The Role of Physical Activity in Successful Aging

By: Helena Zhang and Marcia Stefanick, PhD

Physical activity is considered of utmost importance in the field of research on successful aging. However, the question of what physical activity should look like throughout one’s lifetime remains. While walking is an excellent way to begin exercising, it may not be sufficient for healthy aging in the long run. Instead, research suggests incorporating a variety of exercise modalities into your routine to improve overall health and well-being throughout life. Resistance training – which involves weights, resistance bands, and body weight exercise – plays an important role in muscle and bone density and cardiovascular health. The value of proprioception in physical activity is also emphasized. Proprioception is the body’s ability to orient and sense its own movement and is important for safe and efficient movement throughout life.

    Balance exercises improve the mind-muscle connection and can help to prevent falls. These exercises include Tai Chi and Yoga, which are low-intensity physical activities that increase cerebral blood flow and involve sustained attention. Furthermore, endurance exercises, such as running or swimming, reduce inflammation, improve cardiovascular health, and can result in healthy gut microbiomes (Clauss et al. 2021 and Estaki et al. 2016). Members of the Stanford Lifestyle Team are currently researching the role of physical activity in successful aging. To learn more about an ongoing physical activity intervention trial for cardiovascular disease prevention keep on reading!

Key Guidelines for Older Adults

For substantial health benefits, adults should at least do either: 150 minutes to 300 minutes a week of moderate-intensity physical activity 75 minutes to 150 minutes a week of vigorous-intensity aerobic physical activity or an equivalent combination of moderate- and vigorous-intensity aerobic activity. With aerobic activity preferably spread throughout the week

Additional health benefits are gained by engaging in physical activity beyond these hours. Adults should also do muscle-strengthening and balance activities on 2 or more days a week.

  • Balance activities can improve the ability to resist forces within or outside of the body that causes falls.
  • Balance training examples include walking heel-to-toe, practicing standing from a sitting position, and using a wobble board. Strengthening muscles of the back, abdomen, and legs also improves balance.


Our Team’s Research

Women’s Health Initiative Strong and Healthy (WHISH): A pragmatic physical activity intervention trial for cardiovascular disease prevention

While national guidelines promote physical activity to prevent cardiovascular disease (CVD), the Women’s Health Initiative Strong and Healthy (WHISH) study is the first randomized control trial to test the effectiveness of increasing physical activity for cardiovascular prevention in older women. The WHISH trial is unique in its scale and study design. 49,333 women aged 68 to 99 were randomly assigned to two groups. While one group received a physical activity program, the other group continued with their usual activities. After 8 years of follow-up, the study aims to compare the heart health of these two groups. For the group that was assigned to the intervention, a multi-component physical activity intervention is being delivered.

Based on intervention goals from the U.S. Department of Health and Human Services, the physical activity program in WHISH aims to increase or maintain aerobic physical activity (primarily walking), decrease sedentary behavior (especially sitting), and increase multicomponent physical activity regarding muscle-strengthening, balance, and flexibility. The intervention is delivered through multiple channels including quarterly (seasonal) WHISHful Actions newsletters, with inserts targeted at 3 participant groups based on lower, middle and higher levels of self-reported physical functioning and physical activity levels, monthly telephone calls and emails with motivational messages, and access to exercise resources on the WHISH website. Crucial to our understanding of CVD prevention in older women, the comprehensive and pragmatic approach of the WHISH study make it a landmark study that will inform policy and future research.

Learn more about the WHISH study here:

WHISH PI: Dr. Marcia L. Stefanick

Dr. Stefanick is a Professor of Medicine, Professor of Obstetrics and Gynecology, and a member of the Lifestyle Medicine Program at Stanford University. Her research focuses on chronic disease prevention in men and women. She is the Principal Investigator of the Women’s Health Initiative Strong and Healthy (WHISH), a large-scale physical activity intervention trial investigating whether moving more and sitting less can reduce risk of heart disease in older women.

