Prime the Pump

“It always seems impossible until it is done. “ - Nelson Mandela

The heart is an exquisitely designed electro-mechanical pump connected to an elaborate system of tubes—the blood vessels--that branch out and extend throughout the entire body. At least 100,000 times a day, the heart pumps about 5 L of blood through thousands of miles of blood vessels. Its pumping action must generate enough force to supply all our tissues—from the smallest ligament to the largest organ--with the oxygen needed for them to function properly. With its finely tuned electrical currents and efficient mechanical expansions and contractions, the heart works remarkably well at keeping our body humming along seamlessly, working tirelessly to maintain a comfortable state of physiological equilibrium.

Humans would never have made it far through history if the heart’s only function was to maintain the status quo. Rather, it is the heart’s inherent adaptability and resilience that gave us an evolutionary edge and helped us thrive in a variety of climates, terrains, and circumstances. For millions of years our ancestors had to walk the equivalent of five to nine miles every day just to survive. Plus, their circumstances were always changing—sometimes they had to carry loads, push or pull things, rapidly change their pace, break into a run or even a sprint. Our cardiovascular systems evolved to adapt to the changing demands of our environment, providing a continuous supply of oxygen even when our heart was working well above resting levels. The heart’s adaptability gave us an incredible capacity for endurance not found in other species. Eventually our physiology became programmed to get stronger when exposed to repeated bouts of moderate to hard exercise; we have genes that are responsible for the maintenance and repair of our bodies that become active only when we are exposed to the stress of being physically active.

We live in a world in which physical activity is no longer a necessity for staying alive; we sit for hours in chairs, stare at screens, hold steering wheels, or click buttons. Our clever brains have designed lots of ways to make our lives much easier than our ancestors but in doing so, we’ve created an environmental mismatch for our ancient physiology that is wired for movement. Physical activity is critical for the health of the cardiovascular system because it never evolved to get stronger spontaneously, in the absence of demand. Since inactivity makes us vulnerable to cardiovascular disease, the sedentary environments we created pave a path straight to a host of heart health issues. This is why, in the past 120 years, even with advancements in medical treatments, heart disease is still the leading cause of disease and disability for adults in modernized societies.

Although the study of how exercise impacts the body is a relatively new field, we now know that exposing the heart to the stress of physical activity is essential for our health. There is a firm belief in the medical community that exercise is medicine but, given the heart’s capacity for resilience and adaptability, the prescription can be a bit tricky. The length, intensity, and type of exercise each have an impact over the type of improvements that occur. For someone who is mainly sedentary, any physical activity that is sustained over time will help to improve the health of the heart—even a 30-minute stroll can stimulate improvements in heart health. But the heart is designed to be challenged, so more significant changes happen only as workloads get progressively heavier. Since our cardiovascular systems are incredibly adaptable, the reward for our hard work is always more work; exercise may be medicine, but we need to keep tweaking the prescription and adjusting the dose so that the heart continues to grow stronger and more responsive.

What is technically referred to as aerobic exercise—aka, “cardio”—is the most widely accepted form of exercise prescribed for heart health. Aerobic exercise is any rhythmic movement that uses the large muscles of the body and elevates the heart rate between 50 to 70 percent above resting levels. Measuring heart rate may seem technical but is easy enough to estimate subjectively by using the breath and gauging how difficult it is to talk. At lower levels of aerobic exercise, the rate of breathing increases to a point at which it is fast enough to make singing impossible, but not so hard that a person can’t talk. As the workload increases, the breathing rate gets faster, making talking more difficult to manage. At 65 – 70 percent, a conversation is possible, but you’ll need to take a breath every few words or phrases. The general rule for aerobic exercise is that the lower the workload, the longer the exercise session can last; as intensity increases, the length of the workout decreases.

During aerobic exercise, the heart is required to deliver oxygen to the working muscles at a faster rate than at rest. This increased demand stimulates the chambers of the heart to become more spacious and elastic. As the chambers increase their capacity to hold more blood, the heart responds by contracting more strongly, pushing more oxygenated blood into the blood vessels where it is delivered to the working muscles. The increased output stimulates the development of additional blood vessels to help supply more oxygen throughout the body. As the heart gets stronger and pumps blood more forcefully, blood vessels become more pliable and capable of expanding to meet the increased blood supply. Just like traffic congestion is eased when highways are designed to meet capacity, these changes help to lower our blood pressure and improve the resiliency of the heart. They also have significant downstream effects, especially in our blood chemistry, as good cholesterol (HDL) increases, while bad cholesterol (LDL) and circulating fats (triglycerides) decrease.

