“Take care of your body. It’s the only place you have to live in.”
Jim Rohn
Moving your body is necessary to lengthen both lifespan and healthspan (What you should know about Longevity: Living a Longer, Healthier Life). Regular exercise is a critical component of primary prevention because it reduces the risk of many chronic diseases. Despite general knowledge and agreement that regular physical activity is good for health, according to the CDC more than 60% of Americans don’t follow current recommendations. Worse yet, more than 15% get no physical activity at all.
Primary prevention encompasses any intervention put into place before disease or injury happens. Examples of primary prevention include seat belts, bike helmets, vaccinations, and quitting smoking. Primary prevention also includes physical activity, like strength training to improve bone density and balance exercises to reduce falls. Finding motivation for primary prevention can be hard since the very definition implies that you feel fine – you have no symptoms but are just hoping to prevent future ones. Incentives are especially lacking when the activity requires effort, like weight training. After your mid-30s, however, you lose a pound or two a year of lean mass (particularly muscles) so primary prevention is vital. Loss of muscle is associated with loss of function and, ultimately, loss of longevity. The correlation is so strong, in fact, that hand grip is an excellent predictor of longevity.
Osteoporosis may seem like a concern for midlife. I learned early in my medical career, however, that a hip fracture isn’t just a painful inconvenience (Life and Death: Mothering and Doctoring). A hip fracture can ruin a life or end it. In fact, up to 1/4 of people suffering one will die within 3-6 months and 1/3 will die over the first year. Those who survive remain at higher risk of death than the general population for nearly ten years afterward. Of the surviving, only about 60% recover their previous function (are able to continue performing activities of daily living) while 1/4 of survivors will require constant nursing care. In other words, the consequence of a misstep in someone with fragile bones is often death or relegation to a nursing home. Strength training is a commitment to your future self to prevent this tragic ending.
Your muscles are attached by tendons to your bones. When you lift a weight, do a push-up, or engage your muscles in some way you send a message to your bones to “get stronger here.” Subjecting bones to appropriate stress (as in strength training) causes the formation of new bone. Bone cells (osteocytes) signal the remodeling of bone to make it better suited to withstand the stressor. Overloading muscles causes micro-injuries in bone that activate your osteocytes to create new bone. The opposite is also true. When bone isn’t subjected to stress or strain it will adapt to this too, by ridding itself of extra mass.
Another longevity benefit of strength training is its effect on metabolism. When trying to lose weight, it’s common to focus exclusively on cardiovascular activity (“burning calories”), neglecting the positive metabolism boost that weight training provides. Because muscles require a lot of energy, stronger muscles result in an increase in basal metabolism – calories burned at rest to maintain body function. Muscles are composed of different types of fibers – some for running a marathon and others for lifting heavy things. Cardiovascular activity (endurance) requires one fiber type while weight training (strength and power) uses another. Getting out of a chair or lifting a heavy bag to overhead storage on a plane requires this second type of fiber. Unless you are actively maintaining your muscle mass through strength training, with age these muscle fibers become smaller and lose their effectiveness. The result is an inability to perform tasks involving quick movement and strength. Once you can no longer perform these daily activities of life, you risk requiring assisted living.
Secondary prevention involves screening to identify diseases in their earliest stages, often before any symptoms develop. This includes mammograms, colonoscopies, and blood work measuring cholesterol and blood sugar. According to the CDC 1/3 of American adults have prediabetes and 80% are unaware of the diagnosis. It is well established that diabetes increases the risk of heart disease and stroke, making it crucial to find and treat prediabetes. Not surprisingly, exercise lowers the rise in blood sugar after meals (glucose is shunted to provide energy for muscles). A small study published this May in Medicine and Science in Sports and Exercise (Breaking Up Prolonged Sitting to Improve Cardiometabolic Risk: Dose-Response Analysis of a Randomized Crossover Trial) showed that interrupting long periods of time sitting (every 30 minutes) with light intensity activity (like walking) lowered blood sugar and blood pressure. This is good news for those who have sedentary jobs. Stepping away from your desk for a short period of time can help with diabetes and hypertension. While 5 minutes of activity was necessary for improved glycemic responses, researchers believe even less time may be sufficient to lower blood pressure.
