What Martha the Rhino Can Teach You About Running and Your Risk of Heart Disease

A woman, we’ll call her Martha, ran the entire race dressed in a rhino costume. The suit weighed 16 kilograms (35 pounds), which placed an extra strain on her heart.

Some researchers decided it would be interesting to see how running in the suit would affect Martha’s heart rate.(1) After all, it’s not every day that a rhino runs a marathon.

Martha kept an average heart rate of 181 beats per minute for 4 hours and 35 minutes — 14% higher than her average heart rate for a half marathon *without* a rhino suit, and 350% more than her resting heart rate.

The researchers called this feat “remarkable.” Even more impressive was that rather than feeling tired or in danger, “she commented that at no time during the run did she feel overly stressed and… finished in good spirits.”

This kind of performance is not uncommon for endurance athletes. Most marathoners also don’t report chest pain or other symptoms of a heart attack after a race.

However, this doesn’t mean their hearts aren’t damaged. When people say that their whole body is tired after running a marathon, doing a triathlon, or biking 100 miles, this includes their heart.

In this article, we’ll examine the first step of the Cardiotoxicity Cycle.” We’ll look at how cardio reduces your heart function after a workout, and whether or not this is a bad thing.

How Cardio Makes Your Heart Suffer

There’s no doubt that endurance exercise can place stress on your heart:

• It’s common for runners, cyclists, swimmers, and other endurance athletes to maintain a heart rate of well over 130 beats per minute for hours on end.(2-5)
• During a race like the Tour de France, a professional road cyclist can average 145 beats per minute (bpm) for around 90 hours.(6,7)
• Your heart can consume six times more oxygen during heavy exercise than at rest and pumps eight times more blood.(8,9)
• Oxidative stress and inflammation can increase exponentially.(10-14)
• Stress hormones go through the roof.(15)
• Blood pressure and stress on your heart and blood vessels skyrocket.(16,17)

Almost all evidence suggests that small amounts of “exercise” stress are beneficial,(18-25) but there’s still concern that too much can damage your heart. The first wave of unsettling evidence starts to appear towards the end of a long workout.

If you look at this graph, you can see that Martha the Rhino’s heart rate increased throughout the race. This is known as “cardiac drift,” and it’s part of a phenomenon called “cardiac fatigue.” Some researchers think this is one of the first steps in the process by which cardio damages your heart.

How Cardio Decreases Your Heart Function after a Workout

Your heart is zonked after a hard cardio workout because of cardiac fatigue.(26-55)

• Your heart becomes stiffer, fills with blood slower, and doesn’t allow as much blood inside.
• Your heart ejects less blood per beat and compensates by increasing your heart rate (cardiac drift).(56,57)
• Small patches of your heart can contract when they’re not supposed to or with the wrong amount of force.
• Your blood pressure drops because your heart isn’t able to pump as hard.
• The heart becomes less sensitive to catecholamines and less responsive to the nervous system.

Your heart is exhausted and becomes dysfunctional after a long hard endurance workout. These changes also often occur after severe heart damage like heart failure or a heart attack.(58-66)

Some researchers believe that cardiac fatigue caused by cardio may also be a sign of heart damage.(67,68) They’re probably wrong.

6 Reasons Why Decreased Heart Function is Probably Not Dangerous for Athletes

The good news is that it’s not clear if this short-term drop in heart function is bad, and most evidence indicates that it’s not.

1. In almost all cases, healthy athletes with cardiac fatigue don’t have many of the classic symptoms of heart damage, like chest pain, nausea, dizziness, or dyspnea (the inability to catch your breath). This doesn’t prove heart damage hasn’t occurred, but it means it’s less likely.(69-71)

2. In most cases, heart function is completely back to normal within hours or one to two days.(72-81) It can take a little longer to get back to 100% after really hard workouts, but it’s still on an upward trend. This indicates the changes are not permanent.(82,83)

3. Well trained athletes usually experience less cardiac fatigue. This suggests that it’s part of an adaptation to training rather than a sign of heart damage.(84)

4. Cardiac fatigue doesn’t seem to reduce exercise performance, which usually does occur with real heart damage.(85)

5. There is no evidence of new permanent heart damage after endurance exercise when athletes have cardiac fatigue (except for blood tests that we’ll cover in another article).(86-90)

6. Endurance training improves heart function over the long-term. Also, endurance athletes tend to have the same or better heart function compared to healthy non-athletes and other athletes.(91-126)

It’s not exactly clear why heart function drops after cardio, although most research indicates it’s similar to how muscles fatigue after strength training.

The heart:

• Is pushed past its comfort zone.
• Temporarily weakened.
• Recovers.
• Returns to an even higher level of performance.

This pattern suggests that the drop in heart function after cardio is part of a long-term process that makes your heart stronger. Heart function drops after a workout, recovers, and tends to increase to an even higher level over time.

