Why Too Much Exercise May Harm Your Heart, and What Science Tells Us About the Ideal Amount and Type of Exercise
Few people would ever consider pushing the limits of their endurance like Ben Lecomte, the first person to swim across the Atlantic Ocean. Now he’s planning to swim across the Pacific Ocean, from Tokyo to San Francisco — a wet and lonely 5,500-mile journey that will take about five or six months to complete.
As reported by NPR:1
“Lecomte, who lives in Austin, Texas, is diving back into the ocean to focus attention on environmental problems …. During the swim, he will collect data on the Pacific, including the microbes and trash he encounters.
People can follow along on his Facebook page,2 ‘The Longest Swim.'”
This is the epitome of extreme exercise, and cardiologist Dr. Benjamin Levine, director of the Institute of Exercise and Environmental Medicine will study Lecomte’s heart and health during this event.
To do that, he’ll be using the same technology NASA uses to monitor the health of astronauts on the International Space Station.
Chances are Lecomte will damage his heart to some degree, because contrary to popular belief, more does not necessarily equate to better health when it comes to exercise. There’s a “Goldilocks zone,” beyond which the damage incurred outweighs the benefits.
Exercise Is Good Medicine at the Right Dosage
Modern fitness research offers many potent reminders that physical activity is one of the best “preventive drugs” for many common ailments, from psychiatric disorders to heart disease, diabetes, and cancer.3
For example, one meta-review4 of 305 randomized controlled trials comparing the effectiveness of exercise versus drug interventions on mortality outcomes found “no statistically detectable differences” between exercise and medications for prediabetes and heart disease.
One of the key health benefits of exercise is that it helps normalize your glucose, insulin, and leptin levels by optimizing insulin and leptin receptor sensitivity. This is an important factor for optimizing your overall health and preventing chronic disease.
Another way in which exercise promotes good health and longevity is by forcing your mitochondria (those little “power stations” inside your cells that produce energy or ATP) to work harder, thereby producing more mitochondria (biogenesis) to keep up with the heightened energy requirement.
A side effect of this is a slowing down of your biological aging process.
However, as with other medications, there’s the matter of dosage. Too little exercise and you won’t get much benefit. (Worse yet, chronic inactivity has been shown to be an independent risk factor of chronic disease and early death.)
On the other hand, exercise too much, and you could do harm. As noted by Dr. Levine, while endurance athletes live longer than non-athletes — in general, nearly 20 percent longer than non-runners — the evidence also shows that going overboard does put your health at risk.
One of the risks of excessive high intensity cardio is you can develop enlargement of your heart that leads to something called diastolic dysfunction which can lead to heart failure and is really an epidemic in the U.S.
What’s the Ideal Dose of Exercise for Optimal Health and Longevity?
Research has shown that once you reach 40 to 50 minutes of daily vigorous exercise, or just over an hour of moderate exercise (such as walking), the benefits from your efforts plateau, and further efforts do not convey additional improvements in life expectancy.
One of the largest, longest, and most recent studies5 to shed light on this “Goldilocks zone” found that those who walked or engaged in other moderate-intensity exercise for 450 minutes per week (right around one hour per day, seven days a week) lowered their risk of premature death by 39 percent compared to non-exercisers.
Those who exercised around 3.5 hours a day only reduced their mortality risk by 31 percent — the same risk reduction as those who met the guidelines of 150 minutes per week (about 20 minutes per day).
A second large-scale study,6 which focused specifically on intensity, found that spending 30 percent of your exercise time on strenuous, high-intensity activity can gain you an extra 13 percent reduction in early mortality, compared to never picking up the pace and breaking a sweat.
When it comes to endurance cardio, previous research (discussed in the TED Talk below) has shown that to optimize the health benefits from running you’ll want to run 5 to 20 miles per week — the ideal amount being 10 to 15 miles per week. Once you reach 25 miles or more per week, the benefits again disappear.
Also, if you run too fast — over 8 miles an hour — the benefits tend to go away (note we’re talking about speed in long distance endurance running here, not interval sprinting). Lastly, if you run seven days a week, the benefits also disappear. The ideal amount was found to be a 30-minute run, two to five days a week.
So, the key really is moderation — moderation in terms of intensity, duration, and frequency. The human body simply wasn’t designed to engage in long-term extreme athletic performance, like battling ocean waves for 8 hours a day for six months straight.
