Sedentary lifestyles are rampant across the globe. In the U.S., approximately 55% of adults engage in sedentary behaviors (such as sitting around too much). While exercise is critical for maintaining a healthy body, the explosive growth in the number of exercise fads and fitness venues/options has led some of us to ask, “Can too much exercise be bad for your health?” The answer as to whether it's possible for an individual to exercise too much is, more often than not, that physical activity is highly beneficial. However, as is the case with many aspects of our lives, moderation is key. While many of us are aware of the consequences of too little exercise, less attention has been placed on what happens when one engages in too much exercise.

In this report, we describe recent research that examines the health impacts of exercise, the levels of exercise that may lead to health detriments, and potential risk factors that might predispose an individual toward exercise-induced impairments.

Not all exercise is created equal

Before diving into the impact of excess exercise, it is important to outline the differences between aerobic and anaerobic exercises, which affect the body in different ways. 

Aerobic exercises are rhythmic activities designed to be maintained for sustained periods of time. These include:

• Hiking
• Marathon running
• Cycling
• Swimming

Aerobic exercises utilize oxygen to provide energy to large muscle groups. These exercises rely on the capacity of the cardiorespiratory system (hearts, lungs) to supply oxygen and the ability of skeletal muscles to use that oxygen. Initially, standard endurance exercises aim for a zone 2 heart rate zone (60-70% of your maximum heart rate) for optimal energy utilization and weight loss.

Anaerobic exercises are short in duration and intense in nature and include activities such as:

• Powerlifting
• Sprinting‍
• High-intensity interval training (HIIT)‍
• Calisthenics (push-ups, pull-ups, etc.) 

Unlike aerobic exercises, anaerobic exercises do not require oxygen as a component for energy metabolism and fall within training zones 4-6 (80-100% of max heart rate). Instead, the mitochondria within our cells make ATP (Adenosine 5′-triphosphate, energy molecules found in cells) through biochemical processes (glycolysis, fermentation) to engage fast twitch muscles. 

Exercise “dose” is also a consideration

In addition to exercise “type” (aerobic, anaerobic), another way to understand how much physical activity we need to achieve health benefits (or detriments) is to think of exercise as “doses of medicine.” Several studies have revealed that “doses” of exercise, especially aerobic exercises, follow a “U-shaped” dose-response curve. However, more recent studies have challenged the U-shaped dose response curve for exercise and instead propose “reverse J-shaped” curves. More specifically, these studies have found that mortality risks with the highest doses of running are still significantly lower than for sedentary individuals. However, there are diminishing returns as physical activity increases, a point we’ll explore more later in the section, “What is too much exercise?”

How much exercise do we need?

For the average person, some exercise is clearly better than none. Most experts agree that even a little exercise is critical for maintaining health. The American Heart Association (AHA) recommends at least 150-300 minutes of moderate or 75-150 minutes of vigorous aerobic exercise per week. The implication here is that regarding fitness/movement/exercise, moderation is key. Other reports conclude that even at 10 times the recommended level, exercise confers benefit with no evidence of harm. 

The substantial health benefits associated with aerobic and anaerobic exercise include the following:

• Aerobic exercise significantly improves oxygen utilization in individuals that suffer from heart failure after a heart attack. Additionally, aerobic exercise can increase cardiac output by four times and can prevent cardiac aging.‍
• Aerobic and anaerobic exercises improve lipid profiles, particularly by increasing high-density lipoprotein cholesterol (“good cholesterol”). 
• Higher oxygen consumption (an outcome of increased physical activity) is associated with improved glucose regulation and reduced risk for type 2 diabetes (T2D). 
• Broadly speaking, exercise has positive effects on cognitive function and mental health. ‍
• Aerobic and anaerobic exercises can increase levels of β-endorphins (a natural pain reliever produced in the body).

Overall, scientists and health experts suggest a combination of both aerobic and anaerobic exercises for maximum health benefits. Since the AHA recommends around 150 minutes of moderate exercise a week, there are plenty of combinations you can try to keep your workout fresh and interesting. 

What is too much exercise?

Is it possible for an individual to exercise too much? The consensus among researchers regarding an “upper-limit” for exercise has been inconclusive. Problems with clinical study design and data variability have, frankly, hindered the scientific efforts to get to the bottom of this issue. For example, the ways in which the amount of exercise is reported ranges from self-report measures to a variety of controlled intervention methods. Whether these measures might apply to your exercise regimen and health status should be observed with caution, especially since much depends on your individual health profile and athletic status, as we’ll discuss later. 

