I'm male, 26 y/o, I run and bike regularly and think I'm in pretty
good aerobic shape.  But I never lift weights or do any exercise
involving my upper body (apart from occasional groceries).  Are there
any good health reasons to develop my upper body?  I'm satisfied with
my appearance now, and don't care about the cosmetic benefits of doing
it.

Hi! Thanks for the question.

The following links provide the benefits of weight lifting.


"Top Ten Reasons for Weight Lifting"
http://www.bodybuildingforyou.com/articles-submit/ghf/top-10-reason-weight-lifting.htm

"Benefits of Strength Training"
http://www.longfellowclubs.com/strengthtraining.htm

"Top 18 Benefits of Weight Training"
http://www.fitnessandfreebies.com/health/top18.html

"Weight training"
http://en.wikipedia.org/wiki/Weight_training

"Benefits of Weight Lifting'
http://ezinearticles.com/?Benefits-of-Weight-Lifting&id=286615

"Living Well: Weight-training brings benefits as you age"
http://seattlepi.nwsource.com/health/238207_condor29.html


Search terms used:
benefits of weight training lifting

I hope this would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
                                                          
                              
Regards,                              
Easterangel-ga                              
Google Answers Researcher

it would be useful to have a summary or a synthesis of the data, and
maybe an assessment of the credibility of these sources, instead of
just a bunch of links.  then again, $5 isn't very much to pay.

There are very good reasons NOT to do weight lifting.

Just look at the guys who've done it!

It's a great way to develop muscles that you don't need and these will
eventually turn to fat.

Ask yourself, 'Do I really want to be ugly?'

Of course, a six pack is better than a beer belly at the beach, but I
keep mine in a cooler.

Weight training might be more sensible.

Consider the amount of time you would need to put in to get any
measurable results.  With the right genetics you could look good with
two sessions a week, more frequent work-outs are required if you want
to be more buff or if you are unlucky enough to be a 'hardgainer'.

Consider the 'opportunity cost' of weight training and if there is
anything else you would rather be doing with your time.