Re: Physical fitness and evolution

From: Guy Hoelzer (hoelzer_at_unr.edu)
Date: 06/24/04 

Date: Thu, 24 Jun 2004 04:29:23 +0000 (UTC)

Hi Emile,

in article cbc9qb$26u1$1@darwin.ediacara.org, Emile at emile27@hotmail.com
wrote on 6/23/04 9:06 AM:

> Guy Hoelzer wrote:
>> in article cb7rtc$mic$1@darwin.ediacara.org, Peter Webb at
>> webbfamily@DIESPAMDIEoptusnet.com.au wrote on 6/21/04 4:44 PM:
>>
>>
>>> 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. Being
>>> fitter in a cardio sense always seems better than being unfit (unlike the
>>> situation with muscle vs fat).
>>
>>
>> Actually, these adaptations generically result in a shorter lifespan. They
>> improve your performance in the meantime, but they also cause you to live
>> faster (metabolically) and senesce sooner.
>>
> This is not necessarily true; check out this recent nature report on a
> study (1) where mice with sped up metabolisms live longer:
>
> http://www.nature.com/nsu/040531/040531-2.html
>
> E
>
> 1: Speakman et al. (2004) Aging cell. 3(3):87

Thanks for the reference. Wayne Van Voorhies is actually an old grad school
friend of mine, so it was great to see his commentary on Speakman's results.
I personally think that there is rather overwhelming evidence, and strong
theoretical reasons, supporting my original statement. My first
interpretation of the Speakman result is that he found a mutant mouse in
which the metabolism of mitochondria is less constrained by the function of
the whole organism. Because mitochondria are so small they naturally tend
to have a higher metabolic rate than the cells in which they exist.
Speakman noted that these mitochondria produce much more heat and provide
LESS fuel to the cell than normal mitochondria. Therefore, I would say that
the metabolic rate of the mouse has actually decreased when you discount the
wasted heat production of the mitochondria, which would explain why these
mice live longer. I predict that the mitochondria of these mice have
shorter life spans than normal mitochondria, and that the general
physiological functioning of the mice and their cells would be compromised
by the degree of independence being expressed by their mitochondria.

Cheers,

Guy