Physical Activity + Safety
One of the big deterrents for many considering starting an exercise program is a fear of injury or heart attack. The guidelines specifically address this issue, stating that studies in generally healthy people clearly show that there is low risk with moderate-intensity activity.
The risk of injury does increase with the total amount of physical activity, which makes sense. For example, someone who is running 40 miles per week has higher risk of injury than someone running 10 miles per week. Not surprisingly, there is also higher risk of injury in contact or collision sports such as soccer or football.
It is also important to note that those who are less fit are more likely to be injured than those who are more fit when doing the same activity. For example, cardiac events (heart attack or sudden death) are very rare during physical activity, but the risk does increase when a person suddenly becomes more active than they were previously. The greatest risk comes when an adult who is usually inactive engages in vigorous intensity activity (for example, shoveling heavy snow). People who are regularly physically active, however, have the lowest risk of cardiac events both during activity and overall. In order to minimize this risk, it’s important for someone who is deconditioned and starting to ramp up their activity to “start low and go slow.”
The bottom line is that the health benefits of physical activity far outweigh the risks of adverse events for almost everyone, and we also have to weigh the risks of being inactive, such as increased risk of chronic disease, decrepitude, and injury or heart attack when life does demand for us to suddenly exert ourselves.
Here are some ways that the guidelines suggest to minimize risk:
- Choose types of physical activity that are appropriate for current fitness level and health goals
- Increase physical activity gradually over time to meet key guidelines or health goals. “Start low and go slow” with lower intensity activities and gradually increase frequency, duration, and intensity over time. Consider one-on-one instruction when learning something new.
- Use appropriate gear and sports equipment, choose safe environments, follow rules, and make sensible choices about when, where, and how to be active.
- Consider air quality when planning to be active. Exposure to air pollution is associated with health problems including asthma attacks and cardiac events. If possible, modifying the location or timing of exercise outdoors to avoid heavy traffic and industrial sites especially during rush hour or high pollution times can improve safety. The Environmental Protection Agency Air Quality Index (AQI) provides information about when air conditions are unhealthy that can be accessed here.
- And as a reminder, those who have a chronic health condition, symptoms, or are pregnant, should be under the care of a healthcare provider and consult with their health care provider or trainer about types and amounts of activity that are appropriate for them.
Physical Activity and Our Health
Now that we know the guidelines and some parameters for implementing physical activity safely, we’ll review what we know about how physical activity impacts our health.
Most striking is the impact of physical activity on all-cause mortality, or death from any cause. To put some numbers to this, it’s estimated that people who are active 150 minutes/week have a 33% lower risk of death from all causes than those who are not physically active.
The graph below compares amount of physical activity per week and mortality. As you can see, the highest mortality (or risk of dying) is over on the top left, when someone is not physically active at all. From there, there is a pretty steep drop off - where going from no physical activity to just small amounts of physical activity results in a large reduction in risk of dying. Most of the benefit of physical activity on mortality risk is achieved by the time you get to 150-300 minutes/week, which is how the guidelines were derived. However, there does seem to be additional benefit and no increased risk of mortality even at very high levels of physical activity (3-5x the amount recommended in the guidelines).
Aside from decreased risk of death, regular physical activity has many other specific health benefits which are outlined in the table below:
Cardiorespiratory + Metabolic Health
Cardiorespiratory and metabolic health are the areas that have been most heavily researched and where the benefits of regular physical activity are abundantly clear. Physical activity strongly reduces both the risk of developing and dying from cardiovascular disease including heart attack, stroke, and heart failure.
Exercise also reduces elevated blood pressure, an effect that can be observed immediately after just one bout of physical activity. Regular physical activity can also reduce the risk of developing high blood pressure in the future.
Regular physical activity also reduces the risk of developing type 2 diabetes. Insulin sensitivity can improve with just a single bout of physical activity. Physical activity also helps to control blood glucose in people who already have type 2 diabetes, and reduces the progression of the disease.
Lower triglycerides and higher HDL are also observed in those who exercise regularly. Physical activity can also help with weight gain, but it’s important to note that a lot of the benefits of exercise are independent of weight. So, even if someone is not losing weight while exercising, they are still experiencing a lot of health benefits.
