The United States has a big problem.
Heart disease is the number one cause of death, with one person dying every 39 seconds in the United States in 2008.(1)
To help counter this problem, you’ve been told for years that one of the best ways to protect your heart is to exercise — especially “cardio” like swimming, cycling, and running.
There’s plenty of data to support that advice,(2-4) but there’s also emerging evidence that too much cardio might damage your heart.
If this is true, it would mean that:
- Many of our best efforts to become healthier are really backfiring.
- Many of our favorite activities have been increasing our risk of an early death.
- As we watched athletes like Michael Phelps win 21 gold medals, we were also watching him damage his heart.
Most of the information on this topic has been in the form of overhyped news articles focusing on single studies, misinterpretations of the research, pet theories, and anecdotes. You deserve a clear answer — an unbiased, thorough, critical examination of a simple question:
Does cardio damage your heart?
Whether you do cardio for the health benefits, enjoyment, or both, wouldn’t you like to know if your exercise regimen is secretly killing you?
How Cardio Might Damage Your Heart
In theory, excessive cardio causes small amounts of damage in the short-term. These small injuries turn into more significant long-term changes that can hurt your heart, blood vessels, and even kill you. This is thought to occur in a four step process:(5-8)
- Endurance exercise places a higher than normal load on your heart. It increases your oxygen and energy needs. It raises stress hormones, heart rate, blood pressure, and strains the walls of your heart. It also causes oxidative stress and inflammation. The heart is starved for oxygen and overwhelmed with these demands, and in some cases is irreversibly scarred by the exertion.
- After each workout, your heart is tired from the effort and heart function drops. There are often changes in electrical activity, heart rate, and an increase in blood markers of heart damage. The inflammation and oxidative stress from the effort damages your heart, blood lipids, and blood vessels.
- With enough training, your heart increases in size, develops erratic electrical activity, loses some of its ability to function, and develops small patches of scar tissue that grow with more training. The blood vessels around the heart and throughout other parts of the body also become harder and develop thicker deposits of calcium and plaque.
- Over time, these long-term changes increase the risk of developing atherosclerosis, heart attack, coronary and peripheral artery disease, and in some cases, sudden cardiac arrest and early death.
We’ll refer to this process as the “cardiotoxicity cycle.”
The Cardiotoxicity Cycle
Here is a good TEDx video from Dr. James O’Keefe. He is the author of several recent studies claiming that chronic endurance exercise is bad for the heart. It provides a nice summary of the cardiotoxicity cycle.
We’ll be examining the claims in this video throughout this series.
The terms “cardio,” endurance exercise, and aerobic exercise mean the same thing, and we’ll use them interchangeably. The latter two descriptions are more accurate, but “cardio” is how most people refer to this kind of exercise.
Whatever you call them, these terms refer to any activity that keeps your heart working at a moderate to high level for 30 minutes or more.(9)
The researchers that suggest endurance exercise damages the heart recommend avoiding anything over an hour, and “…not more than seven hours weekly” of hard endurance training.(10)
Doing less than that is not considered to be harmful.
How Much is Too Much?
Every kind of exercise can probably damage your heart if you overdo it.
If you try to run 23 hours a day, every day, and something else doesn’t break first, you might get heart disease.
The question is whether the kind of training and racing that many passionate health enthusiasts and pros do can damage the heart.
We’re also going to assume that you’re practicing cardio in a progressive manner with adequate recovery between workouts. If you’re training 40 hours a week, with no rest days, on four hours of sleep per night, while maintaining a stressful day job, you shouldn’t be surprised if you get heart disease.
The point at which cardio (or any kind of exercise) starts to hurt more than help is different for everyone. One of the things you’ll learn in this series is where your personal exercise threshold may be.
A Critical Look at Cardio and Heart Disease
This series will examine each step of the cardiotoxicity cycle to see whether or not cardio contributes to heart disease, and if it does, what to do about it.
