Swedish Study Shows Physical Decline Begins at 35, But Exercise Still Helps

Swedish researchers have completed a nearly 50-year study that provides rare insight into when our bodies actually start to age. The findings show that fitness and strength peak around age 35, then gradually decline as we get older. But the research also offers an encouraging message: it's never too late to start exercising and slow that decline.

The study, conducted at Karolinska Institutet in Sweden, followed more than 400 randomly selected men and women from their teenage years into their 60s. Researchers measured their aerobic capacity, muscle strength, and muscle endurance repeatedly over the decades, creating one of the most comprehensive long-term fitness studies ever completed.

Background

Most previous research on how fitness changes with age relied on comparing different age groups at a single point in time. This approach provides snapshots but misses the bigger picture of how the same person's fitness changes over years and decades. The Swedish study took a different approach by following the same people for 47 years, measuring their physical performance at regular intervals.

The participants were all born in 1958 and lived across Sweden. Researchers put them through various physical tests, including bench press exercises to measure strength, vertical jump assessments to measure power, and cycling sessions lasting at least 10 minutes to measure aerobic capacity. Over nearly five decades, they tracked how these measurements changed as the participants aged from 16 to 63.

Key Details

The results paint a clear picture of how aging affects physical performance. Fitness levels improved steadily through the teenage years and into early adulthood. But around age 35, that improvement stopped. From that point forward, fitness and strength began to decline gradually.

The rate of decline was not constant. In the years immediately following age 35, physical capacity dropped by about 0.3 to 0.6 percent per year. But as people got older, the decline accelerated. By the time participants reached their early 60s, the rate of decline had increased to about 2 to 2.5 percent per year.

When researchers looked at the overall picture, participants who were sedentary had lost between 30 and 48 percent of their peak physical capacity by age 63. Those who remained active fared better, but even regular exercisers showed the same basic pattern of decline.

The study also found some differences between men and women. Aerobic endurance began declining around the mid-40s for both sexes. But muscle power started declining earlier in women, beginning in the early 30s, while men experienced this decline a few years later. Despite these differences, the long-term rate of decline was similar between the two groups.

The Exercise Factor

One of the most striking findings was that people who became physically active during adulthood still improved their physical capacity by 5 to 10 percent. This suggests that while the overall trend of decline is unavoidable, exercise can slow it down significantly.

"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, the lead author of the study.

Westerståhl added that the researchers now plan to investigate why everyone reaches peak performance around age 35 and why exercise can slow performance loss but not halt it entirely.

What This Means

The findings challenge the common assumption that physical decline is something that happens only to older people. The research shows that our bodies start to age much earlier than many people realize. But the study also makes clear that this decline is not inevitable or unstoppable.

The single most important factor in determining how much fitness a person retains as they age is physical activity. People who exercise regularly maintain more of their peak capacity than those who are sedentary. This holds true even for people who start exercising later in life.

For someone in their 50s or 60s who has never exercised regularly, the research suggests that starting now could still produce meaningful improvements. A 5 to 10 percent increase in physical capacity might not sound dramatic, but it can make a real difference in everyday life, affecting everything from the ability to climb stairs to maintaining balance and avoiding falls.

The researchers also noted that elite athletes follow the same pattern as the general population. They too peak in their mid-30s. But because they start from a higher baseline, they maintain more absolute fitness capacity later in life. By age 63, elite athletes in the study had retained more than 80 percent of their peak endurance capacity, compared with about 65 percent among the other participants.

The study is ongoing. Researchers plan to examine the participants again next year when they reach age 68. They hope to better understand how changes in physical performance connect to lifestyle choices, overall health, and the biological processes underlying aging.