Bone and Musculoskeletal Health
Exercise also plays a big role in the health of our muscles and bones. We know muscle strengthening exercises help to preserve or increase muscle mass, strength, and power and can also improve muscular strength in people with conditions where the musculature is affected such as stroke, MS, cerebral palsy, and spinal cord injury.
When it comes to bones, regular exercise helps us to build strong bones as we are growing up, and it also helps to reduce the decline in bone density that is often seen with aging. Improved symptoms of osteoarthritis and other bone conditions, pain management, function, and quality of life are also seen in those who are physically active. In particular, having arthritis can often be a deterrent to doing exercise, but regular physical activity is associated with decreased pain, improved physical function, and improved health-related quality of life in those with osteoarthritis, and being active does not seem to make the arthritis progress any more quickly than it would otherwise.
Functional Ability and Fall Prevention
Physical activity is critical for functionality and the prevention of falls in older adults. Physical activity can prevent or delay the onset of functional limitations that necessitate the need for assisted living or 24/7 care in a nursing home.
Physical activity also reduces the risk of falling which can result in injuries that dramatically change one’s quality of life. Hip fractures are one example of this. An all-too-common story is an elder who falls and breaks their hip after which they never return to the same baseline, end up needing support for their activities of daily living, and continue to experience a decline in health until the end of life.
For those at risk for these kinds of injuries, multi-component physical activity programs including muscle strengthening, balance, gait and coordination, and moderate-intensity activities such as walking are most successful at reducing falls and injuries. This type of exercise is also beneficial for recovery of injuries such as hip fractures as well as neurological conditions such as Parkinson’s Disease and stroke.
The positive benefits of physical activity are clear, and this is an exciting and continually emerging area of research.
Some of the benefits of exercise on the brain are immediate, after just one bout of exercise. These include: reduced anxiety, improved sleep, and improvements in some aspects of cognitive function such as performance on academic achievement tests, executive function, processing speed, and memory.
Regular physical activity over the course of days to weeks is also associated with the following improvements: long term anxiety, deep sleep, sleep quality, sleep efficiency, and daytime sleepiness, decreased use of medication to facilitate sleep, aspects of executive function such as the ability to plan and organize, monitor, inhibit or facilitate behaviors, initiate tasks, and control emotions, reduced risk of dementia, improved quality of life, and reduced depression.
Physically active adults have a significantly lower risk of developing several common types of cancer including:
Benefits are also seen in breast, colorectal, and prostate cancer cancer survivors with regard to quality of life, and the risk of dying from their cancer as well as all other causes.
Pregnancy + Postpartum
Finally, with regard to women during the pregnancy and postpartum periods, physical activity is generally safe and reduces risk of excessive weight gain and gestational diabetes during pregnancy. It increases cardiorespiratory fitness without increasing risk of negative birth outcomes such as low birth weight, preterm delivery, or early pregnancy loss. In the postpartum period, physical activity decreases symptoms of postpartum depression and can improve the return to pre-pregnancy weight.
Risks of Sedentary Behavior
Now that we’ve reviewed all the wonderful positive impacts of exercise on our health, we’ll highlight the increased risk that comes from not being physically active, or from sedentary behavior.
We’ve all heard the phrase “sitting is the new smoking” by now, and it’s well deserved - sedentary behavior poses a tremendous health risk.
What does sedentary behavior actually mean? Sedentary behavior includes waking behavior with low energy expenditure, in a sitting, reclining or lying position, which may include TV or other screen time.
The National Health and Nutrition Examination Survey estimates that children and adults in the US spend 7.7 hours per day sedentary. According to the study, that’s more than half of the time they are awake! The prevalence of sedentary professions has increased by 20% in the United States between 1960 and 2008, with a simultaneous decline of more “physically active professions.”3 This may explain, in part, why we are now facing such an epidemic of sedentarism and chronic disease.
More time spent in sedentary behavior increases the risk of all-cause mortality, cardiovascular disease mortality, cardiovascular disease, type 2 diabetes, and cancer of the colon, endometrium, and lung.
