Science Reveals When Fitness and Strength Begin to Fade

A long-running Swedish study conducted at Karolinska Institutet has followed people for 47 years to examine how fitness, strength, and muscle endurance evolve during adulthood. The findings show that physical performance begins to decline around age 35. At the same time, the research shows that starting to exercise later in life can still yield meaningful benefits.

The research is part of the Swedish Physical Activity and Fitness study (SPAF), which tracked several hundred randomly selected men and women aged 16 to 63. Published in the Journal of Cachexia, Sarcopenia and Muscle, the study offers rare long-term insight into how physical capacity changes over decades rather than snapshots at a single point in time.

The results show that both fitness and strength start to decrease as early as age 35, regardless of how much people trained earlier in life. Physical decline continues gradually and tends to speed up with advancing age. Despite this pattern, the researchers found encouraging evidence that exercise remains valuable at any stage. Participants who became physically active in adulthood increased their physical capacity by 5-10%.   

"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 Westerståhl, lecturer at the Department of Laboratory Medicine and lead author of the study.