You start to physically slow down subtly in your 30s, with muscle strength and aerobic capacity declining gradually, but significant, noticeable slowing often becomes apparent in the 50s and 60s due to faster muscle loss (sarcopenia), reduced heart function, and slower recovery, though physical activity greatly influences the rate of decline, with studies showing declines starting as early as 35 for some abilities and exercise potentially reversing many age-related issues.
Declines in walking speed and aerobic endurance became evident in the 60s and 70s. More physical activity was associated with less physical decline, especially in ages 60 to 79.
The speed that your body burns energy for its everyday functions is called your metabolic rate. For most people, this doesn't start to slow down until around the age of 60, but it does change if your weight changes.
Endurance athletes begin to slow in the mid- to late 30s. The rate of decline increases with aging.
Age and Performance
It's generally accepted that VO2 max – the maximum amount of oxygen you can take in and deliver to tissues – starts declining at around 40 years old and declines at around 1-2% per year thereafter. In other words, you could lose 10-20% of maximum aerobic capacity between 40 and 50!
Despite these proven benefits, exercise and physical activity rates among older people are surprisingly low. Only about 30% of people ages 45 to 64 say they engage in regular leisure-time physical activity. This falls to 25% of those between the ages of 65 and 74 and 11% of people age 85 and older.
Exposure to light is a top cause of premature aging: Sun exposure causes many skin problems. Ultraviolet (UV) light and exposure to sunlight age your skin more quickly than it would age naturally. The result is called photoaging, and it's responsible for 90% of visible changes to your skin.
The observed age pattern for daily stress was remarkably strong: stress was relatively high from age 20 through 50, followed by a precipitous decline through age 70 and beyond.
Yes, it's true that a very small percentage of people run a marathon, with estimates suggesting less than 1% of the world's population has ever completed one, and some sources place the annual participation even lower, around 0.01% to 0.1% of the global population. While millions finish marathons yearly, the total number of individuals who have ever completed the 26.2-mile (42.195 km) distance is a small fraction of the total world population.
Massive biomolecular shifts occur in our 40s and 60s, Stanford Medicine researchers find. We undergo two periods of rapid change, averaging around age 44 and age 60, according to a Stanford Medicine study.
Recent scientific research has identified three critical ages-34, 60, and 78—when the human body undergoes significant biological aging.
The 40s and 50s
Both fluctuations can result in lower energy levels, feeling lethargic, and less muscle mass. Again, the 40s and 50s impact people differently, with some noticing fewer effects than others. However, during this stage, people will usually notice they're "getting old".
In the short term, lack of sleep can cause a decline in motor skills, slow down information processing, reduce our attention spans and emotional capacity, and impair our judgement. Over the long term, sleep issues can lead to a higher risk of cognitive decline, impaired memory and Alzheimer's disease.
“Being physically active is the best gift that you can give to yourself,” he says. Other measures he recommends include not smoking, maintaining a healthy weight, getting good sleep, getting all recommended vaccines, getting preventive cancer screenings, and treating hypertension and high cholesterol.
The 70/30 rule in fitness suggests that 70% of your physical results (especially weight loss and body composition) come from nutrition and diet, while only 30% comes from exercise (gym workouts), emphasizing that what you eat is far more crucial for changing your physique than just working out, though both are important for overall health and muscle building. It highlights that while the gym breaks down muscles (the 30% effort), the kitchen (the 70%) provides the essential fuel, protein, and rest for them to repair and grow stronger.
Signs you're aging well include physical vitality (easy movement, good balance, strength for daily tasks), sharp cognitive function (curiosity, learning new skills, remembering details), and strong emotional/social health (staying connected, finding purpose, managing stress). It's about maintaining independence, a positive mindset, and actively engaging in activities you enjoy, not just looking younger, though good skin/hair can be indicators too.
The 80/20 rule in running is a training principle suggesting you should spend 80% of your training time at an easy, conversational pace (low intensity) and only 20% at a harder, more intense effort (high intensity), like tempo runs or intervals, to build aerobic fitness, improve performance, and prevent burnout. Developed by exercise physiologist Stephen Seiler, it combats the common mistake of running too many days in a moderate "gray zone," which hinders adaptation, and helps runners build a stronger aerobic base to support faster speeds.
The 10-10-10 marathon rule is a popular pacing strategy that splits the 26.2-mile race into three manageable sections: the first 10 miles, the next 10 miles (miles 11-20), and the final 10 kilometers (6.2 miles). The goal is to run the first 10 miles conservatively, slightly slower than goal pace, then settle into goal pace for miles 11-20, and push hard in the final 10K to finish strong, conserving energy early to avoid burnout and the dreaded "wall".
Have you heard coaches (or parents) say, "Running is 90 percent mental." That's a silly idea. If that were true, there would be tens of thousands of aspiring high school athletes lying on their backs in bed visualizing their way to PRs (though there is a ton of value in visualization, which I'll get to in a moment).
Surprising Science: The 2 Ages When People Are Happiest
According to a study by the London School of Economics and Political Science, happiness tends to peak not once, but twice in life: first at age 23, and again at age 69. Yes—69!
In it, he talks about how the ages of 22–42 are statistically the most unhappy period in life. Why? People come out of their early 20s and think life is supposed to be easy, but it's not. Those two decades are full of challenges.
Quality of life increases from 50 years (CASP‐19 score 44.4) to peak at 68 years (CASP‐19 score 47.7). From there it gradually starts to decline, reaching the same level as at 50 years by 86 years. By 100 years, CASP‐19 score has declined to 37.3.
A peanut butter and jelly sandwich (PB&J) adds about 33 minutes to your healthy lifespan per serving, according to a University of Michigan study that measured life expectancy impacts of over 5,850 foods using the Health Nutritional Index (HNI). This sandwich tops the list for adding time, with nuts and seeds also being highly beneficial (around 25 mins) and processed items like hot dogs subtracting time.
The Japanese diet is low in processed foods and added sugars and high in fresh vegetables, seafood, soy products, and rice. This diet is rich in antioxidants, vitamins, and omega-3 fatty acids, which help fight oxidative stress and inflammation, two major causes of aging.
Italy's youth are facing obesity because of what Longo calls the “poisonous five P's—pizza, pasta, protein, potatoes, and pane (or bread),” Jason Horowitz writes in the NYT. Longo fears Italians will live long but not healthfully if this pattern continues to dominate the culture.