Fitness, strength and stamina takes a critical turn after age 35, warns study

A rare long-term study from Sweden shows physical fitness peaks around 35 and declines gradually — but adults who start moving later still see a 5–10% improvement. (Image: Pexels)

• Fitness and strength start to decline around age 35, study finds
• Exercise begun in midlife can boost physical capacity by up to 10 percent
• Consistent activity slows ageing's impact but cannot fully prevent decline

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For many people, ageing feels like a slow, invisible process. One day you sprint for the bus without thinking, and the next, your knees protest. Now, a rare long-term study from Sweden has put a number on that moment of change, offering both a wake-up call and a reassuring message.

Conducted by researchers at Karolinska Institutet, the study followed adults for nearly half a century, tracking how fitness, strength and endurance evolve across adulthood. Its suggests physical performance begins to dip around the age of 35. However, it also delivers good news for anyone who believes they’ve “left it too late”.

The research forms part of the Swedish Physical Activity and Fitness (SPAF) study, one of the longest of its kind. Unlike many earlier studies that compared different age groups at a single moment in time, this project repeatedly measured the same individuals over decades. Participants, aged between 16 and 63 at the start, were assessed again and again as their lives unfolded.

Also Read: Healthy ageing: Age is just a number, unless you fail these 5 tests

The results show that both fitness and muscular strength start to decline in the mid-thirties, regardless of how active someone was earlier in life. From that point, the downward trend continues gradually and accelerates with age. In simple terms, the body’s peak performance window appears to close sooner than many expect.

What makes this study particularly powerful is its human relevance. It reflects real lives, not lab conditions. Careers change, families grow, injuries happen and routines slip. By following the same people for 47 years, the researchers captured how ageing truly plays out beyond gym memberships and New Year resolutions.

Perhaps most encouraging is the finding that exercise still works, even when started later. Adults who became physically active in midlife improved their physical capacity by five to ten percent. That improvement may not stop ageing, but it meaningfully slows its impact.

Maria Westerståhl, the study’s lead author, summed it up simply: it is never too late to start moving. Physical activity cannot completely prevent decline, but it can delay it, soften it and improve quality of life along the way.

Here’s what the study says

• Fitness and strength begin to decline around age 35
• Physical decline accelerates gradually with age
• Past activity doesn’t fully protect against decline
• Starting exercise later can still improve capacity by up to 10%
• Consistent movement helps slow, though not stop, physical ageing

Also Read: You can slow biological ageing with simple lifestyle changes, here's how

Researchers plan to reassess participants at age 68, hoping to uncover how lifestyle, biology and long-term health are connected. For now, the message is clear and empowering: while time moves forward, staying active gives us more say in how we move with it.

FAQs on how age 35 is a turning point for overall health

Why is age 35 considered a turning point for overall health?

The study from Karolinska Institutet indicates that physical performance begins to decline around this age, marking the start of a gradual and accelerating downward trend in fitness and muscular strength.

Can past physical activity protect against this decline?

While past activity offers some benefits, it does not fully protect against the decline that begins around age 35.

Is it too late to start exercising after 35?

No, the study found that adults who started exercising later in life improved their physical capacity by five to ten percent, demonstrating that exercise still has significant benefits even when begun after 35.

How does consistent movement impact ageing?

Consistent physical activity helps to slow the ageing process, though it cannot completely stop it, and it significantly improves the quality of life.

Disclaimer: This article, including health and fitness advice, only provides generic information. Don’t treat it as a substitute for qualified medical opinion. Always consult a specialist for specific health diagnosis.