THE ARISING · Longevity & Healthspan
Swedish 47-Year Study: Aerobic Fitness and Endurance Peak Between 26 and 36
Physical capacity in ordinary adults appears to peak between the mid20s and mid-30s and then slowly fall, according to a 47-year Swedish study in the Journal of Cachexia, Sarcopenia and Muscle. Strength was not tracked across the decades; the study followed aerobic capacity, muscular endurance and leg power, with grip strength measured only at 63. Press coverage describes the finding as 'fitness and strength' declining around 35, but the paper's peaks range from 26 to 36.
This is an observational study in people. It followed 427 individuals (48% women), all born in 1958 and randomly selected as 16-year-old pupils in 1974 to represent Swedish adolescents. They were tested at ages 16, 27, 34, 52 and 63. An observational study can describe a pattern. It cannot prove what causes it.
The team measured aerobic capacity, which is how well the body uses oxygen during effort. They estimated it with a submaximal cycle test. At age 16 they converted a 9minute run result instead. They also measured muscular endurance with bench press repetitions, and leg power with a standing jump test.
Estimated aerobic capacity and muscular endurance peaked between ages 26 and 36 in both sexes. The decline then began at 0.3% to 0.6% per year. By age 63 it had sped up to 2.0% to 2.5% per year, according to the paper.
Total (absolute) aerobic capacity peaked at 35 in women and 36 in men. From that peak to age 63, it fell by 30% in women and 33% in men. Aerobic capacity adjusted for body weight peaked earlier in men (age 26) than in women (age 31). From about age 40, the rate of decline was similar in both sexes.
People also drifted apart over time. The spread in absolute aerobic capacity between individuals grew fivefold from age 16 to 63. At 63, no men and four women fell below the European cut-offs for low grip strength or slow chair stands, which are used to flag sarcopenia, the age-related loss of muscle. Decline in the group, then, did not mean disease for most people.
The authors say the pattern matches what is seen in elite athletes, who tend to peak around 35 even while training. They conclude that a decline in physical capacity can be seen before age 40. They add that it can later lead to clinically significant physical problems, especially in people with a sedentary lifestyle. That is their interpretation of the pattern, not something the study tested directly.
The press coverage went further on exercise. ScienceDaily, relaying a Karolinska Institutet release, reports that average performance at 63 was roughly 30% to 48% below peak. It also reports that people who became active in adulthood improved their capacity by about 5% to 10%. Those figures come from that coverage, not from the parts of the paper reviewed here. ScienceDaily quotes lead author Maria Westerståhl: "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."
A separate paper from the same cohort, in Scientific Reports in 2026, looked at the heart and blood vessels. Higher aerobic capacity at 34 and at 52 predicted less arterial stiffness at 63, a marker of cardiovascular risk. The link held after accounting for obesity, smoking, blood pressure and cholesterol measures. The design is observational. The authors' wording leans toward cause, suggesting that maintaining aerobic capacity from early adulthood can reduce arterial stiffness and cardiovascular risk, but the data show an association. The press coverage says plainly that the results do not establish that better fitness directly prevented arterial stiffening.
There are limits. The cohort is a single birth year from one country. The study says people with a university degree or an active youth were more likely to keep taking part, though the analysis included everyone from the start to reduce that bias. Activity was recorded with a simple yes-or-no question. Aerobic capacity was estimated, not directly measured. The study also describes group averages, so no one should treat 35 as a personal deadline.
The authors say their next step is to look for the biological mechanisms behind the early peak and behind exercise's partial protection.
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