A large 2016 meta-analysis study which pooled 16 studies looking at over 1 million people demonstrated that increased daily sitting time and decreased moderate-vigorous physical activity increased all-cause mortality risk.4 The heatmap above used data from this study to plot all-cause mortality risk based on both daily sitting time and the amount of moderate- to vigorous- physical activity.
From all of this data, it is clear that two different approaches are both necessary to decrease all-cause mortality risk: 1) increasing the amount of moderate- to vigorous- physical activity done per week and 2) reducing the time spent sitting (replace with light-intensity activity). Two ways we personally like to do the latter are using standing desks, and the Pomodoro Technique as a way to take regular breaks and move around.
Comparison of Exercise and Pharmaceuticals
Next, we’ll review the impact of exercise relative to pharmaceutical drug interventions we have for certain chronic diseases. When making such comparisons, it is important to note that exercise does not benefit just the specific condition the drug is treating and what is being studied. As we’ve reviewed above, exercise has a wide range of positive side effects from improved mood, to decreased cancer risk, to decreased frailty and fall risk. So even if exercise is equally or even slightly less effective than a pharmaceutical drug (that comes with its own unwanted side effects), many people may still opt to incorporate exercise if given the choice.
A 2015 study that looked at 16 meta-analyses including over 305 randomized controlled trials with over 300,000 participants found that physical activity was more effective than drug interventions among patients with stroke.5 The drug interventions they looked at included antiplatelet drugs such as aspirin or plavix and anticoagulants such as coumadin. Additionally, they found no difference in mortality outcomes between exercise and drug interventions for secondary prevention of heart disease (i.e. trying to prevent cardiac death after already having been diagnosed with heart disease), or prediabetes.
Finally, a separate review of randomized controlled trials comparing exercise to antidepressants showed that exercise and antidepressants were equally effective for depression.6
The Mechanisms: How Physical Activity Impacts Our Health7
Here, we will review 3 main mechanisms by which exercise improves our health:
- Optimizing the stress response
- Reducing inflammation
- Enhancing brain health
A Review of the Stress Response
We’ve talked about the stress response in many previous episodes, but essentially it is composed of two different systems:
- The Hypothalamic-Pituitary-Adrenal (HPA) Axis, which releases glucocorticoids including cortisol
- The Autonomic Nervous System (ANS), which includes the sympathetic nervous system that releases chemicals like epinephrine (adrenaline) and norepinephrine
Activating these systems in response to an acute stressor (such as getting chased by a tiger, or slamming on your breaks at the last minute to nearly miss a car accident) then coordinates the response of other systems (cardiovascular, musculoskeletal, GI, immune, nervous) in a fight-or-flight response that includes mobilization of energy or glucose, increases in heart rate and blood pressure, enhanced cognitive processes such as alertness, arousal, vigilance, and attention, and a coordinated inflammatory response to prepare for potential injuries or infections.
However, chronic long-term activation of this fight or flight response results in persistent activation of these systems, which can lead to chronic systemic inflammation and a whole host of chronic health conditions.
Optimizing the Stress Response
Acute exercise activates the stress response in a dose-dependent manner (that means higher intensity or longer duration exercise results in a more robust stress response). This may seem counterintuitive, however, over time this can be a good thing.
It turns out that although exercise acutely increases the stress response, repeated, intermittent exposures to exercise, with enough time to recover in between, can lead to physiological “stress training”, meaning we develop a more optimized response when we encounter exercise or other stressors in the future.
This is an example of the concept of hormesis, which is the notion that low levels of cellular stress (whether from exercise, toxins, temperature changes, or other factors) stimulate or upregulate existing cellular and molecular pathways that improve the ability of cells and organisms to withstand greater stresses.
An untrained person initially mounts a dramatic stress response to exercise, but after training, the stress response to the same physical stimulus is lower. Not only is the response to physical stress lower, but regular activity seems to provide protection against mental and/or psychological stressors as well. Regular physical activity results in greater control of the parasympathetic system (the “rest and digest” part of the ANS that counters the “fight or flight” effects of the sympathetic nervous system). This is why those who engage in regular activity are also found to have lower heart rate and blood pressure readings at rest. Additionally, higher physical fitness is also associated with a more optimized immune response.
