Most people associate aging with their 50s and beyond, but a new study shows physical capacity actually begins its slow decline in the mid-30s. Even without specific illnesses, fitness, muscle strength and muscular endurance start to deteriorate around age 35, with the pace of decline accelerating as people grow older.
According to the science publication ScienceDaily on the 15th (local time), a research team at Sweden's Karolinska Institute confirmed these findings in a paper recently published in the Journal of Cachexia, Sarcopenia and Muscle. "A decline in fitness comes to everyone, but the speed clearly differs depending on physical activity," the researchers said.
The study stands out because it tracked the same participants over several decades, unlike previous research that compared different age groups over short periods. The researchers repeatedly measured changes in fitness, muscle strength and muscular endurance in 427 Swedes born in 1958, following them for about 47 years from age 16 to 63. About half of the participants were women, allowing for a detailed analysis of how physical capacity evolves from adolescence through middle age.
"It's Never Too Late to Start Exercising"… Roughly 10% Improvement Even After Middle Age
The analysis showed that fitness generally began to decline around age 35, regardless of prior exercise history. Muscle strength and muscular endurance followed a similar pattern, with the drop becoming especially pronounced after middle age. Even when no visible changes were apparent, aging was already underway inside the body.
There were encouraging findings as well. People who began exercising regularly in adulthood saw their physical capacity, including fitness and muscle strength, improve by an average of 5 to 10 percent. The results suggest that even after the decline has begun, lifestyle changes can still deliver meaningful improvements.
Maria Westerstahl of the Karolinska Institute, who led the research, said, "There is no point at which it is too late to start exercising." She added, "Physical activity cannot stop aging itself, but it can considerably slow the pace of functional decline."
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Experts say muscle loss is not merely a matter of body shape but affects overall health. As muscle strength decreases, basal metabolic rate falls, making weight gain more likely and weakening blood sugar control. Diminished balance raises the risk of falls, while reduced daily activity can lower quality of life.
In the end, the surest way to slow aging is not a special trick but consistent movement. Walking, climbing stairs and light strength training alone can slow the pace of muscle loss.