Exercise may be medicinal for the heart, but only when it is taken as prescribed. Whereas our ancestors had to respond to their immediate environment—they had to sprint to escape danger, run to kill prey, and move for hours just to survive. Life provided a steady dose of medicine. Now it is we who are responsible for administering the proper dose, but that is hard to do, especially when we are in the habit of sitting. The brain is the main source of resistance to exercise, as it strives to keep all our systems in a steady state of equilibrium. Exercise is a stressor so the brain does whatever it can to keep us in our comfort zone. It isn’t until we get into the habit of being physically active that the brain recognizes its benefits and stops fighting against our need to move.

For aerobic exercise to be beneficial, it needs to be sufficiently challenging for our level of fitness. Every dose of exercise helps the heart to grow stronger, so the bar for the perfect dose is always shifting. When it comes to physical activity, we are notorious for overestimating how hard we are working, most likely because we focus on inaccurate estimations of how many calories are burned rather than our breathing rate. Studies have found that subjective measures of exertion can be surprisingly accurate, but this method has fallen out of favor with our reliance on wearables such as Fitbit and Apple watches. We most likely would improve our fitness levels if we focused on how hard we were breathing rather than numbers on a watch.

Many of us are creatures of habit, so once we get into the groove of doing cardio, we tend to gravitate toward doing the same thing, for the same amount of time, the same days of the week. Any exercise is good for the heart, but studies have found that variety is an important ingredient in the overall prescription for heart health. If possible, it is helpful to change the types of cardio we engage in to avoid the musculoskeletal injuries that result from overuse. If our modes of exercise are limited, we can find variety in changing the incline and speed. We can even get variety in a simple walk by changing the pace, the route, or the number of hills climbed.

Recent studies have shown that intensity is particularly beneficial for the heart. Important changes take place in cardiac muscle when the heart is repeatedly exposed to short bursts—30 to 60 seconds--of very intense exercise that pushes effort levels into very uncomfortable zones, typically 80 to 90 percent of our heart rate maximum. At this high level of effort, a person cannot talk, is struggling to breathe, and must focus completely on the work. The biggest benefit of this type of training is that, over time, the heart becomes more resilient, able to recover faster from heavy loads. Some have suggested that short bursts of hard work mimic the environmental stressors faced by our ancestors, making them more in sync with our biology.

It is easy to get bogged down in technical details when it comes to cardio—what type is best, how long, how often, and so on. To avoid confusion, it is helpful to follow some simple guidelines. First, recognize that it is hard to start and even harder to keep going. Exercise is stressful and can be uncomfortable. Expect to face resistance and know that we are all good at talking ourselves out of working hard. Even the most seasoned marathon runner cringes at the thought of a run on a raw, rainy day. Plus, when the exercise session starts, we experience what is known as an oxygen deficit. It takes time when we first start to exercise—sometimes as long as 15 minutes--for the cardiovascular system to ramp up and start delivering sufficient oxygen to the muscles. Until then, the muscles may feel heavy, and our breathing painfully labored. Also, the “feel good” brain chemicals associated with exercising—dopamine, serotonin, and endorphins—can take as long as 20 to 30 minutes to be released when we are new to exercise, making it hard to find motivation to continue. Just know that, regardless of your fitness level, all exercisers feel sluggish and uncomfortable at the starting line; with training, that feeling is less intense and does not last as long.

Another important guideline has to do with exercise volume and avoiding injury. It takes about six weeks for the heart to show significant improvements in capacity; it takes 12 to 18 weeks for the musculoskeletal system to adjust to the demands of a particular mode of exercise. The most common way to sideline your exercise routine is doing too much, too fast. This is common in new runners, who may feel great at the end of a three-mile run, so they start to quickly ramp up mileage before the muscles and bones have time to adjust. The result is an injury such as shin splints, torn hamstrings, or back pain. Be sure to meet your body where it is rather than try to push it to do more than it is capable of doing.

Perhaps one of the most important guidelines is that, to keep our hearts healthy, our exercise should mirror life. Rarely are we faced with the same stressors every day, at the same intensity, for the same length of time. What makes an event stressful is that it is unexpected, throwing us into a state of uncertainty. Our ancestors faced this unpredictability every day. One day they walked three miles to find food, another day it was nine miles, and sprinting was frequently thrown into the mix at unexpected times. These are the kinds of environmental stressors our ancestors encountered that helped to build the heart’s resiliency and adaptability. Just as with life, predictability offers comfort and ease, but having the rug pulled out from under us is the stuff that makes us—and the heart—stronger, healthier, and resilient.