[colarris (OP)]

I've never understand the meaning of 'being fit'. I realize someone may be able to run further than me but thats it. If someone is fitter than me what will be the physical differences? If we could look inside our two bodies how would they compare?

[CliffordK]

Certainly fitness is a continuum, from the "couch potatoes", to those that enjoy personal activities, to the elite athletes.

There may be many things you would notice.
Obviously there is strength and stamina that can be measured with things like weights, races, jumping, and etc.

Inside, one would note more muscle, less fat.
There is an element of "use it or loose it", and even some things like bone density may be related to impact exercise, although, obviously many athletes overstrain their bodies causing permanent injuries.

The heart may actually be more compact for the athletes.  Cardiomegaly is actually a bad condition.

I suppose I would encourage doing what feels comfortable, without over-emphasizing spending hours a day exercising, although many people find moderate exercise relaxing.

[colarris (OP)]

many thanks.

 What changes are there in the body when someones stamina is increased? Are they physical changes?

[Lmnre]

Fitness is simply "survival of the fittest" and depends on the parameters to measure survival.

• If people must run frequently, then runners are fit.
• If people must sit frequently, then sitters are fit.
• If the climate is hot, then skinny people are fit.
• If the climate is cold, then fat people are fit.
• If people must observe at distances, then far-sighted people are fit.
• If people must examine close up, then near-sighted people are fit.
• Etc.

I think what we've seen is that the criteria for survival has shifted from the physical to the social, mental and psychological, thus people's physical fitness has followed the change and has likewise been de-emphasized.

[Nizzle]

many thanks.

 What changes are there in the body when someones stamina is increased? Are they physical changes?

Yes:
- Your resting metabolism goes up, meaning that if you are fitter, you're even burning more calories while doing nothing. This is because the muscle cells require more "maintenance energy" than fat cells.
- Your heart rate will go down. I believe this has to do with the fact that  O₂ <-> CO₂ exchange in your lungs happens in a more efficient way (read: bigger surface) when you're fit. This allows your heart rate to slow down while maintaining the amount of O₂ transported throughout your body.
- Your bone density will increase, effectively slowing down any osteoporosis processes if they would be present, because you will put more stress on your skeleton by living an active life.
- Exercising releases endorphin, which make you happy and cause the 'runner's high' symptoms, giving you a generally better feeling about yourself.
- Your self perception will improve and you will gain some self respect and self confidence (might be physical changes in your brain

just be careful not to overdo it in the beginning and give your body some time to adjust if you're changing your life style.