A small NIH study used full-body 3D scans to find the body measurements that track chronological age most closely — and smaller thighs and calves turned out to be among the strongest signals. The researchers then linked a larger gap between that body-shape age and actual age to weaker physical function and faster decline in some measures of movement.[1]
What the researchers measured
Researchers from the National Institute on Aging scanned 302 volunteers (mean age 71.7, range 27 to 95; 58% women) in the long-running Baltimore Longitudinal Study of Aging with a 3D body scanner, capturing 171 separate anthropometric measurements per person — far more detail than the usual body mass index (BMI) or waist-to-height ratio. Using a machine-learning technique called LASSO regression, they identified 22 measurements that, together, predicted a person’s chronological age with real accuracy (average error: about 4.5 years).
The measurements most strongly linked to older age were lower thigh girth, waist-to-buttock length, and calf girth — smaller measurements in all three tracked with older age. (Waist-to-buttock length is a torso measure, which the authors tie to spinal shortening, not leg size.) The researchers call the gap between your “predicted” age from these measurements and your actual age the anthropometric age gap (AAG): a bigger gap means your body shape resembles that of an older person. The gap is, by construction, the model’s prediction error, and the model itself was only moderately accurate.
What the gap was linked to
A larger AAG was linked to more than appearance. People with a bigger gap between predicted and actual age scored lower on cognitive tests related to motor planning, had weaker physical function, and carried less lean mass in their lower body. Tracked over an average of 13 years (up to 20 years for some participants), a bigger AAG also predicted faster future decline in manual dexterity, balance, and eccentric muscle strength — the kind of controlled, lengthening muscle contraction you use walking downstairs or catching yourself from a stumble.
These are associations in 302 people. The authors call the analysis exploratory and say the underlying mechanisms are unknown, so the study does not show that thinning legs cause, or come before, these declines.
What this means for you
The study did not test any home measurement or training plan, so the following are our suggestions rather than study findings:
- Know what the study found about thigh and calf size. In a side analysis, lower thigh and calf girth were linked to slower walking and weaker knee strength over time, but not to balance or dexterity decline. The study did not test home tape measures. If your legs are getting noticeably thinner without a reason such as weight loss, mention it to a doctor, since illness and some medications can also cause it.
- Train legs directly, not just cardio. Squats, lunges, step-ups, and calf raises build lower-body lean mass, which this study linked to physical function. The study did not test training, so this is our suggestion.
- Add single-leg balance work. Balance is one of the measures a larger AAG was linked to, and simple balance drills (standing on one leg while brushing your teeth, for example) are a common suggestion; this study did not test them. Stand next to a counter you can hold if you feel unsteady.
Limitations: this was a small, exploratory study of healthy volunteers from a single cohort, mostly older adults, and the authors note the sample may have underestimated variation in the wider population. Findings in people in their 40s and 50s may differ.
References
- Tian Q, Shin S, Bustin K, et al. “Accelerated Anthropometric Ageing Links Loss of Physical Function and Lower Extremity Body Mass.” Journal of Cachexia, Sarcopenia and Muscle, 2026;17(4):e70367. Finding used: in 302 Baltimore Longitudinal Study of Aging participants, lower thigh girth, waist-to-buttock length, and calf girth were the strongest anthropometric predictors of chronological age, and a larger anthropometric age gap (AAG) predicted concurrent and future declines in cognitive motor planning, physical function, balance, manual dexterity, eccentric strength, and lower-extremity lean mass. DOI: 10.1002/jcsm.70367. Source: PubMed 42572387. ↑︎
Kurt Greiner
Kurt is a digital strategist and IT professional blending emerging technology with practical application to help businesses and individuals streamline their digital presence. His current work focuses on the intersection of intentional living and technological resilience, exploring how individuals can leverage modern tools to navigate the second half of life with purpose.
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