Study: Fitness Decline Begins at 35, Even in Active Adults — SkimNews
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- Karolinska Institutet researchers tracked 427 Swedish men and women born in 1958 from age 16 to 63, finding aerobic fitness and muscular endurance peaked between ages 26 and 36 before beginning a steady decline.
- Even participants who remained physically active showed performance declines starting around age 35, with average measures falling 30-48% from peak levels by age 63, at similar rates in men and women.
- Participants who began exercising in adulthood saw 5-10% improvements in physical capacity, and those active since adolescence maintained better fitness, endurance, and muscle power throughout life.
- A 2026 follow-up in Scientific Reports linked better aerobic fitness at ages 34 and 52 to less arterial stiffness at age 63, independent of obesity, smoking, and blood pressure.
- Lead author Maria Westerståhl said biological changes, not just reduced activity, appear to drive the decline — though she emphasized that "it is never too late to start moving" since exercise slows the loss.
- The researchers plan next-round assessments when participants reach age 68 to investigate which lifestyle factors and biological mechanisms sit behind the age-35 turning point.
Why it matters: For this 47-year Swedish cohort, physical decline averaged 30-48% from peak by age 63 — a trajectory even active adults couldn't fully avoid but could noticeably moderate. The 5-10% gains seen in those who started exercising in adulthood show becoming active at 35, 50, or later still moves the needle on measurable fitness and arterial health by retirement age.
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