Because physical fitness is such an important indicator of cardiovascular health, the American Heart Association recommends aerobic capacity be evaluated as part of routine doctor encounters, just like blood pressure. Currently, cardiorespiratory fitness (CRF) is the only major risk factor that is not routinely assessed in clinical practice. For an excellent overview of the AHA statement, read this: Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign. CRP measurement provides doctors with an opportunity to encourage lifestyle-based strategies to reduce cardiovascular disease – the number one killer of Americans. While heart disease has traditionally been thought of as a disease of men, one in five women dies of cardiovascular disease. Even more shocking, over 1/4 of women who have a heart attack will die within a year. In addition to heart health, low CRF is associated with a higher rate of diabetes and metabolic syndrome whereas high CRF is associated with a lower risk of lung, breast, and gastrointestinal cancers.
Why is CRF such an important indicator of overall body health? CRF reflects the body’s ability to transport oxygen to the mitochondria (powerhouses of the cell) to perform work. CRF depends on multiple factors including lung function, heart pumping capacity (cardiac output), and the ability of blood vessels to accommodate and transport oxygen. Cardiac output is a measure of the amount of blood the heart pumps out each minute, which is determined by heart rate and stroke volume (the amount of blood pumped with each beat). Both of these increase during exercise, resulting in an increase in cardiac output to meet higher oxygen demand.
CRF is also dependent on the ability of muscle cells to receive and use oxygen and to communicate these demands to the cardiovascular control center. When you exercise, your blood flow increases. This ultimately leads to the development of more capillaries, more myoglobin (to transport oxygen in the muscles to mitochondria), and more and larger mitochondria. The result: your body extracts oxygen from your blood more efficiently. In other words, CRF is directly related to the integral function of multiple systems – lungs, heart, vasculature, and muscles. This makes it an excellent indicator of total body health.
CRF can be determined by measuring VO2 max, or maximal oxygen consumption. To find out your VO2 max, you would exercise to full capacity while wearing a mask that measures your oxygen use. The higher the VO2 max (oxygen consumed over one minute expressed in mL/kg/min), the more efficient your heart is at oxygenating your organs and tissues. An increase in aerobic capacity (as measured by VO2 max) improves heart, vascular, and metabolic function leading to lower blood pressure, blood sugar, and cardiovascular morbidity and mortality.
While VO2 max is a direct way to determine CRF, it isn’t often practical to measure this in a primary care setting. However, because low CRF is as strong a predictor of mortality as smoking, hypertension, hyperlipidemia, and diabetes, it may be worthwhile to find this out on your own (through an exercise physiologist or other qualified provider). If this isn’t possible, CRF can be estimated by peak work rate on a treadmill or cycle ergometer or through a submaximal exercise test, especially if resources are limited.
The good news for sedentary people is that substantial health gains can be achieved with small improvements in CRF, including a 10-30% lower adverse cardiovascular event rate. Endurance exercise causes adaptations in your body that increase CRF, like increased stroke volume and improved oxygen extraction by trained muscles. Therefore, most people can improve their CRF by regularly performing rhythmic contractions of their large muscle groups for an extended time period at a moderate or vigorous intensity (more on the “How” of physical activity in part 2). Those who will receive the most benefit are those who are currently the least active.
It is well established that exercise helps our hearts, but medical professionals also recognize that heart health = brain health. In fact, physical activity may be the single most important lifestyle intervention you can do to keep your brain healthy. Exercise is essential in memory, learning, and mood. When we exercise, our bodies produce brain-derived neurotrophic factor (BDNF) which improves neuroplasticity – the brain’s ability to create and organize connections between brain cells. Not surprisingly, there’s a correlation between circulating BDNF and a lower risk of Alzheimer’s disease, causing dementia experts to prioritize physical activity in preventative efforts. In addition to increasing BDNF, aerobic exercise also appears to reduce inflammatory markers in older adults (such as CRP, IL-6, and TNF) which are related to cognitive decline. Aging also impacts the ability to cope with stress. Chronic stress causes overactivity of the “fight or flight” system, which can have important implications for blood sugar (cortisol increases blood sugar). Exercise downgrades the stress response through multiple mechanisms. Check out this 2020 Article in the Journal of Aging Research for more information: Effects of Exercise on Cognitive Performance in Older Adults.
Finally, tertiary prevention is the management of chronic disease aimed at slowing or stopping progression. This can include medication, physical therapy, and screening for complications. While there is some overlap between secondary and tertiary prevention, clearly the sooner preventative measures are instituted to improve health (ideally before disease develops), the more impact the intervention will have. Quite simply, start today.
Now that you understand the importance of exercise, where do you start?
(Hint: get outside with your loved ones)
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