Longevity clinics are booming. Prestigious hospitals want in.

CHICAGO — I was walking briskly on a steep treadmill, wearing a mask that evoked the villain Bane from “Batman.” Prince crooned back-handed compliments over an iPad speaker to keep my energy up, promising I had to be neither rich nor cool to be his girl. Every so often, the woman standing next to me asked me to point at the color-coded sheet ranking my state of exertion from 1 (roughly, “I could do this all day”) to 10 (“I not only hate this but am about to keel over if you don’t slow this thing down”). The goal was to get to 10. Pushing myself to achieve difficult physical goals does not come naturally. I can’t go on, I thought. I went on.

This was the VO2 Max test, which shows how efficiently the body uses oxygen (“V” stands for volume, “O2” for oxygen) and is considered medicine’s most accurate measure of cardiorespiratory fitness. It was the last in a barrage of assessments I’d undertaken at a shiny longevity clinic affiliated with Northwestern University — part of a $5,500 annual package.

The quest to defeat the indignities of aging has long provoked costly and questionable practices, from the 1920s doctors who believed in the rejuvenating power of grafted monkey testicles to Bryan Johnson’s since-abandoned blood transfusions from his teenage son. Now some of the nation’s most prestigious health systems are jumping into the growing business of longevity. They promise a rigorous scientific approach to helping people preserve their youthful vigor for as long as they can, with assessments that give patients more detailed pictures of their current physical conditions and aging trajectories than they’d get at a typical doctor’s visit.

Some critics, however, question how to reconcile the clinics’ high out-of-pocket costs with hospitals’ nonprofit status and charitable missions, and warn that in their zeal to attract paying customers, they’re offering tests that lack sufficient evidence showing they actually improve people’s health.

STAT+ Exclusive Story