UPDATE: An article in the Nov. 24, 1988, issue of the New England Journal of Medicine by Dr. Lars-Goran Ekelund and colleagues has shown the level of physical fitness to be an independent and important risk factor for cardiovascular disease.
These researchers screened a large group of people involved in the Lipid Research Clinics prevalence survey and selected 4,276 men whose blood cholesterol levels were above 240 mg/dl as subjects. Each subject was then tested on a treadmill to determine fitness levels as shown from the heart rate in stage two of the fitness test and the total amount of time the person stayed on the treadmill as both the speed and grade were increased. Many of these men tested positive for cardiovascular disease during the exercise test and were placed into another study because of their current health status.The remaining healthy subjects (3,106) were then assigned to four groups based on their fitness level from low fitness to high. The mean heart rate during stage two in group I (high fitness) was only 112. Group 2 was 127; group 3, 139; and the lowest fitness group required 156 beats per minute at that same level.
All of these men were followed closely for an average of eight and a half years. During that time, 45 fatal cardiovascular events occurred in the healthy group, and the mortality from cardiovascular disease was eight and a half times higher in the lowest fitness group from that in the high.
Higher fitness levels in previous studies have been associated with the change in the total risk-factor profile (i.e., lower levels of total cholesterol, LDL cholesterol and triglycerides and higher HDL, etc.). However, when other risk factors were controlled statistically, there was still a significant relationship between physical fitness and death from cardiovascular disease, independent of these other factors.
Several questions are raised as a result of this study. First, is the higher fitness as measured on the treadmill a reflection of activity levels or genetics factors? In this study, the fitness levels correlated well with physical activity as reported on an activity questionnaire. This means that activity was the most important factor in reducing the risk from cardiovascular disease.
The other questions have to do with why fitness is helpful. Several studies may help suggest reasons. For instance, one study showed that physical training produced an increased threshold for ventricular fibrillation in isolated rat hearts. This change may help a person tolerate arrhythmias or decrease the number of events leading to arrhythmias.
Other studies show an increase in the amount of oxygen available to the heart as a result of activity. This would allow the heart to function more effectively and more safely at any given work load. Even the aggregability of platelets (clotting) is decreased with exercise. This means the chance of blockage in a narrowed coronary artery would be reduced.
Whatever the effect, exercise is surely important in terms of your health, and you should consider beginning a program if you are not already involved.