In addition to optimizing the stress response, exercise also plays a role in reducing the chronic systemic inflammation that is seen in states of metabolic dysfunction and chronic disease. For example, inflammatory biomarkers such as C-reactive protein (CRP) are lower in those who engage in regular physical activity compared to those who are inactive. Regular exercise has been shown to reduce brain inflammation in response to insults such as stroke or infection.
This reduction in inflammation could be at least in part due to a reduction in visceral fat mass, which we know releases many pro-inflammatory chemicals, but there also seems to be an anti-inflammatory effect separate from the reduction in fat mass that may come with regular activity.
Interestingly, we know that a specific chemical called IL-6, when released from contracting skeletal muscle promotes an anti-inflammatory environment. More IL-6 is released with increased intensity and duration of exercise. Although IL-6 has a proinflammatory effect when released from other tissues such as adipose tissue, when released from skeletal muscle it has been shown to have anti-inflammatory effects.
Enhancing Brain Health
A final mechanism by which exercise improves our health is by enhancing brain health. Chronic stress with persistent cortisol exposure has detrimental effects on brain including: reduced volumes of certain brain regions such as the hippocampus and prefrontal cortex, decreased expression and signalling of neurotrophic factors (factors that improve cell growth, survival, and repair), reduced generation of new neurons and their supporting cells called glial cells, depression, and impaired cognitive function.
Regular exercise, on the other hand, has been shown to enhance positive mood, decrease depression and anxiety, and increase cognitive function. This occurs by two major mechanisms:
- Structural: Regular exercise results in increased neurogenesis, synaptogenesis, gliogenesis, angiogenesis. This means increased production of brain cells, more connections between those cells, increased surrounding support cells, and more blood vessels to bring nutrients and take away waste from the brain cells as they do their job. Structural brain changes seen with regular exercise include: increased grey matter volume and white matter integrity (especially in the prefrontal cortex and hippocampus), and decreased age-related hippocampal volume loss.
- Cellular and Molecular: Regular physical activity results in increased expression of growth factors and neurotransmitters, which results in improved function and communication between neurons.
Together both of these mechanisms help to enhance neuroplasticity, or the ability of the brain to learn and make new connections between neurons, and may be able to reduce or reverse some of the detrimental effects of chronic stress on the brain.
Brain-derived neurotrophic factor (BDNF) is one of the most important and widely studied growth factors when it comes to the impact of exercise. BDNF supports the survival of existing neurons and promotes the growth of new neurons and connections. Low levels of BDNF are found in many chronic disease states and metabolic conditions associated with insulin resistance including neurodegenerative diseases like Alzheimers, major depression, impaired cognitive function, cardiovascular disease, type 2 diabetes, and obesity. Enhanced BDNF levels are associated with improved metabolism and cardiovascular function, and decreased risk of Alzheimer’s. BDNF levels are downregulated by chronic stress and inflammation, but exercise has been shown to significantly increase BDNF production in the brain, which then circulates to the rest of the body.8
In summary, a great majority of our US population is not getting enough physical activity to substantially benefit their health. The ways that increasing physical activity and decreasing sedentary time can improve our health are numerous, and we reviewed the most recent guidelines for Americans to reap these benefits. Regular exercise can have similar effects to pharmaceutical drugs for some common conditions like stroke, heart disease, prediabetes, and depression. Exercise exerts its health benefits through three major mechanisms: optimizing the stress response, reducing inflammation, and enhancing brain health.
When it comes to helping a friend or family member get started with exercise, interventions that are based in behavior change theory are usually most successful. Some that we have found most useful are the stages of behavior change, motivational interviewing, and solution focused therapy. Generally, community or peer support is helpful for creating sustained change. Technology can provide feedback or remote coaching and guidance to someone starting a new program. Most importantly, we find that helping someone to tie their physical activity goals to their values and what’s most important to them in life is the key to finding long term success.
We also recognize that we have a lot of work to do to improve the ability of our population to be more active on a community level. Working with our communities to make doing physical activity a safe and easy choice is something we can all strive to do.
Ep 132 - Healing Through Functional Movement with Dr. Amy West
Ep 139 - Stress: The Elephant in the Room with Dr. George Slavich
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Disclaimer: This podcast is for general information only, and does not provide medical advice. We recommend that you seek assistance from your personal physician for any health conditions or concerns.