The Age Your Fitness Starts to Change—And Why It’s Not Too Late
Key Takeaways
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Researchers followed 427 Swedish adults from age 16 to 63, repeatedly measuring aerobic fitness, muscular endurance, and muscle power.
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Average aerobic fitness and muscular endurance were highest between ages 26 and 36; some measures of explosive power peaked earlier.
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Declines began gradually around the mid-30s and accelerated with age, with average performance 30% to 48% below peak levels by age 63.
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This is a population pattern—not a rule that an individual suddenly declines at age 35 or cannot become stronger afterward.
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Participants who became more physically active during adulthood improved physical capacity by roughly 5% to 10%.
Most studies compare people of different ages at a single moment. This one repeatedly tested the same group across nearly five decades, allowing researchers to observe how physical capacity changed as participants grew older.
The results showed a shared general trajectory: physical capabilities tended to reach their highest average levels in early adulthood, then decline slowly at first. But people varied widely, and remaining active was associated with better fitness, endurance, and power across adulthood.
Decline Is Not Destiny
The study offers a useful correction to two common assumptions. First, being active does not completely erase biological aging; even active people tended to see performance decline over time. Second, the benefits of movement do not disappear after the age when population averages peak.
People who increased their activity in adulthood improved their physical capacity, reinforcing that a personal baseline can still move upward even when the broader age-related curve trends downward.
Fitness May Echo Forward
In a follow-up analysis of the same cohort, people with better aerobic capacity in their 30s and early 50s tended to have less arterial stiffness at age 63. That association remained after researchers considered several established health factors, though it cannot prove that fitness itself caused the later difference.
Together, the studies point to a practical idea: training does not need to “stop aging” to be worthwhile. Preserving the strength, endurance, and aerobic capacity that make stairs, carrying groceries, travel, and everyday independence easier is a meaningful goal at any age.
References:
- Maria Westerståhl, Gustav Jörnåker, Eva Jansson, Ulrika Aasa, Michael Ingre, Kaveh Pourhamidi, Brun Ulfhake, Thomas Gustafsson. Rise and Fall of Physical Capacity in a General Population: A 47‐Year Longitudinal Study. Journal of Cachexia, Sarcopenia and Muscle, 2025; 16 (6) DOI: 10.1002/jcsm.70134