The physical activity is one of the best “preventive drugs” for many common ailments, from psychiatric disorders to heart disease, diabetes, and cancer.

However, as with other medications, there’s the matter of dosage. Too little exercise and you won’t get much benefit. 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.

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 studies 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, 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.

How and Why Extreme Cardio May Damage Your Heart

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.

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.

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.