A review in Geriatrics proposes defining aging as a loss of self-correction, the body's ability to respond to a challenge and recover, and measuring it through recovery after exertion
A review in Geriatrics proposes defining aging as a loss of self-correction, the body's ability to respond to a challenge and recover, and measuring it through recovery after exertion
On September 16, 2026, David Bar-Or and Jason Williams of Swedish Medical Center and Daniel Paredes of the University of Denver published a review. The hallmarks of aging that Carlos López-Otín and colleagues outlined in 2013 describe what changes: DNA becomes damaged, and senescent cells accumulate. The review's authors propose a cycle of self-correction to explain how these changes impair the body's ability to cope with challenges.
The cycle has five steps: the body detects a significant challenge (an injury or infection), scales its response to that challenge, repairs the damage, ends the response, and recovers or reaches a new equilibrium while retaining functional reserve for the next challenge.
The authors consider the step of ending the response underappreciated: research more often examines how inflammation starts than how it stops. Lipid signaling molecules help resolve inflammation, and the authors suggest that aging tissues become less able to switch from molecules that sustain inflammation to those that resolve it. In their view, someone with a strong inflammatory response that resolves effectively may be biologically younger than someone with a mild but prolonged response. In old age, tissue repair often shifts toward scarring and calcium deposition. “Longevity requires the ability to complete repair,” the authors write.
The body keeps many variables, such as body temperature, near a set point. The authors suggest that, with age, this set point may shift toward a harmful state, such as chronic inflammation, which the body then works to maintain.
“A rapid return to an already pathological set point does not indicate healthy recovery.”
The authors therefore propose comparing the state after a challenge against three reference points: the person's own state before the challenge, the norm for their age and medical conditions, and a youthful state. They predict that two people with identical measurements at rest may recover differently. They propose measuring this difference after an exercise stress test, vaccination, or elective surgery: how far a measure (such as walking speed) deviates from the reference point, how long it takes to recover halfway, and how much of a deficit remains at a specified time.
The review draws its approach to measuring recovery from geriatric medicine, where physical resilience means the ability to maintain function after illness or surgery or to regain lost function. In the Baltimore Longitudinal Study of Aging, MRI shows how quickly muscle mitochondria replenish energy stores after exertion, with faster replenishment associated with a lower risk of cognitive impairment. Slower recovery with age can also be seen without an exercise challenge: in 2021, Gero reported in Nature Communications that repeated blood tests showed a composite measure of the body's condition returning to its usual level in about two weeks in groups of 40-year-olds, compared with more than eight weeks in groups of 90-year-olds.
The authors expect recovery measures to predict recovery after surgery, disability, and death independently of age and some conventional measurements taken at rest. An intervention that improves the ability to adapt should improve these measures even when static “aging clocks” (estimates of biological age based, for example, on DNA marks) barely change. The authors acknowledge that the model would need to be revised or rejected if these measures add no predictive value beyond age and conventional measurements, or if the findings cannot be reproduced.