Physical decline: A decades-long Swedish study tracking the same adults for nearly half a century has found that physical capacity typically peaks around age 35 and then begins a gradual decline that accelerates later in life, while also showing that people who start exercising in adulthood can still make measurable gains.
Researchers at Karolinska Institutet followed several hundred randomly selected men and women in Sweden, repeatedly testing fitness, strength and muscle endurance as participants aged from 16 to 63. The work is part of the Swedish Physical Activity and Fitness study (SPAF) and was published in the Journal of Cachexia, Sarcopenia and Muscle.
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Unlike many earlier studies that compared different age groups at a single point in time, the Swedish project repeatedly measured the same individuals over 47 years, offering a long view of how performance shifts across adulthood.
The results showed that fitness and strength began to fall from around age 35, regardless of how much participants had trained earlier. From there, performance declined steadily and tended to worsen with advancing age.
The study also delivered a more encouraging takeaway: participants who became physically active later in adulthood improved their physical capacity by about 5% to 10%, suggesting that meaningful progress is still possible even after peak years have passed.
Lead author Maria Westerståhl said the findings support staying active across the lifespan, even if exercise cannot fully stop age-related decline. The researchers plan to continue tracking the group, with the next round of testing scheduled when participants reach age 68, to better understand how lifestyle, health and underlying biology shape long-term changes in physical performance.