The Cooper Institute

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH


Can Being Fit Decrease Your Risk of Sudden Cardiac Death?

Posted in

Wednesday, Aug 08, 2018

Sudden cardiac arrest (SCA) is a condition where the heart muscle suddenly stops beating unexpectedly, often leading to sudden cardiac death (SCD). This is not the same thing as a heart attack. The American Heart Association tells us that it’s helpful to think of a heart attack as a ‘circulation problem’ whereas SCA is an ‘electrical problem.’ While 70% of heart attack victims survive, only about 10% of SCA victims are as fortunate. Although SCA can affect both men and women, for unknown reasons it is much more likely to affect men. Little else is currently known about the risk factors that could help predict SCD.

Over the past half-century, numerous studies from The Cooper Institute have shown that having a moderate to high level of cardiorespiratory fitness (CRF) significantly decreases the risk of death from heart attack, stroke, and heart failure. However, very little is known about the association between CRF and SCD.

Study Results:

Researchers studied over 55,000 people (41,949 men and 13,507 women with an average age of 44 years) who underwent a comprehensive physical examination at the Cooper Clinic. This baseline examination included a maximal treadmill exercise test, which is the gold standard measurement of CRF. Based on their age and sex, subjects were assigned to the low fit (bottom 20%), moderate fit (next highest 40%), or high fit (highest 40%) category. The entire group was then followed for an average period of 14.7 years, during which time there were 109 SCD’s.

When analyzing the data, researchers carefully took several factors that might have muddied the waters into consideration. These included age, body mass index (BMI), smoking, family history of cardiovascular disease, and abnormal electrocardiogram, as well as the presence or absence of hypertension and diabetes. In Figure 1 below, a comparison of the risk for SCD is shown across low, moderate, and high CRF categories after taking all of the previously mentioned factors into consideration. When compared to low fit men and women, those who were moderately or highly fit were 44% and 48% less likely to  experience SCD during the follow-up period, respectively.


Researchers also examined the risk of SCD in hypertensive versus normotensive, and normal weight versus overweight and obese* individuals across the 3 levels of CRF and found similar results. This is shown in Figures 2a and 2b below.

In Figure 2a, we see that among normotensive men and women, the risk of SCD was reduced by 38% and 51% in those who were moderate or high fit, respectively when compared with the low fit normotensive group. Among hypertensive men and women, the risk of SCD was reduced by 65% and 72% in the moderate and high fit groups, respectively when compared with the low fit hypertensive group.

In Figure 2b, we see that among normal weight men and women, the risk of SCD was reduced by 43% and 58% in the moderate and high fit groups, respectively when compared with the low fit group. Among overweight and obese men and women, the risk of SCD was reduced by 58% and 64% in the moderate and high fit groups, respectively when compared with the low fit group.  

These results show that having a moderate to high level of CRF is significantly associated with a reduced risk of SCD in general, as well as in those who are normotensive, hypertensive, normal body weight, or overweight/obese.

Like all research studies, this one had its strengths and limitations. Strengths included a very large sample size, accurate measurement of CRF, BMI, and blood pressure, a long follow-up period, and clear documentation of the 109 cases of SCD. A limitation of Cooper Clinic data is that the sample is composed primarily of white men and women. Thus, it is unknown if these results extend to non-white populations.


Time is critical. While SCA results in SCD in about 90% of cases, medical experts tell us that the odds of survival are much greater if the victim begins receiving CPR within a minute or two of the arrest. The odds of survival improve much more if an automated external defibrillator (AED) is used. Sadly, only a small percentage of individuals who experience SCA receive CPR/AED intervention prior to arrival of emergency medical services. For the rest, it’s sometimes too late by the time the ambulance arrives. Is your CPR/AED training up to date?
*A normal weight in adults is defined as a body mass index (BMI) of 18.5-24.9 kg/m2, while overweight and obesity are defined as a body mass index of 25.0-29.9 and >30 kg/m2, respectively. Use this link to calculate your BMI.


American Heart Association. Heart attack or sudden cardiac arrest: how are they different? September 19, 2016.

Jimenez-Pavon, D., Artero, E., Lee, D., Espana-Romero, V., Sui, X., Pate, R….Blair, S. (2016).

Cardiorespiratory fitness and risk of sudden cardiac death in men and women in the United States. Mayo Clin Proc, 91(7):849-857.

Note: Did you know that The Cooper Institute is one of only a handful of organizations that has a nationally accredited Personal Trainer Certification? If you have a passion for health and fitness and enjoy working with people, or if you are already working as a personal trainer, click here to learn more about the CI-CPT (Cooper Institute Certified Personal Trainer)!  We have many resources that can assist you.