Metabolic Rates and Factors Affecting Them

Basal Metabolic Rate

• the minimal energy conversion needed for daily basic life  functions including growth and repair of cells, nervous activity, breathing and heart rate, temperature regulation

When is BMR measured

• fasted

• rested

• thermoneutral state

Factors affecting BMR 

• age

• mass

• sex

• state of health of individual 

• body surface area to volume ratio

• hormones

• body composition

• genetics

Age

• BMR decreases with age

• babies have a higher bmr because it is needed for growth and development

• further muscle mass decreases with increasing age

Sex

• males have a higher bmr due to increased muscle mass and lower body fat percentage

State of health of the individual 

• fever/illness can increase BMR as the body needs more energy for the immune system and tissue repair

• malnutrition/severe illness lowers BMR as muscle mass decreases and slowed metabolism 

Surface area to volume ratio

larger surface area : volume ratio means loosing more heat - larger/rounder bodies loose less heat therefore have a lower BMR

Mass 

• larger mass = larger BMR

Hormones

• thyroxine → maintains a steady BMR rate increasing cardiac output, heart rate, breakdown of glucose, no. and size of mitochondria and rate of respiration (By increasing uptake of oxygen)  

• Adrenaline → rapid increase in metabolic rate during times of stress/danger

• Glucocorticoids → raises metabolic rate gradually during times of prolonged stress

• Insulin → energy storage, lowers or maintains bmr under resting conditions

Body Composition 

percentage of muscles - the higher the BMR

Genetics

• genes affect enzymes, hormones, muscle mass etc

• genetic conditions such as hypothyroidism