A 47-year study reveals the age when your body starts losing strength
A 47-year study has uncovered a surprising turning point in physical aging: fitness and strength begin declining around age 35, even among people who exercise regularly. Researchers found that this decline accelerates as people get older, but starting to exercise in adulthood can still improve physical performance.
Key points
- A 47-year Swedish study of 427 people born in 1958 found that aerobic fitness and muscular endurance peak between ages 26 and 36 and begin declining around age 35.
- By age 63, average physical performance had dropped by roughly 30 to 48 percent from peak levels, with similar patterns in men and women.
- Becoming active in adulthood improved physical capacity by about 5 to 10 percent, though exercise could not completely stop age-related decline.
A 47-year Swedish study has found that physical abilities such as fitness, muscle endurance and overall performance begin to decline around age 35, even in people who stay active. Researchers at Karolinska Institutet tracked 427 randomly selected men and women born in 1958, assessing them from age 16 through age 63.
The findings, published in 2025 in the Journal of Cachexia, Sarcopenia and Muscle, show that aerobic fitness and muscular endurance peaked between ages 26 and 36. By age 63, average performance had fallen by roughly 30 to 48 percent from those peak levels, with similar rates of decline in both sexes.
What the study found
The research was part of the Swedish Physical Activity and Fitness study. Unlike most earlier research that compared people of different ages at one time, this project repeatedly examined the same individuals as they aged. Assessments covered aerobic fitness, muscular endurance and muscle power, which is the ability to produce force quickly.
Decline was initially modest but became faster with age. Even participants who remained physically active showed diminishing performance. However, those who became active in adulthood improved their physical capacity by about 5 to 10 percent, and those active in adolescence tended to maintain better fitness, endurance and muscle power.
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.
— Maria Westerståhl, lecturer at the Department of Laboratory Medicine and lead author of the study
Follow-up research and next steps
A 2026 follow-up study in Scientific Reports using the same group found that better aerobic fitness at ages 34 and 52 was linked to less arterial stiffness at age 63, even after accounting for obesity, smoking and blood pressure. The results do not prove that fitness directly prevented arterial stiffening.
Other 2026 studies cited in the article found that older adults who kept cycling over nine years had an average 19.7 percent decline in peak aerobic capacity but still performed at or above the 90th percentile for their age. A separate four-year study of 49 men ages 60 to 82 found that weekly resistance exercise improved strength. The Swedish research will continue with assessments at age 68.
