What Jack LaLanne taught us about aging

Editor's note: Dr. Mark Lachs is professor of medicine at the Weill Medical College of Cornell University and director of geriatrics for the New York Presbyterian Health Care System. He is the author of "Treat Me, Not My Age: A Doctor's Guide for Getting the Best Health Care as You or A Loved One Gets Older" (Viking Penguin 2010).

(CNN) -- It was the 1950s, and we were getting fatter, lazier and puffing away on cigarettes (often as the coda to a meal filled with saturated fats). Then along comes this lone, indefatigable voice telling us -- with great kindness -- to cut it out.

I'm not exactly sure why Jack LaLanne's message resonated so well way back then. Maybe it was because he looked like your gym teacher but was way nicer. Maybe it was his "American" sensibility -- the can-do attitude, the upbeat affability, even his fun sense of entrepreneurism. Whatever the recipe, I would argue that every modern-day advance in exercise and nutrition is somehow derivative of this pioneer's work and vision.

But as an internist who specializes in geriatric medicine, I believe that one of the great values of LaLanne's later life and message is that he embodied many important attributes of healthy aging. LaLanne was a force of nature till his death on Sunday at 96.

Back when LaLanne began his TV exercise show, older adults with and without disabilities (which in that epoch, started around 50) were told by their doctors to slow down and stop exercising. Of course, he would have none of it.

Five decades later, hundreds of studies demonstrate the positive benefits of exercise and mobility on everything from depression to fall prevention. He was the original "use it or lose it" guy, correctly preaching to us that things in motion tend to stay in motion, and things (and people) that don't will stop, or worse.

LaLanne was essentially telling us to maintain what gerontologists call "physiologic reserve," making sure that the extra capacity we're given at birth is available to support our unprecedented longevity, which is a very recent development.

What else did LaLanne demonstrate? A sense of purpose and adaptive social integration.

The arc of the Jack LaLanne story was consistent over his lifetime; for him it was getting us fit. It gave his life meaning and purpose.

I see this repeatedly in my older patients -- one or two interests that continues to "turn their gears" as one of my 98-year-olds likes to say. It really doesn't matter what that "it" is as long as there's something.

And the adaptive social integration? While social networks shrink with aging for many, his seemed to grow as he transformed his message for a changing world.

Sure, his TV show in the 1950s was revolutionary, but so were his juicing infomercials and many of his other ventures that continued to connect us to him and vice versa. How many 96-year-olds do you know with a Facebook page? (Today, it features an avalanche of tributes from adoring fans.)

In an age of cynicism for celebrities, he was the rare exception who didn't seem to have a hypocritical bone (or muscle) in his body. He was the lifelong friend who, quite literally, "walked the walk" for nearly a century. An American original.

The opinions expressed in this commentary are solely those of Mark Lachs.