- What cardio does to your heart during a workout.
- How your heart function drops after an endurance workout, and whether or not this is bad for you.
- Why the blood tests that most studies use to measure heart damage are misleading for athletes.
- Whether or not you should worry about the inflammation and oxidative stress from endurance exercise damaging your heart.
- How cardio changes your heart, blood vessels, and biochemistry — for better or worse.
- How cardio increases or decreases your risk of having a heart attack, developing heart disease, and dying.
- What you can do to get all of the benefits of cardio without risking heart damage.
At the end of this series, you’ll be able to go for a bike ride, run, or swim without guessing if your favorite activity is shortening your life. You’ll be able to decide if the risks of cardio outweigh the benefits.
Now that we’ve identified the defendant and the charges, it’s time to see what the evidence has to say.
In the next article, we’ll start at square one — what happens to your heart during and immediately after a hard endurance workout.
Based on what you know now, do you think cardio contributes to heart disease? Leave your thoughts in the comments section below.
Disclosures: I have been competing in triathlons and other endurance events since I was four years old. I am willing to accept that cardio contributes to heart disease if the evidence supports that conclusion, but I also admit a certain level of bias in that I hope it does not.
This article was written with input from Imprüvism Advisors John Kiely and Dr. Sean O’Mara.
1 Roger VL, Go AS, Lloyd-Jones DM, et al. Heart disease and stroke statistics–2012 update: a report from the American Heart Association. Circulation. 2012 Jan 3;125(1):e2-e220. Epub 2011 Dec 15. Abstract: http://pmid.us/22179539 | Full Text: http://goo.gl/2PEod
2 Wen CP, Wai JP, Tsai MK, et al. Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study. Lancet. 2011 Oct 1;378(9798):1244-53. Epub 2011 Aug 16. Abstract: http://pmid.us/21846575 | Full Text: http://goo.gl/Xa1hX | Author Contact: <firstname.lastname@example.org>
3 Samitz G, Egger M, Zwahlen M. Domains of physical activity and all-cause mortality: systematic review and dose-response meta-analysis of cohort studies. Int J Epidemiol. 2011 Oct;40(5):1382-400. Epub 2011 Sep 5. Abstract: http://pmid.us/22039197 | Full Text: http://goo.gl/PH40x
4 Haskell WL, Lee IM, Pate RR, et al. Physical activity and public health: updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc. 2007 Aug;39(8):1423-34. Abstract: http://pmid.us/17762377 | Full Text: http://goo.gl/FtbFM | Author Contact: <email@example.com>
5 Patil HR, O’keefe JH, Lavie CJ, et al. Cardiovascular damage resulting from chronic excessive endurance exercise. Mo Med. 2012 Jul-Aug;109(4):312-21. Abstract: http://pmid.us/22953596 | Full Text: http://goo.gl/pxtJj | Author Contact: <firstname.lastname@example.org>
6 O’keefe JH, Patil HR, Lavie CJ, et al. Potential adverse cardiovascular effects from excessive endurance exercise. Mayo Clin Proc. 2012;87(6):587-95. Abstract: http://pmid.us/22677079 | Full Text: http://goo.gl/Q5MmQ
8 O’Keefe JH, Lavie CJ. Run for your life … at a comfortable speed and not too far. Heart. 2012 Nov 29. [Epub ahead of print]. Abstract: http://pmid.us/23197444 | Full Text: Received from author.
9 Coyle EF. Physiological determinants of endurance exercise performance. J Sci Med Sport. 1999 Oct;2(3):181-9. Abstract: http://pmid.us/10668757 | Full Text: NA
10 Patil HR, O’keefe JH, Lavie CJ, et al. Cardiovascular damage resulting from chronic excessive endurance exercise. Mo Med. 2012 Jul-Aug;109(4):312-21. Abstract: http://pmid.us/22953596 | Full Text: http://goo.gl/pxtJj | Author Contact: <email@example.com>