byKarolinska Institutet

Credit: CC0 Public Domain

A 47-year-long Swedish study at Karolinska Institutet reveals how fitness, strength, and muscle endurance change during adulthood. The results show that physical ability starts to deteriorate as early as age 35, but it is never too late to start exercising.

In the extensive study Swedish Physical Activity and Fitness study (SPAF), researchers followed several hundred randomly selected men and women from ages 16 to 63. The study,publishedin theJournal of Cachexia, Sarcopenia and Muscle, provides new insights into how physical capacity changes over time.

Previously, researchers relied on cross-sectional studies to gain this knowledge. The SPAF study is one of the few that, for nearly 50 years, has regularly measured fitness and strength in the same randomly selected men and women across Sweden.

The results show that fitness and strength begin to decline as early as age 35, regardless of training volume. After that, there is a gradual deterioration that accelerates with age. But the researchers also have positive news: individuals who started beingphysically active in adulthoodimproved their physical capacity by 5–10 percent.

"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. Now we will look for the mechanisms behind why everyone reaches their peak performance at age 35 and why physical activity can slow performance loss but not completely halt it," says Maria Westerstahl, lecturer at the Department of Laboratory Medicine and lead author of the study.

The research continues, and next year the participants, who will then be 68 years old, will be examined again. The researchers hope to link changes in physical capacity to lifestyle, health and biological mechanisms.

More information Maria Westerståhl et al, Rise and Fall of Physical Capacity in a General Population: A 47‐Year Longitudinal Study, Journal of Cachexia, Sarcopenia and Muscle (2025). DOI: 10.1002/jcsm.70134

Provided by Karolinska Institutet