10/21/2026
In other words get moving….
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Most people expect to start losing strength and stamina in their 60s, but in 427 Swedes tested again and again from age 16 to 63, the loss started in the mid-30s.
Westerståhl and colleagues at Karolinska Institutet (Journal of Cachexia, Sarcopenia and Muscle 2025) followed a random sample of Swedish teenagers born in 1958 for 47 years. They tested aerobic fitness on a bike, arm and chest endurance with bench press reps, and leg power with a jump test.
Aerobic fitness and bench press endurance peaked between ages 26 and 36 in both sexes. Jump power peaked earlier, at 27 in men and 19 in women. After the peak, losses started small, under 1% a year, and sped up to more than 2% a year by the early 60s. By 63, people were 30% to 48% below their peak, depending on the test. Men went from about 53 bench press reps at 35 to 34 at 63, and women from about 40 to 27. Men and women declined at the same rate.
Active people declined at the same rate as everyone else, but from a higher level, so they stayed fitter at every age. People who played sports at 16 scored higher for life. Switching from inactive to active as an adult was linked to 4% to 11% better scores, and that held at every age studied.
Other long-term studies point the same way. In the Baltimore Longitudinal Study of Aging, Fleg and colleagues found aerobic capacity fell 3% to 6% per decade in the 20s and 30s, and more than 20% per decade from the 70s on. Master athletes keep more than 80% of their peak endurance into their 60s, compared with about 65% in this cohort. Fiatarone and colleagues showed that frail nursing home residents around age 90 gained an average of 174% in strength after 8 weeks of heavy training.
The authors point to mitochondria, the energy factories in muscle cells, as an early driver in the 30s. Later come changes where nerves meet muscle, loss of muscle fibers and a weaker response to training and protein.
Because this was one cohort of Swedes born in 1958, the results may not carry over to everyone. Activity was also a single yes or no question, so the study cannot say how much or what type of exercise matters most. Links with activity do not prove cause, and people who were more educated or more active as teens were more likely to keep showing up for testing.
If you are in your 20s or early 30s, this is the window to build the highest peak you can. If you are 35 to 64, the WHO advises 150 to 300 minutes of moderate activity a week plus strength work for all major muscles on 2 or more days. If you are over 65, the WHO adds balance and strength training on 3 or more days a week to help prevent falls. If you have never trained, it is not too late to start.
Westerståhl et al., J Cachexia Sarcopenia Muscle 2025;16(6):e70134
Fleg et al., Circulation 2005;112(5):674-682
Fiatarone et al., JAMA 1990;263(22):3029-3034
Bull et al. (WHO guidelines), Br J Sports Med 2020;54(24):1451-1462