Cardiovascular Workouts: Hazards and Risks

Are you well-versed in the benefits and harms of aerobic exercise volume? How often to do cardiovascular workouts? How long should cardio workouts be?

Meet and greet – a grandiose recent review of the scientific literature (51 papers, list attached) on the dos and don’ts of aerobic exercise volume.

Why and When Cardiovascular Workouts Can Be Dangerous

Almost everyone knows that physical activity is important. A wealth of scientific evidence supports the therapeutic effects of exercise on quality of life, cardiovascular (CV) health, and longevity.

At the same time, many people mistakenly believe that the more, the better. Excessive training volume of cardio loads can negatively affect the health of the CVS. Ultramarathons can cause myocardial damage, as evidenced by elevated levels of troponin and brain natriuretic peptide.

In addition, sudden cardiac arrest occurs more frequently in marathons and triathlons than in shorter-distance competitions. Elderly marathon runners often have abnormal remodeling (structural changes) of the heart with an increased risk of myocardial fibrosis and ischemic calcification.

Chronic excessive cardiovascular workouts are associated with an increased risk of atrial fibrillation (AF).

How Many Cardiovascular Workouts Are Healthy and How Many Are Harmful

The optimal dose of cardio is likely to differ from person to person and has not been precisely determined at this time. So far, current research indicates that 2.5-5 hours of moderate to vigorous physical activity per week will be most beneficial.

However,>10 hours/week may already reduce these health benefits.

Conversely, a sedentary lifestyle and excess weight, in addition to being the causes of premature death and disability, have many adverse consequences, especially for the cardiovascular system (CVS). About half of the US adult population today suffers from some form of CVD [1].

Exercise is one of the powerful tools for preventing cardiovascular diseases [2]. Together with an improvement in the state of CVD, the development and severity of coronary heart disease (CHD) are prevented. The risk of other diseases is reduced.

There is such an indicator – MET – “metabolic equivalent of task.” Each additional unit of MET reduces all-cause mortality by 30% in untrained people (who initially have <5 MET of exercise) [3].

And here’s another serious figure: physically active middle-aged people will, on average, live 8 years longer than “sedentary” ones, and for patients with diagnosed CVD, cardiac rehabilitation improves prognosis and quality of life [4].

Cardiovascular workouts positively affect almost every aspect of the body and brain, improving physical and mental well-being; staying physically active is one of the best ways to maintain health and extend your life expectancy.

While the ideal cardiovascular workouts dose has yet to be determined, it is clear that at least half of Americans are not gaining the recommended 150 minutes of moderate physical activity per week.

Even low- to moderate-intensity physical activity for as little as 15 minutes a day provides significant longevity benefits, which is about half the recommended minimum dose. The most dramatic risk reduction is observed by transitioning from a completely sedentary lifestyle to a slightly active one [7]. On the other hand, about 2.5% of American adults overdo exercise, thereby exposing themselves to potential detrimental health effects [7].

The topic of the optimal dose of cardiovascular workouts to ensure the best health and longest life is actively discussed in the scientific literature. The purpose of this article is to clarify this issue by focusing on the totality of accumulated data [8-14].

Cardio Effect Curve

The optimal dose of physical activity that brings maximum health benefits is still unknown to us [15]. As early as 2,500 years ago, Hippocrates taught: “If we could give each person the right amount of food and exercise – not too little and not too much – we would find the safest path to health” [7]. Even then, scientists understood that a certain range would be optimal for improving well-being and longevity; less or more training volume reduces the benefits.

Paffenbarger, back in 1986, described the relationship between physical activity (walking, climbing stairs, and playing sports) and all-cause mortality using a reflected J-curve. The study followed 16,936 Harvard graduates for 16 years and found the relationship that moderate exercise reduces risks the most [16].

Since then, numerous large observational studies involving more than 3 million people collectively have shown similar results, suggesting that there is likely to be an upper threshold at which very high doses of vigorous exercise are likely to be associated with losing some of the longevity benefits associated with less extreme doses of vigorous exercise.

As shown in the graph below, almost all large observations reproduce this reflected J-curve. It shows how the risks of CVD and premature mortality are reduced in a dose-dependent manner until an activity threshold is exceeded, after which the benefits are reduced. This risk reduction is not statistically significant in many studies due to the small number of individuals in the “extreme” cohort. However, this relationship is repeatedly revealed; in the largest studies, reducing health benefits seen with extremely high doses of exercise remains statistically significant [8].

Influence of Cardio Load on Various Diseases

Arrhythmia: x5 in veteran runners

Exercise has been associated with positive CVD adaptations, including enlargement of all heart chambers, improved function, increased compliance of the cardiac and vascular walls, sinus bradycardia, etc. [17, 18].

At the same time, there is a well-documented increase in the incidence of atrial fibrillation (AF) in endurance athletes. A survey of 300 veteran runners (mean age 47.5 years) revealed a 5-fold increase in the incidence of MA compared with a sedentary control group [19]. Since then, studies have found an association between MA and more intense training protocols, shorter finish times, and the absolute number of races completed [20].

Long-term enthusiasm for endurance training (≥2000 hours and/or ≥20 years of training) strongly correlates with MA even in individuals without CVD risk factors [21, 22].

Although the authors of individual studies have concluded that the likelihood of occurrence of MA can increase by 2-10 times, a recent meta-analysis quantified that the risk is increased by about 5 times [23].

As in many other cases, moderate doses of physical activity prevent MA, while too low and high volumes are associated with an increased risk of developing AF.

Inactive people (<6 METs) have an increased level of MA development (compared to more athletic people), and each additional 1 MET is associated with a 7% decrease in the risk of MA development [24].

