A comprehensive 47-year study conducted by researchers at Karolinska Institutet in Sweden has found that physical ability begins to decline at age 35. The findings, published in the Journal of Cachexia, Sarcopenia and Muscle on December 16, 2025, highlight significant changes in fitness, strength, and muscle endurance throughout adulthood.
The research, known as the Swedish Physical Activity and Fitness study (SPAF), involved several hundred randomly selected men and women aged between 16 and 63. This longitudinal study stands out as one of the few that has consistently measured fitness and strength over nearly five decades in a diverse group across Sweden.
Key Findings on Physical Decline and Exercise Benefits
Results indicate a gradual deterioration of physical capabilities that begins at age 35, which occurs irrespective of an individual’s training volume. Following this age, the decline becomes more pronounced as individuals grow older. Despite these findings, researchers emphasize that it is never too late to begin exercising. Those who took up physical activity later in life saw an improvement in their physical capacity by as much as 5-10 percent.
Lead author of the study, Maria Westerståhl, who is a lecturer at the Department of Laboratory Medicine, stated, “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.” This offers a hopeful perspective for individuals concerned about aging and physical fitness.
Future Research Directions
The SPAF study will continue, with plans to re-examine participants next year when they reach the age of 68. The researchers aim to explore the links between changes in physical capacity, lifestyle choices, health conditions, and underlying biological mechanisms. This ongoing research could provide deeper insights into how aging affects physical fitness and the potential role of exercise in mitigating these effects.
The findings underscore the importance of maintaining an active lifestyle, especially as individuals transition into middle age and beyond. Understanding the mechanisms behind peak performance at age 35 and the effects of physical activity on performance decline remains a crucial focus for the research team.
As this study progresses, it holds the potential to reshape how society views aging and physical fitness, encouraging a culture of health and activity among older adults.
