The Cooper Institute
 

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

 
 

How Does Being Sedentary Hurt Your Heart? New Insights from the Cooper Center Longitudinal Study

Posted in

Tuesday, Feb 20, 2018


It has long been known that there is a strong and independent association between low levels of cardiorespiratory fitness (CRF) and various types of cardiovascular morbidity and mortality. Some of this association is thought to be due to the favorable effect of exercise on coronary risk factors. For example, back in 1976 Dr. Kenneth Cooper  was the first to show that higher levels of CRF were associated with improved levels of resting blood pressure, blood cholesterol, triglyceride and glucose levels, as well as body weight and percent body fat. Later research showed that higher CRF was also associated with improved insulin and Hemoglobin A1C levels. However, the beneficial effects of higher CRF levels on risk factors do not fully explain the association with lower risk of cardiovascular disease (CVD).  

Cardiac troponin T (CTT) is a protein that is found in the heart muscle, and is released into the bloodstream when heart muscle damage occurs. Such damage would occur when a person has coronary artery disease, congestive heart failure, or other significant heart health issues. Higher blood levels of CTT in patients with existing cardiovascular disease are associated with a higher risk of death. Recently, a highly sensitive blood test for CTT has been developed, meaning that very low CTT levels can now be detected in members of the general population who have no symptoms. Low levels of CTT indicate minor, subclinical heart muscle injury that could otherwise not be easily detected. Perhaps part of the link between low CRF and increased CVD morbidity/mortality might be due to higher levels of CTT in low fit individuals. Since this issue had not been examined previously, Cooper Institute researchers were excited to take a look at it.   

Thus, the purpose of this study was to examine the association of CRF with CTT in middle-aged to older adults. The hypothesis was that higher levels of CRF would be associated with lower levels of CTT. The sample consisted of 2498 apparently healthy Cooper Clinic patients with a mean age of 58.7 years who underwent a comprehensive preventive exam between 2008 and 2012. Blood was drawn prior to their treadmill exercise test. Based on the results of their treadmill test, subjects were placed into 1 of 5 CRF categories (quintiles). Subjects were classified as low fit (quintile 1), moderate fit (quintiles 2-3), or high fit (quintiles 4-5) according to their age and sex.

As shown in Figure 1 below, there was a significant inverse trend between CRF and CTT levels; with average CTT values of 7.8, 7.00, and 6.0 ng/L in low fit, moderate fit, and high fit groups respectively. 



In Figure 2 below, we show the prevalence for various ranges of CTT across CRF categories. The blue shaded areas represent the prevalence of low levels of CTT, while the green, black, and red shaded areas represent the prevalence of moderate, high, and very high levels of CTT, respectively. Starting with the blue shaded areas, we see that the prevalence of low CTT increases across increasing levels of CRF. Numerically speaking, only about 10% of those with low CRF had low CTT levels, while about 22% of those with high CRF had low CTT levels. At the other end of the spectrum, when we look at the red shaded areas, we see a decreased prevalence of very high CTT levels across increasing levels of CRF. Numerically speaking, about 12% of those with low CRF had very high CTT levels, while only about 2.5% of those with high CRF had very high CTT levels. So in other words, the various ranges of CTT look consistently more favorable across increasing levels of CRF.   


Because of the association between CRF and CTT, Dr. DeFina and her colleagues concluded that low CRF may be related to minor, subclinical myocardial injury. It is important to note that because of the cross-sectional nature of this study, cause and effect cannot be proven, and it is not possible to determine which comes first, low CRF or elevated CTT. Further research is needed in order to determine whether improving CRF will lead to decreased levels of CTT, which would suggest decreased subclinical heart muscle injury. In the meantime, all adults should strive to meet the current public health guidelines for physical activity by accumulating a minimum of 150 minutes per week of moderate intensity aerobic activity and by performing a minimum of 2 days per week of resistance training.  

Reference
DeFina, L.F., Willis, B.L., Radford, N.B., Christenson, R.H., deFilippi, C.R., de Lemos, J.A. (2016).  Cardiorespiratory fitness and highly sensitive cardiac troponin levels in a preventive medicine cohort.  Journal of the American Heart Association, 5(12).  DOI: 10.1161/JAHA.116.003781




Note:
The Cooper Institute has recently published a state of the art textbook titled Principles of Health and Fitness for Fitness Professionals. This book is an absolute must for fitness leaders or anyone in the general population who wants to learn more about health and physical fitness. The book is also a great resource for anyone who is seeking to earn a nationally accredited personal trainer certification! Click on the links above to learn more.

 

 [FS1]Hyperlink to January CCLS blog