Define physical fitness.

[DSeid]

@Chief_Pedant

Body weight and longevity: It would be more precise to say that, on average, calorie restriction is more typically associated with longevity than calorie excess. And, as always, what we see is really governed by our genes as much as our nurturing. …

Not quite sure why you think those cites are meaningful answers to my question of “How thin?”

No question that there is an obesity problem in America and that being obese is both a risk factor for bad outcomes itself and a symptoms of inadequate physical activity and of poor nutritional choices, which are also independent risk factors whether or not you are obese.

And if by “thin” you mean “not obese” then sure. Thin usually means a lower than normal BMI though and even a low normal BMI has a worse mortality rate than a high normal to slightly overweight one. Oh, not by much, but “overweight” (BMI 25 to 29.9) was indeed slightly lower. And “thin”, if that means less than “normal” was a greater mortality risk than obese was at all age groups and for some even than was significantly obese (BMI over 35).

So a cult of “thin” may in fact be quite harmful.

As to the need for muscle. Here’s a website article review that actually cites some important studies aimed at cyclists. Aerobic aint enough.

“Sometimes athletes in their late 20s and early 30s will come in for a femur or a hip fracture, and they’ll be surprised because the fall was really not that bad,” says Dr. Max Testa, a sports medicine physician at the Orthopedic Specialty Hospital in Salt Lake City who routinely treats elite cyclists. “But we’ll look at the X-rays and see that there is some osteopenia [lower-than-normal bone density] there.”[1]

As it turns out, the primary culprit is a factor long considered a positive of cycling. It’s a low-impact sport that puts little mechanical load on the bones. That’s great if you have joint problems, but it’s the weight-bearing nature of exercise that stimulates bones to become denser. That’s why weightlifters have far denser and stronger bones than normal folk, while low bone mineral densities are often observed in swimmers and long distance runners[2-5].

I’ll speak only for myself. I am a 51 year old Jewish guy. My youngest is my 9 year old daughter. One of my fitness goals is that when she gets married in maybe 20 years, that I won’t only still be around to celebrate, but that she’ll feel confident in having me be one of the people lifting up her chair above our heads and dancing around, or maybe even her husband’s. If I am going to have enough strength and endurance to do that at 70 plus, then I’ve got to work on preserving or increasing it now. Moderate aerobic alone won’t be enough to have me be that obnoxious proud 70 year old father, embarrassing his daughter one more time.