The reason some athletes have a fast resting heart rate has nothing to do with their training. Athletes can have medical conditions that cause a fast resting pulse.

Conditions that Cause a Fast Resting Heart Rate (in athletes and non-athletes, no particular order)

• Heart arrhythmia (SA node-re-entry)

• Sleep apnea (myth: You can’t have sleep apnea if you’re lean and athletic)

• Inappropriate sinus tachycardia

• Hyperthyroidism (overactive thyroid)

• Pheochromocytoma (excess adrenaline production)

• Problem with the autonomic nervous system

• Reactive hypoglycemia.

• Anxiety disorder

Sinoatrial node re-entry. Sometimes this rare condition is misdiagnosed as an anxiety disorder. Dizziness or lightheadedness are additional possible symptoms.

Symptoms may last minutes to a few hours and begin and end abruptly. Thus, this cause of fast heart rate is not always present.

When there’s no episode of this sped-up pulse, the athlete who has SA node re-entry actually has a normal heart rate and rhythm.

Sleep apnea.  You can be the fittest person in the world and still have sleep apnea.

Though obesity is a driving force behind many sleep apnea patients, the cause can also be from inefficient pharyngeal anatomy — something that you were born with, namely, a naturally small airway.

“Patients with obstructive sleep apnea also have faster heart rates during resting wakefulness,” says a paper in the Journal of the American College of Cardiology (August 2008).

Inappropriate sinus tachycardia. Similar to SA node re-entry, except that the acceleration of the heart rate begins and ends gradually.

In the absence of an episode, however, the athlete with this condition may have a somewhat elevated pulse.

Neither of these conditions are caused by overtraining.

Overactive thyroid. Athletes aren’t immune to this. Resting pulse may be over 100 bpm.

Other symptoms include sudden unexplained weight loss, heat sensitivity, sweating, muscle weakness, brittle hair and trembling hands and fingers.

Pheochromocytoma. This is a rare benign tumor of the adrenal gland. In addition to a rapid heartbeat, symptoms include severe headache, shortness of breath and severe sweating.

Autonomic nervous system dysfunction. The ANS controls, among other things, heart rate. There are many causes of an ANS dysfunction.

Reactive hypoglycemia. In layman’s terms, this means a dive in blood sugar level in response to eating.

The rapid heart rate occurs soon after the meal, and the meal usually includes a lot of simple carbohydrates, such as a stack of pancakes with syrup.

Anxiety. If an athlete has a fast resting heart rate but has not been overtraining, and does not have other symptoms, chances are likely that the athlete is suffering from a free-floating or some other anxiety disorder.

Some things cause a transient fast resting pulse such as smoking and premenopausal/menopausal hot flashes, but when the heart rate is almost always elevated (over 100 bpm) whenever it’s being taken, this should be brought to the attention of a doctor.

And here’s something interesting to consider: It’s just possible that the athlete gets nervous whenever a pulse is taken, and this situational anxiety accelerates the pulse to over 100 bpm!

If this is the suspected cause, it would be great to get an app that periodically—without the user knowing it—records resting heart rate.

Sources:
verywell.com/sinus-nodal-reentrant-tachycardia-snrt-1746254
mayoclinic.org/diseases-conditions/hyperthyroidism/basics/symptoms/con-20020986
mayoclinic.org/diseases-conditions/pheochromocytoma/basics/definition/con-20030435
medlineplus.gov/autonomicnervoussystemdisorders.html; emedicine.medscape.com/article/122122-clinical; sciencedirect.com/science/article/pii/S0735109708016483 fast resting pulse athletes