In terms of the weekly dose of physical activity, even small amounts starting at 5 MET-hours / week appear to reduce the risk of AF, with the greatest benefit seen at 20 MET-hours / week (see graph below) [25] …

Above 55 MET-hours / week, which is approximately equal to 10 hours of intense physical activity per week, the likelihood of developing MA begins to exceed the risks of a sedentary cohort [25].

Myocardial Fibrosis

Myocardial fibrosis is a nonspecific response to various heart damage such as acute myocardial infarction, myocarditis, uncontrolled hypertension, and valve dysfunction. Pathological fibrosis of the heart predisposes to myocardial rigidity, arrhythmias, and other adverse consequences [31]. Myocardial fibrosis is best detected by cardiac magnetic resonance imaging (MRI), especially in the case of Paroxysmal nocturnal hemoglobinuria (PNH).

Chronic overload of endurance training increases the risk of PNH detection, and this has been found in healthy, asymptomatic endurance athletes [31-33]. In addition, PNH significantly and directly correlates with training experience (in years) and the number of completed marathons and other competitions with ultra-high endurance requirements [32, 34].

During intense training, cardiac output increases approximately 5 times compared to resting values ​​(from 5 L / min to 25 L / min or more), which leads to a disproportionately distributed load on the heart with an increase in wall load by 125% compared to from 4% to the right and left ventricles [35].

Combined with a sustained increase in catecholamines and reactive oxygen species, such stress is likely to cause cumulative myocardial injury, which ultimately leads to scarring, as indicated by PNH.

The presence of PNH can be detected by analyzing the number of ultramarathons in which the athlete took part or the severity of coronary artery calcification [34].

Cumulative MRI data of the heart show that PNH occurs in athletes in endurance sports in 12% of cases, which is 8 times higher than 1.5% in the control group with the minimum dose of physical activity recommended by the WHO (see graph below) [15].

Coronary Artery Calcification

A large body of data shows that the amount of calcium in the coronary arteries is an accurate predictor of CVD risk [37]. Paradoxically, although cardiovascular workouts reduce the risk of CHD, too much endurance training appears to significantly increase calcification, which brings us back to the J-curve plotted graph (Fig. 4) [38].

Athletes aged 54 ± 8 years have about 2 times more atherosclerotic plaques than the control group; also, these athletes have a higher degree of calcification [39].

Overall, studies have confirmed that aged endurance athletes have higher levels of coronary calcification than sedentary controls, but they generally have fewer dangerous plaques of mixed calcification and lipid origin [39–41]. Despite this, the highly active individuals show a slight tendency to reduce mortality compared to the less active cohort [40].

Acute Risks Associated With Intense Cardiovascular Workouts

Up to 90% of all exercise-related sudden cardiac deaths (SCDs) occur in amateurs rather than competitive athletes, with rates ranging from 1: 22,000 to 1: 69,000 in adults, compared with 1: 50,000 in youth athletes participating in competitions [43, 44]. The risk of SCD is highest during and immediately after cardiovascular workouts [15]. One study found that the risk of SCD increased 17-fold for a short time during and within 30 minutes after the end of an intense training session.

This risk is much higher in less active people than those who exercise more often (relative risk 74 versus 11) [15]. Another study also found that the sedentary cohort had a 25-fold higher risk of SCD than those who exercised at least a little [15].

In athletes over 35, more than 80% of SCD was caused by coronary artery disease (CHD); while among younger athletes (<35 years), the most common causes of SCD were congenital anomalies of the heart muscle, coronary vessels, and the vascular system [45].

Longer, more physically challenging runs appear to increase the risk of SCD. Data from nearly 11 million long-distance runners indicates a higher BCC prevalence in marathons (1.01 / 100,000) than half marathons (0.27 / 100,000). Only 29% of the victims were able to survive cardiac arrest [46].

It should be noted that the mortality rate for men was more than 2 times higher than that for women (0.98 versus 0.41 / 100,000) [47].

Triathletes are reported to have higher HRV than marathoners. When analyzing the data of 4.7 million triathletes, the frequency of SCD was 1.74 / 100,000 [48].

As in marathons, the risk for men is 3 times higher than for women (2.40 versus 0.74 / 100,000).

In addition, the risks are 3 times higher for men over 40 compared to younger participants [48].

Acute myocardial infarction (MI) is also more common during or shortly after intense cardiovascular workouts. Several studies have found that the risk of myocardial infarction increases 2-10 times within an hour after exercise [15].

Endurance cardiovascular workouts, including marathons and ultramarathons, affect a number of biomarkers of cardiovascular disease. A study involving 40 athletes (marathon, triathlon, mountain biking) found that the ejection fraction of the right ventricle after the race decreased by 9%. Regular exposure to strenuous exercise on the right ventricle can cause myocardial necrosis, which ultimately leads to scarring and irreversible remodeling, creating the prerequisites for arrhythmias. The approximate amount of physical activity leading to this effect is estimated to be> 20 hours per week for> 20 years [43].

Conclusions: Health Stress Should Be Moderate

• Regular, moderate-intensity cardiovascular workouts are important to reduce the risk of cardiovascular disease and increase life expectancy.
• Excessive amounts of intense training diminish the benefits of less extreme doses.
• The best forms of exercise to improve mental health and longevity are social sports such as tennis, golf, badminton, football, basketball, volleyball, and others, which improve physical fitness and strengthen interpersonal connections and tend to relieve stress [51].

The available data do not allow unambiguous recommendations for amateur athletes to reduce the amount of physical activity, especially if their activities improve the quality of life or allow them to compete successfully, since the risks remain quite uncertain.

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More about this topic: 

• Running for Beginners Guide + Tips
• Treadmill vs. Running Outside – Comparison
• Heart Risks Associated With Extreme Exercise – Health Essentials from Cleveland Clinic 

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