Physical strength, endurance, and overall fitness don’t stay the same forever. A new long-term study highlights a key age when the body begins to show signs of decline—even in those who exercise regularly. Understanding these changes can help adjust workout routines and maintain fitness levels longer.
A 47-year-long study published in the Journal of Cachexia, Sarcopenia and Muscle tracked physical fitness in over 400 men and women, ranging from 16 to 63 years old. Conducted by the Swedish Physical Activity and Fitness study at Karolinska Institutet, the research monitored participants through exercises like bench presses, vertical jumps, and cycling to measure muscle endurance, strength, and cardiovascular capacity.
The results were clear: physical fitness reaches its peak around age 35. After this point, both muscle strength and cardio endurance begin to decline gradually. These changes occur regardless of prior activity levels, meaning even those who consistently worked out in their 20s and early 30s experience a slight decrease in performance.
Differences Between Men and Women
Freepik | Muscle power fades earlier for women (32), but endurance dips at 45 for everyone.
While the general trend applies to everyone, slight differences exist between sexes. Women tend to experience a decline in muscle power earlier, starting around age 32, while both men and women see aerobic endurance start to drop around age 45.
During the teen years and 20s, participants showed steady improvements in strength and fitness, but after hitting 35, the trajectory shifts. Gains slow down and then gradually reverse, marking a natural turning point in physical performance.
The Role of Early and Consistent Activity
The study also emphasizes the benefits of maintaining an active lifestyle from a young age. Participants who became physically active at 16 and continued into adulthood performed better across all fitness tests compared to those who started later.
Freepik | The study shows staying active at any age helps slow fitness decline and supports better health over time.
The study’s lead author, Maria Westerstahl, who lectures in the Department of Laboratory Medicine, said the results challenge the idea that it’s too late to benefit from exercise. “It is never too late to start moving,” she explained, pointing out that physical activity can slow declines in performance, even if it cannot eliminate them.
Similar conclusions appear throughout the research literature. Studies repeatedly show that staying active into older age helps protect mobility and strength, contributing to better endurance and improved quality of life as the body changes over time.
Ongoing Research
The study is continuing, tracking participants now up to age 68. Researchers aim to uncover why peak performance consistently occurs at 35 and how physical activity mitigates, but cannot fully prevent, declines in strength and fitness.
Gaining insight into this natural decline makes it easier to plan effective fitness routines later in life. As the body ages, prioritizing strength training helps preserve muscle power, while incorporating aerobic exercises supports cardiovascular health.
Perhaps most importantly, beginning physical activity early and maintaining consistency over the years plays a crucial role in sustaining overall fitness and strength.