Despite the inadequacies of the research to date, there are some rather convincing reports concluding that strenuous exercise may have certain negative impacts on health. Furthermore, certain pre-existing risk factors might exacerbate the potential determinants that come with extreme levels of physical activity. 

• In a large study of 17,589 men and women aged 20-98 years, researchers found that jogging two and a half hours a week at a frequency of three times a week was associated with the lowest mortality rate. However, both low rates (less than one hour per week) and high rates (more than four hours per week) of jogging were associated with higher mortality rates. 
• Other studies have demonstrated that while moderate doses of physical activity (e.g., walking, cycling, gardening, housework) for 2-3 times per week reduce risk of coronary heart disease (compared to a sedentary lifestyle), risk begins to increase when that exercise level is repeated daily. However, it is important to clarify here that the cardiovascular risk level of those who engage in daily physical activity, while higher than for those that exercise fewer times/week, is still lower (i.e., better) than the risk level of sedentary individuals. In other words, increasing doses of exercise beyond a certain amount may not confer additional benefits. ‍
• Excellent aerobic endurance capacity has been associated with improved responses toward psychosocial stress. On the other hand, there are also reports that heavy exercisers experience an increase in mental health issues and stress. 

Most studies reporting potential negative consequences of strenuous physical activity have made those observations in groups engaging aerobic exercises. However, there are also potential risks when high-intensity anaerobic exercises are practiced to excess:

• One study demonstrated that leg bench presses (up to 95% of maximum effort) can temporarily raise blood pressure to 400 mmHg in trained weight lifters. Given that animal studies have shown that just a 20-30 mmHg increase in perfusion pressure can dramatically reduce coronary artery function for several hours, this is potentially alarming. 
• Another report demonstrated that a single set of leg bench press reps in sedentary individuals significantly reduced brachial artery diameter, a measure of flow-mediated dilation that — when low — is predictive of cardiovascular disease.
• The mitochondria within our cells are critical for energy metabolism, and impairment in mitochondria function can lead to deteriments in glucose metabolism. Anaerobic exercises such as high-intensity interval training (HIIT) powerfully stimulate mitochondrial biogenesis to produce energy for our muscles in the form of ATP. One group of scientists demonstrated that excess HIIT disrupted mitochondrial function and led to impairments in glucose regulation.

Is too much exercise bad for you?

The answer to this question is highly dependent on the individual, their health profile, and the type of athlete they’ve been and are currently.

Top athletes 

These individuals regularly engage in strenuous activity, and generally speaking they face the following risks/consequences from too much exercise: 

• Aerobic exercise increases cardiac output by eightfold in elite athletes. Although this dramatically improves performance, it also places these athletes at greater risk of cardiac disease. In general, it appears that elite endurance athletes are at greater risk of developing cardiovascular impairments. 
• Studies have shown that athletes exhibit myocardial fibrosis, and researchers suggest that temporary injury during exercise may induce scarring.  
• Other reports have shown that some endurance athletes, particularly the most elite, eventually have long term impairments and remodeling of the right ventricle. ‍
• Elite endurance athletes are at risk of atrial fibrillation when physical activity goes to the extreme. 

Individuals with pre-existing medical conditions

These individuals may be predisposed to detriments that come with strenuous exercise:

• High-intensity exercise increases atrial fibrillation risk in men older than 65 years.
• While running and walking reduce cardiovascular mortality after a cardiac event, these benefits are reduced with excess exercise. 
• Strenuous exercise may augment the risks for cardiac diseases among those who are genetically predisposed to such disorders. For example, hypertrophic cardiomyopathy, a common genetic heart disease, can contribute towards myocardial fibrosis induced by excess physical activity — a common cause of sudden death in competitive athletes. ‍
• One study examined patients with the Lamin A/C genotype (Lamin A/C cardiomyopathy is an inheritable form of heart disease) and found that active Lamin A/C patients had worse systolic function compared to inactive patients. Interestingly, the active Lamin A/C patients in this study were not engaging in an excess of exercise; thus, clearly these individuals are at a relatively low safety threshold for physical activity. 

Key takeaways 

Is it possible for an individual to exercise too much? Although clinical research has uncovered several links between extreme levels of physical activity and certain health detriments, the studies examining these associations are continually evolving and require further investigation. Obesity and sedentary lifestyles, rampant in Western societies, represent a far greater health risk than does excessive exercise. The safest bet: follow the AHA recommended guidelines for physical activity, moderating that recommendation as your individual health profile necessitates (ask your medical providers for guidance), take breaks, and have fun!