Are “Heart Hiccups” an Exception?

Some aspects of heart function don’t necessarily improve over the long-term, but they don’t get worse either. For example, one study found that some athletes’ heart valves don’t close properly after an Ironman triathlon.(127)

These valve closing problems are called “valvular regurgitations.” We’ll call them “heart hiccups” for simplicity.

A few studies have found that endurance athletes have a higher rate of “heart hiccups” than non-athletes.(128,129) However, there’s little evidence to suggest that these mildly leaky valves cause problems for otherwise healthy athletes. Most studies indicate they’re benign.(130-134)

Some studies have shown that both endurance and strength athletes have more valve problems than non-athletes, while other studies have not.(135,136)

Valve regurgitations are common during pregnancy when the heart is also placed under stress, yet no damage occurs.(137) They’re also common in normal healthy people.(138)

Endurance athletes also tend to have excellent valvular function.(139-141)

This suggests that “heart hiccups” are another sign of a temporary drop in heart function that is followed by a long-term improvement.

Why a Twitching Heart is Probably not a Problem

Several studies have found “wall motion abnormalities,”or “heart twitches,” after ironmans and marathons — small patches of heart tissue that contract at odd times or with the wrong amount of force.(142-143) These motions also sometimes occur when people with heart disease exercise.(144,145)

It’s possible that these “twitches” of heart tissue are signs of heart damage, but they probably aren’t. A recent study using far more advanced imaging techniques found that athletes can develop these spasms of heart tissue without any sign of actual heart damage.(146)

The authors of the study concluded that the “twitches” were probably just another sign of the heart having trouble relaxing, not heart damage. These twitches also disappear after a week, which indicates they aren’t a sign of heart disease.(147)

Endurance training also changes the way the heart contracts over time. This may change how it “twitches” during and after exercise.(148-150)

Heart “hiccups” and “twitches” are probably just another sign of cardiac fatigue. There’s little reason to think they cause problems in the long-term.

Cardio Makes Your Heart Stronger over Time

 

Almost every aspect of heart function that drops after cardio is mirrored by an improvement over the long-term.

* Definitions

• Stroke volume is how much blood is ejected per heart beat.
• Heart strain and strain rate are measures of how well your heart allows blood inside. A higher strain rate is better.
• The E/A ratio is a measure of how efficiently blood is able to move through certain parts of your heart.
• Resting heart rate is the number of times your heart beats per minute when you aren’t moving.
• Systolic blood pressure is the peak force inside your arteries when your heart is contracting. 
• Diastolic blood pressure is the minimum amount of force inside your arteries when your heart is relaxing.
• (If a doctor says your blood pressure is “120 over 80,” the first number is your systolic blood pressure, and the second number is your diastolic blood pressure.)
• Catecholamines are hormones that tell your heart to work harder. A healthy heart is sensitive to catecholamines. Healthy people are able to produce as many catecholamines as they need.
• Heart rate variability is a measure of how well your nervous system is controlling your heart rate. A high heart rate variability is good.
• Valve regurgitations are when the valves of the heart don’t close completely (“heart hiccups”).
• Wall motion abnormalities are when small patches of heart tissue contract at odd times or with the wrong amount of force (“twitches”).

Notice that blood pressure tends to go down in the short-term and long-term. This doesn’t seem to fit the trend. However, blood pressure is higher during cardio and tends to drop over time, which is considered a good thing. 

It looks like Martha the rhino can relax — she probably didn’t destroy her heart.

Don’t Get too Excited — You Aren’t Safe Yet

The temporary drop in heart function after hard cardio workouts probably isn’t evidence that cardio damages your heart. That said, it also isn’t evidence that it doesn’t damage your heart.

It’s possible that in some rare cases cardiac fatigue may be a sign of heart damage. It’s also possible that cardiac fatigue is harmless and happens to occur at the same time as real heart damage (if cardio does damage your heart).

Heart function is usually measured using sound waves — a method called echocardiography. “Echo” as it’s called, is only part of the puzzle.

Cardiac fatigue is an indirect measurement of heart damage. Researchers are more worried about blood tests that seem to provide direct evidence that endurance exercise damages your heart. 

In the next article, we’ll determine if these blood tests prove cardio damages your heart or not.

Cardiac Fatigue is Not a Major Concern

Your heart function drops after a long hard cardio workout.

This can sometimes persist for several days or weeks (on rare occasions), but there’s little evidence it’s a sign of permanent damage. Your heart appears to recover and grow stronger over time.

You’re reading Part 2 of a series on whether or not exercise damages your heart. Click here to read Part 3.

You can read the first post in this series by clicking here.

A special thanks to Drs. Andre La Gerche, Ellen Dawson, Keith George, Rob Shave, Greg Whyte, Guenther Neumayr, Jürgen Scharhag, Aaron Baggish, and Jessica Scott for their assistance in making this article possible.

 

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