Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Medical How do you find out energy required per day?

  1. Aug 20, 2013 #1
    Human body needs about 2000-2500 calories per day. How do you find out this number?
    What sort of experiments do people do to figure out this number?

    Also, in general how do you find things like - energy spent while walking, talking, blinking? It almost seems impossible to find out these things but I find numbers in books.
     
  2. jcsd
  3. Aug 20, 2013 #2

    mfb

    User Avatar
    2015 Award

    Staff: Mentor

    Some things you can try:
    - measure the produced heat of the body during those activities (and at rest)
    - measure the required oxygen, as this is related to the consumed energy
    - measure the required food (long-term measurement)
    - use some model of the muscles to find an estimate
    - probably some concepts I forgot or do not know
     
  4. Aug 20, 2013 #3
    I find it extremely hard to believe that you can actually calculate energy we require for doing activities. There are just too many things involved. Does this actually work?
     
  5. Aug 20, 2013 #4

    mfb

    User Avatar
    2015 Award

    Staff: Mentor

    It is possible to find approximations. The actual power/energy will vary a bit between different persons, details of the activity and other circumstances. And you always have a measurement uncertainty, of course.
    It is just interesting how precise those values are. To find some values is easy.
     
  6. Aug 20, 2013 #5
    Just for the sake of an example, say I want to calculate energy it takes for an average man to climb 30 stairs (30 steps).
    I just calculated using E = m.g.h. Will that be a correct approximation? Why/why not?
     
  7. Aug 20, 2013 #6

    mfb

    User Avatar
    2015 Award

    Staff: Mentor

    It is a lower limit. The human body is far away from 100% efficient.
     
  8. Aug 20, 2013 #7

    Ryan_m_b

    User Avatar

    Staff: Mentor

    There will also be other complications like the fitness of the person in question. An unfit person will take longer to return to a basal (resting) metabolic state so in addition to the energy expended climbing the stairs there's the period after characterised by faster heart rate, heavy breathing etc.
     
  9. Aug 20, 2013 #8

    Borek

    User Avatar

    Staff: Mentor

    How is it different from measuring heat of any process? Technically you just use a larger calorimeter (think thermally isolated room). I believe that's how the early experiments were designed.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted
Similar Discussions: How do you find out energy required per day?
  1. How do you die in space? (Replies: 12)

Loading...