Although it’s not easy to look at this without thinking about the Dirtbag Gourmet guide to cannibalism, these cross-section images of the thighs of three men are highly motivating. People of a certain age will acknowledge that kicking hard for another interval, adding another loop to your trail run, or banging off another skin lap gets progressively harder as you get older. We know both intuitively and empirically that it pays off, of course, but here’s even more evidence.

The first image shows the legs of a 40-year-old triathlete. The center oval is the femur, which is surrounded by muscle (dark) and then fat and skin (white). The second image is a 74-year-old sedentary dude (obviously, cause it’s labeled as such), which, no offense to our volunteer lab specimen, is appalling. The adipose tissue constitutes a huge percentage of the leg and the muscle is shriveled and unhealthy looking. No doubt this is a more common condition than not at age 74, but still – I don’t want the inside of my pins looking like that, do you?

But there’s hope, and this is the coolest thing of all. Look at the quads of our 70-year-old triathlete. They’re not so different from the 40-year-old, and while you can’t draw conclusions about longevity or health or PRs in the Ironman based on this image, Door #3 looks a whole lot better than Door #2 any day.

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Sweat Science, as usual, has an excellent take on this, along with plenty of well-informed comments. Worth a visit if you want to learn more.