Stop the Clock

Stop The Clock: The Shocking Truth About Age-Related Muscle Loss and Steps to Fight Back


By: Sarita Khemani, MD

As a physician specializing in peri-operative medicine, I have witnessed firsthand the detrimental impact of muscle loss on patients. Whether it is individuals presenting with hip or spine fractures, or those who have suffered from bleeding in their brain following a fall, many of these acute conditions have a hidden underlying cause: the loss of muscle mass.

Although losing muscle may not seem like a significant concern, it can be a silent yet deadly issue that progressively drains our vitality and strength, leading us to become frail and dependent.

In this blog, we will explore the latest scientific research on the trajectory of muscle loss as we age and discuss practical steps that we can take to prevent or alleviate its effects.

Understanding Skeletal Muscle: Composition and Function

Skeletal muscle is the type of muscle tissue that we can control voluntarily, such as when we intentionally flex our biceps or perform other movements. It is composed of many smaller bundles of muscle fibers, each containing hundreds to thousands of individual fibers. These fibers are primarily made up of two proteins: myosin and actin, which work together to facilitate muscle contraction.

The muscle fibers themselves are arranged in a specific pattern, extending the muscle’s length between the tendinous ends, and are bundled together and wrapped in connective tissue. This arrangement allows the muscle to generate force and produce movement when it contracts.

In terms of composition, muscle tissue is approximately 70% water and 30% protein. The body synthesizes muscle protein from the amino acids that are present in the protein we consume through our diet.

Image credit: University of Miami:


As we age, the gradual decline in muscle mass and strength worsens with each passing decade. This decline can be attributed to several factors, including reduced dietary protein intake, decreased physical activity, a decline in hormone levels, chronic inflammation, muscle denervation, mitochondrial dysfunction, infiltration of fat into muscle, and insulin resistance.

Research suggests that the rate of loss of muscle strength is greater than the loss of muscle mass and plays a crucial role in healthy aging. When low muscle mass and function, including strength and physical performance, occur with aging, it is known as sarcopenia. The term “sarcopenia” originates from the Greek words “sarx,” meaning flesh, and “penia,” meaning loss.

Sarcopenia can be classified into two categories: primary sarcopenia, which is the cumulative result of various factors leading to muscle loss with aging, and secondary sarcopenia, which is caused by a specific insult, such as surgery, hospitalization, or injury. By understanding these categories, we can better diagnose and manage sarcopenia in older adults.

The trajectory of age-related muscle loss

The loss of muscle strength with age can be surprising to many people, as it can start as early as age 30. As numerous research studies have shown, the rate of decline for muscle mass with age worsens with each decade.

Age Percent loss of muscle mass/decade
50s 0.5-2%
60s 4-5%
70s 7-8%

The decline in muscle strength is more dramatic and can be 2-5 times greater than decline in muscle mass.

Age Percent loss of muscle strength/decade
50s 3-4%
60s 9-10%
70s 11-12%

A study found that there was muscle loss of between 35% and 40% occurring between the ages of 20 and 80. Additionally, studies of nursing home residents have found that sarcopenia, affects 30-40% of individuals. Mobility aids, such as canes, walkers, or wheelchairs, are commonly used by older adults, with 24% of those aged 65 years and older relying on such aids. Alarmingly, the death rate from falls is projected to rise sharply in the coming years, as shown in the graph below.

Image Credit: CDC:

Skeletal muscle mass is shown to be an independent predictor of death, highlighting its crucial effect on longevity.

These statistics don’t consider the sudden health events that can accelerate muscle loss. A rapid decline in muscle mass and health occurs with hospitalizations and illnesses. In addition to the lack of activity during hospital stays, other factors like increased levels of pro-inflammatory agents and cortisol can have a compounding effect. For older adults, this loss of muscle mass and function can lead to permanent disability or even death.

Connection between muscle health and dementia

Dementia affects more than 55 million people worldwide, and physical inactivity is one of the modifiable risk factors for the condition. There is a well-established link between low muscle mass, low physical activity, and cognitive impairment in old age.

Exercise releases myokines from the muscle, which crosses the blood-brain barrier and helps regulate BDNF, a protein that supports the survival and growth of neurons in the brain. Furthermore, the lower an individual’s muscle mass, the more significant their cognitive decline, suggesting a dose-dependent effect.

