Guy Hoelzer  wrote or quoted:

> You may be interested in the following observation (I would point you to the
> literature on the metabolic scaling theory of Brown, West and colleagues).
> Data spanning many orders of magnitude in animal size and metabolic rate
> reveal that vertebrates are generally allotted about 1 million heart beats
> per lifetime.  There is plenty of variation around this rule, but the more
> data you include in the analysis, the more robust the rule appears. [...]

This is "between-species" data.

> So, when you work out you use up your allotment of heart beats faster, 
> but you reduce your resting heart rate at the same time.  You don't get 
> a larger allotment of heart beats by virtue of working out.

....and this is "within-species" data.

Using data on the former to make arguments about the latter doesn't
work very well - since for one thing all the data [1,2,3,4,5] indicates 
that vigorous exercise increases mean lifespan.

> There is one result from the science of aging that shows up in virtually
> every study.  The most effective way to maximize lifespan is to reduce
> metabolic rate.  You can increase your expected lifespan by something like
> 30%, for example, if you lie down, get fed intravenously, and allow your
> muscles to atrophy for the rest of your life.  It is not a life I would
> choose to live, but it is BY FAR the surest way to maximize your lifespan
> that we know.

The best known and most effective intervention for extending the lifespan 
of mammals (or practically anything else) is calorie restriction - i.e. see:

  http://calorierestriction.org/

It doesn't work by changing the organism's metabolic rate - but rather by 
activating adaptations for dealing with famine conditions - i.e. see:

  http://cr.timtyler.org/why/

> I would also argue that, whether or not there are other effective ways 
> of maximizing lifespan that we have yet to discover, the existing data 
> are clear with regard to the effect of metabolic rate.

If anything, it shows that it is pretty useless as a guide to lifespan
*within* species.

There are too many complications.  For example, increasing your 
metabolic rate using cold-stress creates mitochondrial membrane 
uncoupling, prevents the membrane potential ripping bits off
adjacent molecules, and - if anything - retards aging.

[1]
``Exercise intensity and longevity in men. The Harvard Alumni 
  Health Study''

 - http://calorierestriction.org/pmid/?n=7707624

[2]
``Associations of light, moderate, and vigorous intensity 
  physical activity with longevity. The Harvard Alumni Health Study''

 - http://calorierestriction.org/pmid/?n=10670554

[3]
``Physical activity and coronary heart disease in men: The 
  Harvard Alumni Health Study''

 - http://calorierestriction.org/pmid/?n=10961960

[4]
``Physical activity, physical fitness, and risk of dying''

 - http://calorierestriction.org/pmid/?n=10961960

[5]
``Physical activity and stroke incidence: the Harvard Alumni 
  Health Study''

 - http://calorierestriction.org/pmid/?n=10961960
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