Summary
The speed at which the body uses energy, affected by size, age, activity and hormones.
In depth
BMR is the energy at rest (about 1,500 to 1,800 kcal per day in adults). Affected by age, sex, body composition, thyroid hormone and temperature. Measured by oxygen consumption or heat output.
Metabolic rate is measured by direct calorimetry (heat) or indirect (oxygen use). Thyroid hormone raises it. Ectotherms have far lower rates than endotherms.
Example: shrews and hummingbirds have extremely high rates.
Metabolic rate is the amount of energy an organism uses per unit time. Basal metabolic rate (BMR) is the minimum at rest, awake, fasted and in a comfortable temperature, about 1,500 to 1,800 kcal per day for an adult.
It depends on body size, age, sex, muscle mass, hormones (thyroid hormones raise it), temperature and activity. Smaller animals have higher mass-specific rates; Kleiber's law shows rate scales with body mass to the power 0.75. Measurements use calorimetry (heat) or respirometry (oxygen use).
Example: a shrew eats almost constantly; an elephant much less per kilogram.
Frequently asked questions
What is Metabolic Rate?
The speed at which the body uses energy, affected by size, age, activity and hormones.
Which area of biology covers Metabolic Rate, and how advanced is it?
Metabolic Rate is one of the 53 topics in Metabolism & Bioenergetics. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Respiratory Quotient, Hormonal Control of Metabolism, Circadian Metabolism.
Why does Metabolic Rate matter?
It influences food needs, ageing and body weight.
Can you give an example of Metabolic Rate?
Muscle burns more energy at rest than fat.
What should I learn before Metabolic Rate?
Metabolic Rate is a Beginner topic, so no earlier topic is required. Other Beginner topics in Metabolism & Bioenergetics that pair well with it include Metabolism, Anabolism and Catabolism, ATP.
What topics are related to Metabolic Rate?
The closest topics to Metabolic Rate are Respiratory Quotient, Hormonal Control of Metabolism, Circadian Metabolism, Cori Cycle. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Metabolic Rate?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Metabolic Rate. To practise the whole of Metabolism & Bioenergetics, use the Metabolism & Bioenergetics quiz.
How is Metabolic Rate different from Respiratory Quotient?
Metabolic Rate: The speed at which the body uses energy, affected by size, age, activity and hormones. Respiratory Quotient: The ratio of carbon dioxide produced to oxygen consumed, indicating which fuel is being used. Read both side by side and note what each one explains.
How should I study Metabolic Rate step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Respiratory Quotient and explain the difference aloud. Finally, take the Metabolism & Bioenergetics quiz and come back to this page for any question you miss.