What decades of follow-up reveal about physical capacity

# What decades of follow-up reveal about physical capacity OCTOBER 15, 2026 | LONGEVITY SPECIAL Physical fitness in a general population appears to peak between the mid-20s and mid-30s, then slip a little more each year for decades, according to a Swedish study that tested the same people from age 16 to 63. The study measured aerobic capacity, muscular endurance and leg power. It did not track strength over time: grip strength was measured only at 63. Some news coverage describes the findings as a decline in strength. A long study lets us see change that a short experiment cannot. Following physical capacity across 47 years makes its trajectory visible, while reminding us how much variation a single age threshold can conceal. The work is an observational study, published in 2025 in the Journal of Cachexia, Sarcopenia and Muscle. It followed 427 people (48% women), all born in 1958 and randomly selected as a representative sample of Swedish teenagers. Observational means the researchers measured people over time. They did not assign anyone to an exercise programme. The team, led by Maria Westerståhl at Karolinska Institutet, tested the group at ages 16, 27, 34, 52 and 63. The tests covered aerobic capacity, muscular endurance and leg power. From age 27 on, aerobic capacity was estimated from a cycling test at a moderate effort, not an all-out test. At age 16 it was estimated from a 9-minute run, converted using data from a subgroup who also did the cycle test. Muscular endurance was the number of bench press lifts. Leg power was measured with a jump test. Estimated aerobic capacity and muscular endurance peaked at ages 26 to 36 in both sexes. After that, they declined gradually. The yearly loss started at 0.3% to 0.6% and rose to 2.0% to 2.5% per year. For total aerobic capacity, the peak came at 35 in women and 36 in men. The rate of loss was about 0.5% a year at age 40 and about 2% a year at 63. From peak to age 63, the cumulative drop was 30% in women and 33% in men. Fitness measured per kilogram of body weight peaked earlier in men, at 26, than in women, at 31. From about age 40, the decline was similar in both sexes. The gap between individuals also widened. By 63, the spread in total aerobic capacity was five times larger than at the start. Most people in the group were not frail at 63. Using standard European cut-offs for weak grip or slow chair rising, no men and four women fell below the line. The authors say the pattern matches what is known from elite athletes. They conclude that a decline in physical capacity can be seen before 40 and can later lead to clinically significant problems, especially in sedentary people. The news coverage went further on exercise. ScienceDaily, which republished a Karolinska Institutet release, said people who became active in adulthood improved their physical capacity by about 5% to 10%. It also said average performance across measures was 30% to 48% below peak by 63. The portion of the paper available to us confirms the 30% and 33% aerobic figures but does not show the other numbers. Those should be treated as the coverage's account. The paper does not show that exercise stops the decline. Its physical activity data came from a simple yes-or-no question about leisure-time activity. That cannot capture how hard or how long anyone trained. People with a university degree or an active youth were also more likely to take part. The authors included the whole starting cohort in their models to limit bias from dropouts. Westerståhl said in the Karolinska Institutet release carried by ScienceDaily: "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." She added that the team will now look for the mechanisms behind the peak at about 35. A second paper from the same cohort, in Scientific Reports in 2026, links earlier fitness to artery health. Higher aerobic capacity at 34 and at 52 predicted lower arterial stiffness at 63. The association held after accounting for obesity, smoking, blood pressure and HDL cholesterol. It is also an observational finding, so it does not prove that fitness caused healthier arteries. Taken together, the studies suggest that fitness in the 30s and 40s matters for later life. The data show when decline begins and how fast it speeds up. They do not show how much exercise is needed to change the course. The researchers' next step is to look for the biology behind the early peak and why activity slows the loss but does not halt it. A population curve describes what happened in a group. The clinical task is to understand an individual's capacity and what can still be developed from there. Sources: Journal of cachexia, sarcopenia and muscle (2025), ScienceDaily (Karolinska Institutet; Journal of Cachexia, Sarcopenia and Muscle) Journal of cachexia, sarcopenia and muscle (2025): https://doi.org/10.1002/jcsm.70134 ScienceDaily (Karolinska Institutet; Journal of: https://www.sciencedaily.com/releases/2026/10/261014000912.htm ---