Exercise Less — Move More
Some people may be a bit confused by my exercise recommendations because on the one hand, I advocate high-intensity exercise, and on the other, I’ve repeatedly pointed out that non-exercise movement may be even more important than a regular exercise routine.
It’s really not a contradiction, if you stop and think about it. The fact of the matter is that working out really hard for an hour and then spending the majority of the rest of your day sitting down is not going to do you much good, because the latter counteracts the former.
Research has demonstrated that six hours of uninterrupted sitting counteracts the positive health benefits of one hour of exercise. So the foundation for good health is relatively constant or regular movement, i.e. avoiding sitting down as much as possible, because even just standing up produces beneficial biological effects.
I firmly believe that walking say 7,000 to 10,000 steps a day is key for health and longevity. Now that I’m a full-time resident of Florida, I walk barefoot on the beach for about one hour each day. I used to do two hours but realized that the extra time was not providing any additional health benefits based on the information reviewed in this article. Balance and moderation is the key.
This lays the groundwork or foundation, so to speak, on top of which you can then build your fitness to increasingly higher levels. For maximum benefits with a minimal time investment, high-intensity interval training (HIIT) is an ideal add-on, two or three times a week — and no more than that, as your body needs to recuperate in between sessions.
Walking + HIIT = A Natural and Comfortable Combination
Benefits of HIIT include cardiovascular fitness, improved muscle growth and strength, and the generation of “anti-aging” human growth hormone (HGH), also referred to as “the fitness hormone.” It also effectively stimulates your muscles to release anti-inflammatory myokines, which increase your insulin sensitivity and glucose use inside your muscles.
They also increase liberation of fat from adipose cells, and the burning of the fat within the skeletal muscle. This is why HIIT tends to be very effective for weight loss. If you’ve already incorporated more walking into your day, a natural progression would be to simply switch up the pace at regular intervals, interspersing bouts of speed walking followed by more casual strolling.
In study after study we find that it is this intermittent high and low intensity that appears to produce the most significant results, and there’s nothing that says you have to do HIIT on an exercise machine. You can just as easily incorporate it into your daily walking routine. By exerting yourself intermittently when walking, you can dramatically increase the return of your effort without spending any extra time on it.
How and Why Extreme Cardio May Damage Your Heart
HIIT has another benefit, and that is improved safety. While you can certainly overdo it on HIIT — the Tabatha protocol for example should only be attempted by extremely fit people — endurance cardio tends to be a lot riskier, in large part because your body does not have enough time to recover and repair the damage.
Extended extreme cardio sets in motion inflammatory mechanisms that damage and prematurely age your heart. Your heart pumps about 5 quarts of blood per minute when you’re sitting. When you’re running, it goes up to 25 to 30 quarts, and it wasn’t designed to pump this amount of blood for hours on end, day after day.
When pushed in this way, your heart basically enters a state of “volume overload” that stretches the walls of your heart muscle, literally breaking fibers apart.
Failure to fully recover between runs compounds the problem. Many endurance athletes live in a perpetual post-workout state, which resembles chronic oxidative stress. This repetitive and unrelenting damage to the heart muscle increases inflammation that leads to increased plaque formation, because plaque is your body’s way of “bandaging” the lining of your inflamed arteries.
Over time, as more damage is inflicted, the heart enlarges (hypertrophy), and forms scars (cardiac fibrosis). MRIs of long-time marathoners reveal abundant scarring all over their hearts. Scientists have also measured elevated cardiac enzyme levels after extreme exercise — just like after a heart attack, which can only mean one thing: this type of exercise is damaging to your heart.
In essence, while you may appear super fit by any number of measures, you run the risk of dropping dead from cardiac arrest, which is exactly what has happened to more than one marathoner over the years.
‘Moderately Fit’ Wins the Race
The myth that extreme endurance cardio is good for your heart took root when, in 1977, Dr. Thomas Bassler boldly proclaimed that “completing a marathon confers immunity against heart attack.” Many die-hard runners (and many doctors) still believe this to be true. But a growing number of studies7,8 on endurance athletes have demonstrated the hazards of extreme cardio, including the following:
- Marathon runners and triathletes tend to incur scarring in the center of their heart (the septum)
- Lifelong endurance athletes tend to have more coronary artery calcification9 than you’d expect to see in people with lower risk factors
- Veteran endurance athletes have a 5-fold increased risk of atrial fibrillation, a dangerous irregular heart rhythm that can progress into full cardiac arrest
- Some endurance athletes also present ventricular tachycardia (a heart rhythm faster than 100 to 120 beats per minute), which can lead to ventricular fibrillation — a leading cause of sudden cardiac death
- Excessive endurance exercise during your younger years may increase your risk of developing heart problems later in life. A Swedish study10 found that men who, at the age of 30, had exercised intensely for more than five hours a week compared to less than one hour a week, were 19 percent more likely to have developed an irregular heartbeat (a key factor in stroke risk) by the time they hit their mid-40s.