Steps to preserving muscle health and function.

Protecting your muscle mass is like increasing your savings: the greater the savings, the more comfortable you will be as you age.. While we might develop pharmacological treatments for muscle loss in the future, currently, the best way to preserve muscle function is to put in work upfront.

1. Strength training, “the medicine”

Resistance training activates our DNA to respond to stress, leading cells to produce increased muscle protein.

Initially, we may see an improvement in strength but not much muscle hypertrophy because of an increase in muscle protein breakdown. However, this slows down after about six weeks, and we start seeing an increase in muscle size.

Strength training can counteract the accumulation of fat in the muscle, improve the health of neuromuscular junctions, improve muscle quality, and reduce inflammatory markers.

People who do regular resistance training have a 20-year advantage. For example, 85-year-old weightlifters showed similar power and muscle features as 65-year-olds who did not engage in regular training in studies.

To achieve optimum improvement in muscle mass and strength, we should engage in resistance training 2-3 times per week per muscle group in addition to any aerobic exercises.

Resistance exercises that involve increasing load and speed should be done under supervision to ensure proper form and avoid injury.

2. Protein intake

Studies have shown that higher protein intake is associated with greater muscle mass and lower risk of developing frailty in older adults.

Protein intake should be individualized based on age, sex, activity level, and health status, but generally range from 1.6-2.2 grams per kilogram of body weight per day.

A systematic review and meta-analysis published in the British Journal of Nutrition in 2020 found that plant-based protein sources can be just as effective as animal-based sources for improving muscle health. It’s best to mix and match various plant-based sources of protein for optimum effect.

Consuming more than 35-50 grams of protein at one time does not provide any additional benefit for muscle growth, as excess protein is used for energy production. Therefore, it is best to spread protein intake out throughout the day rather than consuming the whole day’s amount in one sitting.

3. Supplements: Please see an excellent blog by Dr. Kaufman on this website to gain more knowledge about the safe use of supplements.

4. We all know to get good sleep and stay hydrated—more on these topics in future blog posts.

Why We Need Exercise: An Evolutionary Perspective

Why We Need Exercise: An Evolutionary Perspective

By Maya Shetty

By now, we have all heard that exercise is good for us. But why is this true? And if it’s so good for us, why is it so hard to get up and do it? The Center for Disease Control (CDC) claims we need 150 minutes of moderate exercise and 2 days of muscle strengthening exercise a week to reduce our risk of chronic disease and other adverse health outcomes. However, nearly 80% of US adults are not meeting these guidelines, and 6 in 10 have one or more preventable chronic diseases. To understand this disconnect, we need to begin by examining the evolutionary perspective of exercise – why did humans evolve to exercise in the first place?  

The first Homo Sapiens emerged around 200,000 years ago and their lives looked very different from our lives in the modern day. While we complain about having to take the escalators instead of the stairs or our food delivery taking too long, our ancient ancestors were running from predators and hunting for prey. Humans subsisted through hunting and gathering for food, and this was the primary way of life for 95% of human history. This means the majority of our evolution was spent living as nomadic hunter-gatherers. Therefore, our body and behavior is primarily adapted for this lifestyle.

An Evolutionary PerspectiveNow, you may be wondering how this translates to exercise in today’s society. Well, as hunter-gatherers, our ancestors’ main advantage was endurance. We are not the strongest or fastest animals out there, so survival was dependent on our ability to outrun our predators and prey. Evolutionarily, we are endurance athletes adapted for consistent, long bouts of physical activity. If this is the case, then why does the average American spend most of their time relatively immobile? This is because we are also adapted for inactivity and energy conservation whenever possible. Thinking again about the hunter-gatherer lifestyle, our ancestors were constantly trying to maintain their energy balance – food intake vs. energy expenditure. It made sense to exercise only when necessary for survival, and conserve energy whenever possible. In today’s society, however, this biological tendency no longer serves us, as our environment has been engineered for an extremely positive energy balance: excess food with little energy expenditure. Now we must go against our biological tendencies and make the decision to exercise, even when our body is telling us not to, in order to maintain good health. 

