Market Data 
As a multi-sport athlete, I track my fitness through swim time trials, burnout lifts, and functional threshold power evaluations that push me to my mental and physical limit.
Bryan Johnson, the 48-year-old entrepreneur obsessed with longevity, has a much simpler and less grueling test as a proxy for how your body is aging, which may or may not match your chronological age.
Johnson led the exercise at Business Insider’s The Long Play event in San Francisco on Tuesday. You can do it anywhere with a timer.
The test: Start your timer, close your eyes, and stand on one leg. See how long you can avoid falling.
According to Johnson, if you stand for zero to seven seconds, your body is 60-80 years old. Seven to 15 seconds is 40-60 years old, and 15 to 30 seconds is 20 to 40.
“As you age, your brain atrophies, and your ability to maintain your balance goes away. That’s why when you get older, if you fall down, it’s no good,” Johnson said.
A small Mayo Clinic study of adults over 50 published in 2024 found that among several functional tests, one-leg balance time was most affected by age.
The Mayo Clinic researchers dubbed the one-legged test “a valid measure of frailty, independence, and fall status.”
Unlike Johnson’s version on Tuesday night, the study didn’t test people under 50, nor did it offer specifics about balance time matching biological age.
The balance test isn’t a new idea, and the Cleveland Clinic cautions that “it’s not a complete balance evaluation on its own” and it’s “far from a perfect indication of longevity.”
But by Johnson’s standards, my biological age — especially on my dominant, more stable left leg — is right where I should be.
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