Meanwhile, daily walking or bicycling for an hour per day in older age was inversely associated with atrial fibrillation
Several more studies detailing the adverse health effects of extreme endurance cardio can be found in my previous article, “Extreme Endurance Exercise Could Be Damaging Your Heart.” As noted by Dr. James O’Keefe, a research cardiologist and a former elite athlete, in the TED Talk above:
“Darwin was wrong about one thing. It’s not survival of the fittest, but survival of the moderately fit … ‘We weren’t born to run. We were born to walk, and we need to be walking more … you need to be moving your body more than sitting — every chance you get, move!'”
HIIT May Be Ideal for Cardiac Patients
Whereas endurance cardio can damage your heart, HIIT has been shown to safely promote heart health, which makes sense when you consider that this form of exercise effectively mimics our ancestral ways of life. By exercising in short bursts followed by periods of recovery, you recreate exactly what your body needs for optimum health, and that includes the production of growth hormones, the burning of excess body fat, and improved cardiovascular health and stamina.
In a Canadian study,11 middle-aged men and women diagnosed with cardiovascular disease were asked to participate in a program of cycling intervals as their exclusive form of exercise. After several weeks on the program, they showed significant improvements in their health and fitness.
Most remarkably, they showed “significant improvements” in both heart and blood vessel functioning. And, contrary to what popular belief might dictate, the intense exercises did not provoke any heart problems.
It’s believed that the short duration helps insulate your heart from the intensity. That said, while most people of average fitness will be able to do HIIT safely, if you have a history of heart disease or any medical concern, please get clearance from your health care professional before you embark on a HIIT program.
7 Signs You May Be Overdoing It
While HIIT is inherently safer than endurance cardio, it’s very important to carefully consider the frequency of your sessions to give your body enough time to recover. If you don’t, HIIT also has the potential to do more harm than good. To maximize your workout efforts, you’ll want to push hard enough to challenge your body at your current level of fitness, while allowing your body to fully recuperate in between sessions.
If you’re doing high intensity interval exercises, it’s NOT recommended to do them more than three times a week. If you’re unsure whether you may be pushing yourself too hard, the following seven symptoms may signal that you need to cut back a bit and allow your body to recover:
- Exercise leaves you exhausted instead of energized
- You get sick easily (or it takes forever to get over a cold)
- You have the blues
- You’re unable to sleep or you can’t seem to get enough sleep
- You have ”heavy” legs
- You have a short fuse
- You’re regularly sore for days at a time
Listen to Your Body, and Move More
When it comes to exercise, especially the more vigorous kind, be sure to listen to your body and don’t ignore signals of distress. It’s time to put away the outdated “no pain no gain” principle. You can fully optimize your health and fitness without killing yourself in the process — either figuratively or literally. To summarize the key points covered in this article:
- Stand up and move about as much as possible throughout the day. A stand-up desk is a worthwhile investment that can pay dividends in terms of health and longevity
- Aim to walk about 10,000 steps (or about one hour) seven days a week, at a moderate pace. Intermittently picking up the pace will further boost your health benefits by imitating HIIT. Other moderate-intensity exercises such as swimming, bicycling, etc also count of course. Your goal is to get 450 minutes of moderate-intensity movement per week
- Aim for a well-rounded fitness regimen that includes HIIT. Research has clearly demonstrated that short bursts of intense activity is safer and more effective than conventional cardio — for your heart, general health, weight loss, and overall fitness. Just make sure you allow your body to sufficiently recover between sessions.
An equation to keep in mind is that as intensity increases, frequency can be diminished. For more details on my latest fitness and workout recommendations, see my “2015 Exercise Recommendations and Update.”
If you enjoy running, an ideal amount is 10 to 15 miles per week, divided up into 30-minute runs, two to five days a week.