We can see just how much our physical activity differs from our hunter-gatherer ancestors by studying the few modern day hunter-gatherer communities. These populations are often used as models in public health due to their remarkably low rates of chronic disease and disability with age, a stark difference from modern day America. Researchers analyze the behaviors of these populations to have a better understanding of the evolutionary causes of chronic diseases – Why are they so common now vs. then? The most commonly studied population is the Hadza, a hunter-gatherer population in Tanzania. Decades of research has quantified their daily physical activity and how it changes throughout the lifetime. Most notably, the Hadza people average 15,800 steps, about 6 to 9 miles, per day. Meanwhile, Americans average less than 4,800 steps, about 2 miles, per day – about ⅓ the steps of modern hunter-gatherers. On top of this, the average American reduces the amount of steps they take per day by about half between the ages of 40 to 70. The Hadza people, on the other hand, barely change their physical activity levels with age. These behaviors have measurable effects on our physiology. By the age of 60, most Americans walk 33% slower, have less muscle mass, and their VO2max – an indicator of cardiovascular health – decreases by 25%. These functional losses are seen at a significantly lesser rate, if at all, in hunter-gatherer populations. These findings align with the theory of disuse and aging brought forth by Walter Bortz II, a Professor of Medicine at the Stanford University School of Medicine, and one of America’s most distinguished scientific experts on aging and longevity. Dr. Bortz claims the changes commonly associated with aging, such as loss of muscle mass and decreased maximum oxygen consumption (VO2max), are due to disuse with age, rather than aging itself. The differences in physical capabilities with age seen between the modern American and the Hadza people suggest our sedentary lifestyle may contribute to accelerated aging. By being sedentary, we oppose the evolutionary history encoded in our genes for periodic activity, leading to accelerated physiologic loss with age due to disuse. 

 Regular physical activity stimulates our body to allocate energy toward repair and maintenance, slowing cellular senescence and aging. It has also been seen to have dose dependent effects on the risk of several chronic conditions. 

These include:

-Cardiovascular disease and hypertension

-Type 2 diabetes




-Lung disease

-Many cancers

-Alzheimer’s disease and dementia of any type

Many theories have been suggested about how exercise is able to elicit such powerful health effects. It is widely accepted that many benefits stem from the prevention of excessive weight gain, maintenance of normal blood pressure, decreased levels of unhealthy triglycerides, increased levels of healthy lipoproteins, decreased blood sugar levels, reduced systemic inflammation, and decreased stress levels. However, how these effects come about is still debated. 

Studies have also found that regular physical activity stimulates brain growth and improves cognitive function, counteracting the loss of memory and cognition seen with age. Specifically, running has been shown to stimulate the production of neurotrophic factors, or biomolecules that support the growth and survival of neurons. Brain-derived neurotrophic factor (BDNF), for instance, strengthens neuron synapses, increases the production of new nerve cells, and promotes the growth of dendrites. BDNF expression directly increases in response to exercise and is an exciting example of how exercise attenuates cognitive loss.

The World Health Organization suggests that about 150 minutes per week of moderate exercise or 75 minutes per week of vigorous exercise reduces the risk of all-cause of mortality by ~50% in otherwise sedentary individuals (1). Aside from reducing risk of mortality, regular physical activity has been shown to improve functionality, cognition, mood, and healthspan – the amount of time spent in good health- without the functional losses of aging. Despite the extensive benefits of exercise, most of us do not routinely exercise and spend the majority of the day sedentary. Our drive to not exercise, however, is as encoded into our genes as our necessity to exercise.  As difficult as it is to find the time and energy to exercise, we as humans are genetically selected for lifelong physical activity and, because of this, regular exercise is synonymous with good health. Our world has been engineered for our convenience, not our health, and for this reason we need to make the personal decision each day to walk more, sit less, and make physical activity a regular habit. Something is better than nothing, so find something that brings you joy! Identify activities that you like and can see yourself consistently doing throughout your life. When you are short on time, taking the stairs instead of the elevator or a short walk after a stressful day can still have tremendous benefits.  Whether it be running, dancing, boxing, walking, pilates, biking, etc., just remember to find joy in it and be proud of yourself for putting in the effort. Your health will thank you later.