Re: Physical fitness and evolution

From: Peter Webb (webbfamily_at_DIESPAMDIEoptusnet.com.au)
Date: 06/23/04 

Date: Wed, 23 Jun 2004 16:06:37 +0000 (UTC)

"Tim Tyler" <tim@tt1lock.org> wrote in message
news:cba42s$1f4a$1@darwin.ediacara.org...
> Peter Webb <webbfamily@diespamdieoptusnet.com.au> wrote or quoted:
>
> > People who exercise at the gym primarily do so for one of two reasons -
to
> > build muscle mass or improve cardio fitness.
> >
> > Its easy to see why the body only puts on muscle in response to weight
> > training. If there is excess food available, your body is better storing
> > this as fat rather than as muscle, as fat provides 9 kCal of energy per
Gram
> > you carry around, whereas muscle (protein) provides only 4 KCal/gm.
Carrying
> > fat around is more energy efficient than carrying muscle, unless you
have
> > some other need for the muscle. Weight training simply tricks your body
into
> > thinking you need muscle for other purposes, so it alters the balance
> > towards the less efficient storing of food as muscle.
> >
> > The adaptations that occur in response to cardio training are harder to
> > explain. These include increased capillaries, more mitochondria, and
> > numerous others. However, none of these seem to have a downside.
>
> They all have energetic costs to maintain. If you are not using muscles,
> they are probably not needed. Maintining them would be a significant
> energy drain. That's basically why muscles that are not used eventually
> atrophy.

Yes, the argument as to why muscles atrophy is clear, and I used it as an
example myself above (the energy cost involved in carrying around muscle is
higher than the energy cost in carrying fat, per gram of energy stored).

But what are the energetic costs of being fit in a cardio sense? Certainly
people who exercise use more energy, but not because they are fit per se;
its because they are exercising. I have never heard any suggestion that at a
given level of energy expenditure (eg walking 10 kms in two hours) that a
(cardio) fit person uses more calories than an unfit person - indeed, my
personal experience is quite the opposite.

I stress again that I am talking about cardio fitness. I understand that a
person with huge muscles will use more energy walking 10 kms in 2 hours than
somebody with normal build.

Given all of the health costs associated with being unfit - as well as the
considerable evolutionary disadavantage of not being able to run away from
sabre toothed tigers - I cannot see the corresponding benefit in your body
reversing the adaptations to exercise and becoming unfit.

>
> > Anybody know why not exercising makes you unfit, or has a plausible
theory?
>
> Tissues that are not used represent a drain in terms of the enegry
> needed to heat them - and the cost of lugging them around with you
> wherever you go. Also the more tissue blood has to flow through the
> harder the heart has to work.

But being cardio fit doesn't involve an increase in tissue.

>
> Calories were not readily available to most of our ancestors - they
> took care to conserve the ones they had, and avoided wasting them on
> unused functions.
> --

Yes, but I don't see that the adaptations that occur in response to cardio
training involve any additional energy consumption. (Though the training
itself obviously does). Its not tissue mass - cardio training doesn't
increase your body weight (usually the opposite). Nor have I have ever heard
a theory that fit people need more food than unfit people at the same level
of activity.

So what is the evolutionary advantage of reversing the adaptations to
exercise, which compensates for the huge disadvantage that unfit people have
when confronted by hungry tigers? What is the hidden (to me) cost of being
fit?

Relevant Pages

  • Re: How much weight are you really carrying?
    ... Balance is not what takes the bulk of the energy. ... and thus cannot be distinguished other than as muscle inefficiency. ... metabolic cost of walking. ... Although these factors explained less of the increase in metabolic rate ...
    (uk.rec.walking)
  • Re: Need Muscle Definition Quick
    ... cardio every day and HIT workouts M-W-F. ... while retaining most of the muscle. ... If you have only a week, HIIT will lose more fat than weightlifting. ... "HIIT (that's high intensity interval training, ...
    (misc.fitness.weights)
  • Re: How much exercise do you do?
    ... My plan was to run for 15 minutes after lifting on Mon-Wed-Fri on top ... > is impossible to both gain muscle and lose bodyfat. ... > gain muscle with all that cardio. ... I do 15 lifts (actually, ...
    (alt.support.diabetes)
  • Re: Physical fitness and evolution
    ... >> build muscle mass or improve cardio fitness. ... >> to exercise when the exercise stops? ... > because physical fitness and Darwinian fitness are very different things. ...
    (sci.bio.evolution)
  • Re: Need Muscle Definition Quick
    ... cardio every day and HIT workouts M-W-F. ... while retaining most of the muscle. ... If you have only a week, HIIT will lose more fat than weightlifting. ... "HIIT (that's high intensity interval training, ...
    (misc.fitness.weights)