Physical fitness and strength peak in your late 20s and early 30s, then gradually decline starting around age 35, according to a major long-term Swedish study. But the research also reveals an encouraging finding: it's never too late to start exercising and see real improvements in your physical capacity.

Researchers at Karolinska Institutet tracked 427 randomly selected men and women from age 16 through their early 60s as part of the Swedish Physical Activity and Fitness study (SPAF). The study, published in the Journal of Cachexia, Sarcopenia and Muscle, tested the same participants repeatedly over nearly five decades, making it one of the rare long-term investigations that can track how bodies change across an entire lifespan.

When Does Physical Performance Peak?

The researchers found that aerobic capacity and muscular endurance peaked between ages 26 and 35. For muscular power specifically, the findings differed slightly by sex: men's power peaked at age 27, while women's peaked at age 19.

After age 35, the decline becomes measurable. Fitness gradually decreases by approximately 0.3 to 0.6 percent per year, then accelerates to 2 to 2.5 percent annually as people approach their 60s. This decline affects strength, fitness, and muscle endurance across the board, regardless of participants' training backgrounds.

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

Maria Westerståhl, Lecturer at the Department of Laboratory Medicine, Karolinska Institutet

Can You Reverse Fitness Decline by Starting Exercise Later?

One of the most encouraging findings from the research is that it's not too late to improve your physical capacity, even if you haven't been active for years. People who took up exercise in later life still improved their physical capacity by 5 to 10 percent. This suggests that starting a fitness routine at any age can deliver meaningful gains.

The researchers plan to continue following this group as they age to examine how lifestyle, health, and biological processes shape physical performance over a lifetime. For anyone worried about aging and fitness, the message is clear: consistency and movement matter more than starting young.

How to Build a Heart-Healthy Exercise Routine

While the Swedish study focused on when fitness peaks and declines, another key finding from recent research emphasizes that cardiovascular health depends on combining different types of exercise. A review published in the Journal of the American Heart Association analyzed nearly 500 peer-reviewed studies and found that maintaining strong cardiovascular health improves outcomes far beyond just heart function.

The benefits of heart-healthy exercise extend to better brain function, stronger muscles, improved vision and hearing, and lower risk of chronic diseases including diabetes, dementia, and some cancers. The review examined the American Heart Association's Life's Essential 8 metrics, which include physical activity, nutrition, sleep, blood pressure, cholesterol, blood sugar, weight management, and not smoking.

• Brisk Walking: Start with daily 20 to 30 minute brisk walks where you can talk but feel slightly breathy, not gasping or leisurely strolling. Walking alone lowers blood pressure and improves insulin sensitivity, with added blood sugar control if you place walks after meals.
• Strength Training: Add two days per week of short strength sessions after establishing a walking routine. Strength training supports cardiovascular health by improving insulin sensitivity, reducing inflammation, lowering triglycerides, and preventing visceral fat buildup, even without weight loss.
• Cardio Sessions: Include one to two short cardio sessions on different days from strength work. Cardio trains the heart as its own muscle, lowering resting heart rate and blood pressure while improving circulation, stamina, and cholesterol levels.

"Both cardio and strength training are essential for overall health and longevity, and they improve the heart in multiple ways. You cannot have one without the other for optimal health and longevity," explained Jess Schneider, a certified personal trainer and behavior change coach at Life Time Westchester in New York.

Jess Schneider, Certified Personal Trainer and Behavior Change Coach, Life Time Westchester

The key to success is gradual adaptation rather than shock to the system. After about two weeks of consistent daily walks, add structure with strength and cardio sessions on different days. This approach helps prevent burnout and allows your body to adapt sustainably.

What Else Supports Long-Term Fitness and Recovery?

Exercise is foundational, but it's only part of the picture. Sleep, stress management, and nutrition also shape how your body responds to training and how quickly you recover. Consistent, high-quality sleep plays a critical role in regulating blood pressure, stress hormones, and inflammation.

Most adults need seven to nine hours of sleep, and sleep quality starts with a consistent bedtime and waking schedule. Poor sleep raises blood pressure, inflammation, hunger hormones, and resting heart rate while reducing cognitive and metabolic function over time.

Recovery is equally important as the workouts themselves. Without adequate recovery between intense sessions, muscles become fatigued, making it harder to maintain proper form and increasing injury risk. Taking rest days between intense workouts, increasing training gradually instead of making sudden jumps in intensity, and stretching regularly all support long-term fitness gains.

The bottom line: while physical decline is inevitable as we age, regular exercise, proper recovery, good sleep, and consistent movement can slow that decline significantly. Whether you're 35 or 65, the research shows that starting or maintaining an exercise routine delivers real, measurable improvements in how you feel and function every day.