At 35, you're at your peak – after that, the body gradually weakens.

Long-term studies from Sweden show that physical decline begins around age 35 and accelerates significantly after age 40. Regular exercise can noticeably slow this process.

In their mid-30s, most people still feel young and energetic. Daily life runs smoothly, energy levels are sufficient, and much seems unchanged. However, long-term Swedish data show that the body gradually adapts at this age. Peak physical performance is generally reached between the ages of 20 and 30.

From around age 35, endurance and muscle strength decline, with this decline accelerating after age 40. Often, this initially goes unnoticed. Only after several years does it become clear how much the body's reserves have changed – and why exercise still has positive effects even when it is only integrated into daily life later in life.

Measurable changes in fitness from age 35

The study followed 427 women and men over several decades, from their youth to early retirement. Researchers regularly recorded values ​​such as endurance, muscle strength, and jumping ability. Unlike many previous studies that compared different age groups, this work focused on observing the same individuals over a long period.

The results paint a clear picture: Peak physical performance is usually reached between the ages of 20 and mid-30s. Afterward, a slow decline sets in, initially amounting to only a few tenths of a percent per year. From around age 40, however, this loss accelerates significantly. In old age, performance declines by more than two percent annually.

Men, on average, have higher initial values, while women reach somewhat lower values. However, the course of decline is almost identical for both sexes. This process follows a basic biological pattern and depends less on gender than on the individual's performance level and its development over the years.

Why does physical decline manifest itself differently

A surprising finding: As people age, the differences between individuals become increasingly pronounced. While some are still relatively fit at 60, others experience a significant decline in strength and stamina at an early age. Particularly in terms of stamina, the differences in old age are up to 25 times greater than in younger years.

Age alone does not fully explain these differences. Rather, long-term habits play a crucial role. Factors such as exercise, occupational stress, health challenges, and social influences interact over the course of decades. Although physical decline follows a general pattern, its pace and extent vary considerably from person to person.

Muscle strength is particularly affected. By the time they reach 63, many people have lost between 30 and 50 percent of their original capacity. Jumping ability, which is indicative of explosive power and muscle quality, declines especially sharply. These abilities are sensitive to the aging process and often go unnoticed for a long time in everyday life.

Movement influences the course.

Regular exercise not only ensures a higher initial level of physical performance but also slows down its decline. This applies to both people who were physically active from an early age and those who became physically active later in life.

Study participants who transitioned from a sedentary to a more active lifestyle in adulthood improved their physical performance. While the effects were moderate, they were stable and noticeable in the long term. In everyday life, this manifests as easier task completion, less rapid fatigue, and improved recovery. "Physical activity can slow down the decline in performance, even if it cannot completely stop it."

Regularity is crucial

The study does not identify an optimal time or fixed training plan for starting physical activity. Regularity is far more important. Even moderate exercise, such as walking, cycling, gardening, or light strength training, has a positive effect when consistently integrated into daily life.

The body responds more strongly to long-term habits than to short periods of intense motivation. Those who consistently incorporate exercise into their lives can maintain strength and endurance for longer – even if they start later in life.

Physical decline begins early – but it can be influenced.

The Swedish long-term data refute two common assumptions: First, physical decline begins earlier than often thought. Second, its progression is strongly dependent on lifestyle. Muscle mass and energy production change with age, but exercise can influence the extent of these processes.

For everyday life, this means:

• Regular exercise has a greater effect than sporadic training.
• Combinations of strength and endurance training are particularly beneficial.
• Even starting physical activity later in life brings measurable benefits.

The study will continue. In the coming years, the researchers plan to examine the participants again to better how physical performance, lifestyle, and biological changes in old age are related.

In short:

• From the age of 35, fitness slowly declines as strength and endurance measurably decrease; this process accelerates with increasing age.
• Regular exercise can slow down the decline and improve both endurance and muscle strength – even for those starting later in life.
• Sustainable movement habits are more important than early peak performances or short-term intensive training.

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