanisms
- Normal BMR = 40kcal/m2/hr or approx. 70kcal/hr for 70kg male
- Relative organ contribution to BMR
- Liver 30%
- Brain 20%
- Muscle 20%
- Kidney 10%
- Heart 10%
- Other 10%
Factors that affect BMR
- Prandial effects
- Metabolic rate increases post-prandially for the digestion and absorption of nutrients
- After prolonged fasting metabolic rate decreases
- Thermoregulatory effects
- Temperatures above and below the thermoneutral zone cause metabolic rate to increase to support extra thermoregulatory mechanisms
- Response to heat
- Sweating
- Vasodilatation
- Response to cold
- Shivering
- Non-shivering thermogenesis
- Vasoconstriction
- Response to heat
- Temperatures above and below the thermoneutral zone cause metabolic rate to increase to support extra thermoregulatory mechanisms
- Physical activity
- Increased muscle activity
- Exercise increases metabolic rate in order to supply ATP to sarcomeres for contraction
- Increased muscle activity
- Inflammation
- Metabolic rate increases
- Chemotaxis
- Increased oxidative bursts
- Cell proliferation and clonal expansion
- Metabolic rate increases
- Psychological stress
- Hormonal factors
- Thyroid hormones → increase metabolic rate
- Maximal thyroid hormone activity increases MR 100%
- Thyroidectomy decreases MR 50%
- Catecholamines → increase metabolic rate
- Growth hormones → increase metabolic rate ~15~20%
- Testosterone → increase metabolic rate ~10~15%
- Thyroid hormones → increase metabolic rate
- Age
- Decreases with age >20
- Sex
- Male BMR > Female BMR possibly due to testosterone effect
- Body mass
- Muscle mass accounts for significant proportion of BMR, therefore increases BMR
- Sleep
- Decreases BMR 10~20%
Measurement of BMR
- Direct Calorimetry
- Atwater Chamber
- Subject placed in insulated chamber surrounded by H2O
- Change in temperature of water proprotional to metabolic rate
- Atwater Chamber
- Indirect calorimetry
- Metabolic carts
- Measurement of O2 consumption (and CO2, Urea production) to determine Metabolic rate
- Respiratory quotient
- Carbohydrates = 1
- Fats = 0.7
- Proteins = 0.8
- Metabolic carts
Conditions required to measure BMR
- Thermoneutral zone
- Free from psychological or physical stimulus
- After a night of restful sleep
- 12 hours after last meal
- 2 hours after last exercise
Sakurai 2016
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2023A Q07 | Define basal metabolic rate and outline the factors that affect it (60% of marks). Outline the ways it may be measured (40% of Marks). | 64% |
| 2013B Q09 | Define basal metabolic rate and list the factors that affect it. (60% of marks) Describe the ways it may be measured. (40% of marks) | — |
| 2008B Q04 | Define basal metabolic rate and describe factors that influence it (70% of marks). How could you measure metabolic rate? (30% of marks) | — |