By Coach Matt Slater
Before any discussion of the potential negative side effects of high-intensity or high-volume exercise on the heart it is important to understand that lack of activity carries significant risk as well. Cardiovascular disease (CVD) or heart disease is the number one cause of mortality in the United States and is responsible for approximately one in four deaths. There is a lot of heart disease out there.
Coronary artery disease (CAD) also known as atherosclerosis or “thickened arteries” is the most common form of heart disease, killing 400,000 Americans in 2017. About 18.2 million adults age 20 and older have CAD (~ 6.7%) and 20% of deaths from CAD occur in those under 65 years old. Atrial fibrillation (aFib) is also common; approximately 2% of Americans under 65 have atrial fibrillation and 9% of Americans over 65 have atrial fibrillation. That’s a lot (millions) of people. Atrial fibrillation is clearly not confined to endurance athletes.
Atrial fibrillation is a specific abnormal heart rhythm of the upper chambers of the heart (the atria). Instead of beating regularly and in synchrony with the lower chambers of the heart the atria beat rapidly and irregularly. Atrial fibrillation or “Afib” comes in several forms; Paroxysmal which is on and off and is self-limiting, Persistent where the individual stays in atrial fibrillation until they are converted with either a shock or medication (“cardioverted”) and Permanent where people are, well, permanently in atrial fibrillation.
The major concerns with atrial fibrillation are stroke risk and cardiac dysfunction (poor heart performance). The stroke risk is due to reduced blood flow in the atria and the formation of blood clots which can be ejected into the circulation. The risk of cardiac dysfunction is due to either high heart rates, disorganized pumping between the upper and lower chamber of the heart, or both resulting in reduced cardiac function. Prolonged elevated heart rates with atrial fibrillation can result in permanent heart damage (cardiomyopathy).
Exercise alone does not protect against CAD. The high prevalence of coronary artery disease in our country means that fit individuals, even those without traditional risk factors (smoking, family history, high cholesterol), may still have coronary artery disease.
The GOOD: exercise will make you healthier and live longer
Although we cannot change our family history or genetics, we can modify several of the risk factors associated with cardiovascular disease. Improving the quality and quantity of our sleep, proper nutrition, and regular exercise have been shown to slow the development of coronary artery disease and prolong life. The challenge is determining the correct dose of these interventions. Today we will focus on exercise; too little versus too much and the relationship between exercise and atrial fibrillation.
Before starting an exercise or training program It is reasonable to have a formal assessment of cardiovascular risk. Consultation with a primary care physician or cardiologist prior to embarking on a training plan is appropriate. This is true for individuals at any stage of life. Even high school athletes and NBA players are being screened for cardiovascular disease.
The BAD: There really is a relationship between exercise and increased atrial fibrillation
Recently there has been growing concern that high levels of exercise can increase the risk of atrial fibrillation. Books with titles such as The Haywire Heart: How too much exercise can kill you and what you can do to protect your heart have raised concerns. It’s hard to imagine how a book that contains the “kill you” in the title would fail to do so. Even Wikipedia states that atrial fibrillation is associated with high levels of endurance training.
I will discuss the information that we have currently with regard to atrial fibrillation and put this into a context that allows individuals to make decisions regarding exercise choices. The perfect test or algorithm to determine the likelihood for each individual to develop atrial fibrillation in response to varying exercise volumes and intensities does not exist. Each person is different, but we can make some generalizations and use them to help guide or decision making.
The UGLY: There is a lot of information out there
The risk of atrial fibrillation associated with training at high workloads over many years needs to be put in the context of other risk factors (hypertension, obesity, alcohol consumption obstructive sleep apnea, smoking, bad lipid profile) that are also associated with higher rates of atrial fibrillation. This also needs to be balanced with the health benefits of exercise and the less tangible but equally important things we each derive from exercise, competition, and being physically fit.
Studies have demonstrated reduced rates of atrial fibrillation in people who exercise compared to those who are sedentary. A study by Mohanty in 2016 https://onlinelibrary.wiley.com/doi/abs/10.1111/jce.13023 demonstrated a 250% increased rate of atrial fibrillation in sedentary individuals as compared with those who exercised. In the subgroup who participated in “vigorous” activity, there was 330% increase in atrial fibrillation although this effect was confined to males. Women are often underrepresented (or excluded) in many studies. The differing response of males and females to exercise is a topic that I plan to explore in a future blog.
Some studies have reported that the effect of training on the development of atrial fibrillation appears to be associated with total years of training, not intensity (https://www.ncbi.nlm.nih.gov/pubmed/31340437) One study found that there appeared to be a threshold at about 2,000 hours of training. (https://www.ncbi.nlm.nih.gov/pubmed/26333377)
Additionally, it is important to understand that less traditional risk factors such as working long hours (>55/week) (Kivimaki 2017), having children, being male, and watching television “very often” (Yasuhiko, 2018) and lack of sleep (Christensen 2018) raise your risk of developing atrial fibrillation. If you are a male who has worked too much, lacks sleep, likes to drink wine and ride their bike really hard you could be in trouble…Oh wait, that’s me…!!
Moderate exercise lowers the rate of atrial fibrillation. Exercise is also effective at preventing coronary artery disease and the development of other illnesses. However, the rate of atrial fibrillation is higher for endurance athletes exposed to large volumes of high intensity training over significant periods of time.
In summary, the data show that the benefits of exercise outweigh the risks for the vast majority of individuals. The precise relationship between atrial fibrillation and exercise dose, intensity, and cumulative lifetime volume of exercise is not yet clearly defined. A long-term training plan must integrate all of these components and incorporate each individual’s goals.
Coach Matt Slater is now taking clients.
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