Health Myths of the Female Athlete | Myth 4
By Elissa Rosen, MD, CEDS
The following is the final installment of a four-part series on the Health Myths of the Female Athlete
Myth 4: Bradycardia, or slow heart rate, is always a sign of good fitness in a female athlete.
Truth: The medical definition of bradycardia is a heart rate of less than 60 beats per minute. While an athlete’s heart rate may slow some as they gain fitness, a very low heart rate at rest (especially under 50) may be a clue that there is more to the story. Excluding other serious causes of bradycardia, there are two scenarios that are the most common to explain a slow heart rate in an athlete– an athlete’s heart vs. a starving heart. An athlete’s heart is one in which their training has resulted in a stronger, more powerful heart muscle. This means that the heart can pump out more blood per beat and so it can beat less frequently and still circulate the same amount of blood per minute. With many athletes training with heart rate monitors, they may notice that with training their heart rate at rest has decreased AND their heart rate during aerobic exercise may no longer rise as high for the same activity and effort.
On the other hand, an athlete with RED-S may over time develop a starved heart with bradycardia at rest but relative tachycardia (or a fast heart rate) with basic movements such as walking or even standing. In an athlete with RED-S, the body will eventually enter into an energy conservation state. One major way to conserve energy is to slow down your resting heart rate. In addition, a body that is not getting enough fuel will eventually resort to breaking down muscle for energy. As the heart is a muscle, we can actually see by cardiac imaging that the muscular heart wall may thin as nutritional deficits increase. While an athlete (and often the health care professionals that they see) may perceive this slow heart rate to be a sign of good fitness, it may be actually a sign of energy conservation. Without imaging the heart, an athlete’s versus starving heart can often be distinguished by measuring an athlete’s heart rate at rest and then measuring it while the athlete is walking. A starving heart will often demonstrate a 75% (or sometimes more) increase in heart rate with just walking. Athletes that wear heart rate monitors during exercise may also start to notice that while their heart rate at rest is low, it goes much higher than it used to for the same aerobic activity. This also often translates to the same activity and effort feeling harder and more difficult to sustain.
For more information on amenorrhea and RED-S in athletes, check out Dr. Rosen’s prior blog articles and podcast appearance discussing these topics:
1. Amenorrhea in the Female Athlete: 8 Myths Debunked
2. RED-S: A More Comprehensive Term for the Effects of Low Energy Intake in Athletes
3. P..H.I.T. for a Queen: A Female Athlete Podcast
4. Health Myths of the Female Athlete | Myth 3: Female Athlete Triad
5. Health Myths of the Female Athlete | Myth 2: Oral Contraceptive Pills
6. Health Myths of the Female Athlete | Myth 1: Amenorrhea