A 47-year Swedish study has found that fitness, strength, and muscle endurance begin to decline earlier than many people expect — starting around age 35. The positive takeaway is that starting exercise in adulthood can still improve physical ability and help slow this gradual decline.
Conducted by researchers at Karolinska Institutet, the study tracked participants over nearly five decades to understand how physical performance changes throughout adulthood. The research is part of the Swedish Physical Activity and Fitness study (SPAF) and provides rare long-term evidence rather than short-term comparisons.
A Unique 47-Year Look at Fitness Across Adulthood
The SPAF study followed several hundred randomly selected men and women aged 16 to 63 at the start of the research. Their fitness levels, muscle strength, and endurance were measured repeatedly over time, offering a detailed picture of how physical capacity evolves across adulthood.
Published in the Journal of Cachexia, Sarcopenia and Muscle, the findings stand out because most previous studies relied on cross-sectional data. Those studies compared different age groups at one moment in time, while this research followed the same individuals for 47 years, making it one of the most comprehensive studies of its kind.
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Physical Performance Declines After 35 — But Exercise Still Matters
The results show that fitness and strength begin to decrease around age 35, regardless of how active someone was earlier in life. After this point, physical performance continues to decline gradually, with the rate of decline increasing as people grow older.
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Despite this trend, the study delivers encouraging news. Participants who became physically active during adulthood were able to increase their physical capacity by 5 to 10 percent. This demonstrates that exercise remains beneficial even when started later in life.
“It is never too late to start moving. Our study shows that physical activity can slow the decline in performance, even if it cannot completely stop it,” says Maria Westerståhl, lecturer at the Department of Laboratory Medicine and lead author of the study.
Next Steps in the Ongoing Research
The study is still continuing. The research team plans to examine participants again next year when they reach age 68. This next phase aims to better understand how lifestyle factors, overall health, and biological processes are linked to changes in physical performance over time.
