There are two main ways
you can produce energy -
aerobically (with oxygen)
and anaerobically. When
you very first start
exercising, your muscle
cells make energy without
oxygen (anaerobic
respiration. And don't get
confused; that is cellular
respiration (which is how
cells make energy), not
respiration as in breathing
with your lungs). This
causes lactic acid to build
up (lactic acid in your
muscles causes cramps)
and you need oxygen to get
rid of it. So you start
breathing more heavily to
get more oxygen to start to
get rid of that lactic acid.
You also start breathing
more heavily so that you
can now use that oxygen to
produce energy in a way
that DOESN'T make lactic
acid (aerobic respiration)
As long as you aren't
exercising at your absolute
maximum level (such that
you are using ALL the
oxygen that you are
breathing in to produce
energy), eventually you will
be able to get rid of that
lactic acid that your cells
produced. At that point
there's no lactic acid to
make you feel like you need
to breath in extra oxygen to
get rid of it, so you only
need to breath in enough to
keep your cells respiring
aerobically. Usually you get
your second wind around
20 minutes or so.
If you exercise a lot you can
increase the amount of
oxygen that gets to your
cells when you are working
out (your VO2) and it doesn't
take as long to get rid of the
lactic acid you build up in
the first minute or so of
exercise (that is anaerobic),
I probably just confused you
a ton. Sorry. Probably a
general high school biology
textbook will explain it more
clearly - just look up the
chapter on respiration. It all
has to do with the Kreb's
cycle! :)
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ADF makes great sigpics!