We all know that once we get passed a certain age, no matter how much we may workout, we simply are not as strong as we used to be. A new long-term study narrows down exactly when the decline tends to start. You may be surprised that it’s as young as 35!
The long-term study, conducted at the Karolinska Institutet as part of the Swedish Physical Activity and Fitness study (SPAF), tracked 427 people over the course of almost 50 years. Researchers repeatedly assessed their physical capacity from age 16 to 63 and found that their fitness and strength levels declined by 30%-48%.
“The study shows that fitness and muscle strength begin to decline relatively early, around the age of 35, and this decline follows a gradual pattern throughout adulthood,” said Maria Westerståhl, lecturer at the Karolinska Institutet and lead author of the study. “Rather than dropping suddenly, physical capacity decreases slowly over time and accelerates as people age, making losses more noticeable later in life.”
Several factors influence how quickly strength and fitness decline with age, but physical activity appears to be one of the most important. Researchers found that people who remain active throughout life—or even start exercising later—tend to experience a slower decline and may even improve their capacity to some extent. In contrast, a sedentary lifestyle can accelerate these losses.
“This decline is linked to biological changes associated with aging, including gradual loss of muscle mass, changes in muscle fiber composition, and reduced efficiency in how the nervous system activates muscles,” Westerståhl said. “Broader processes such as altered metabolism, hormonal changes, and increased inflammation also contribute, and these changes typically begin many years before the decline becomes clearly noticeable.”
Women May See Changes Earlier Than Men
The study found that women may experience declines in muscle power slightly earlier than men, but both sexes show similar declines in endurance over time.
Certain sex differences may be attributed to varying hormonal changes, which can include menopause as a leading accelerator of muscle and bone loss in women, said Leada Malek, PT, DPT, an adjunct professor at Samuel Merritt University and a spokesperson for the American Physical Therapy Association.
“In my own experience as a physical therapist, I see many women seek physical therapy for improving capacity around perimenopause and menopause, whereas men may seek assistance later due to a more gradual decline,” Malek said.
Why Exercise Is So Important for Healthy Aging
Despite these age-related processes, some of which are unavoidable, Westerståhl said staying active remains highly beneficial. Even starting physical activity later in life can improve strength and fitness and help slow the rate of decline, even if it cannot completely stop it, she said.
Muscular strength and power, endurance, and aerobic fitness naturally diminish over time unless the body is provided with the appropriate stimulus to continue to adapt and combat these changes, Malek said.
“When I work with patients experiencing this shift, it typically looks like a loss in mobility, balance, flexibility, and overall functional ability,” she explained. “I work with patients who aren’t able to participate in or who experience more difficulty completing routine tasks, like mowing the lawn, cleaning, or gardening.”
The good news is, that although we cannot turn back the clock, regular activity can slow these declines, as well as their associated risk for falls, chronic disease, and loss of independence, she said.
“Just as the study found that adults who became active later in life improved their physical capacity (by 5–10%), I see similar outcomes regularly with my long-term patients,” she said. “We’re able to recover lost strength in mobility by implementing the best movements for their needs, at the appropriate dose and intensity to drive positive change.”
