One does not have to be strong or have great strength to live longer. My paternal grandfather was of a slight build, not particularly strong, and he lived to be 103. He was relatively lean, avoided alcoholic drink, ate more vegatables than meat, and ate very little red meat (beef), which may have been more the case in later life than early.
He did walk a lot, did some gardening, and remained active, but his activities were moderate and not heavy.
I am not sure if 'splitting fibers' is correct, or perhaps they divide, but certainly lifting heavy weights promotes muscle growth in conjunction with the hormone testosterone. Using muscles keeps them fit, and usually good fitness contributes to a long healthy life. Larger muscles enable one to lift more weight or exert more force. But notice that rock climbers are quite lean, so they maintain a low mass and therefore have a high strength to mass/weight ratio as opposed to being bulky.
Diet and genetics are certainly other key factors. Some persons, like my father, are predisposed to colon cancer. He just recently had surgery to remove a tumor, and had subsequent chemotherapy to mitigate micrometastisis. Had he had a check up several years ago, the polyp could have been removed before it developed into a tumor. Also, it's possible that a different diet (higher in fiber and berries, e.g. strawberries and blackberries, and lower in fat) might have helped mitigate the onset of polyps/tumors.
Exercise is also a good way to relieve stress, and some studies have shown that exercise can improve one's immune system. Exercise is also necessary for good cardiac efficiency.
http://www.clevelandclinic.org/health/health-info/docs/0900/0955.asp?index=5429
http://sportsmedicine.about.com/cs/exercisephysiology/a/aa100303a.htm
http://sportsmedicine.about.com/cs/injuryprevention/a/aa011502a.htm
http://www.wellnessletter.com/html/fw/fwLon16Immunity.html
If articles sound similar, they may be one source using another or multiple sources using the same original source.
However, in my own case, I need a certain amount of exercise, and occassionally I need to do some heavy or exertive exercise to feel right. For me, it's the equivalent of blowing carbon out of the cylinders in an IC.
I walk at least 2-3 miles everyday, and that's down and up a hill with a rise of about 300 feet elevation in about 8000 ft of distance.
