Jared Tucker and Dr. Larry Tucker, Physical Education
INTRODUCTION
Heart disease has been the leading killer in America for almost a century.1 Currently, heart disease takes the life of nearly one in every three Americans.2 Because of the epidemic proportions of heart disease, research directed at preventing this serious problem continues to expand.
The American Heart Association has identified five modifiable risk factors associated with heart disease: hypercholesterolemia, smoking, hypertension, obesity, and sedentary living.3 Hypertension (high blood pressure) is considered one of the most serious of these risk factors because it is a “silent killer.” In short, many Americans do not know they have high blood pressure because there are no apparent signs or symptoms.4
Hypertension affects about 25% of the adult population in the United States.5 Although most cases of hypertension are considered idiopathic, there are a number of factors that influence blood pressure, including race, age, smoking, body weight, alcohol use, stress, diet, and physical activity. Because physical inactivity, like hypertension, is one of the five key causes of heart disease, the relationship between these two risk factors has generated increased interest in recent years.
The association between chronic physical activity and blood pressure is difficult to evaluate for several reasons. First, valid and reliable measures of usual physical activity are rare. Most researchers use self-report methods, such as surveys and questionnaires, to assess typical activity patterns. These methods are subject to exaggeration and wishful thinking among adults.6 Second, because even the slightest exertion influences blood pressure, complete rest for at least 15 minutes is required before accurate measures can be taken.7 Third, because blood pressure fluctuates widely throughout the day, multiple measures across multiple days are required to index true resting blood pressure.7 As a consequence of these challenges, few researchers have investigated the relationship between chronic physical activity and resting blood pressure using high-quality measurement methods.
The purpose of the proposed investigation is to overcome the shortcomings of past research by using high-quality measurement methods to study the true association between chronic physical activity and resting blood pressure.
METHODS
Subjects: A total of 280 middle-aged women from the Utah Valley area were used as participants in this study. All participants signed an informed consent document, approved by BYU’s IRB, before participating in the study.
Procedure: Subjects were asked to report to the Human Performance Research Center in 127 Richards Building. After the study was explained and subjects completed the informed consent requirement, they were asked to remain sitting while reading for 15 minutes. After 15 minutes, blood pressure was measured three times using a calibrated mercury sphygmomanometer and a medical stethoscope. Each blood pressure measurement was followed by a 60 second recovery period before the next reading was taken.
To reduce measurement error inherent in self-reported physical activity, the present study used Computer Science and Applications (CSA) accelerometers to measure the actual daily physical activity performed by participants. CSA accelerometers have been shown to be valid and reliable measures of physical activity.8-10 Each subject wore a CSA accelerometer, which was fastened securely around the waist at the level of the umbilicus and positioned over the left hip. Each subject was asked to wear the accelerometer continuously for seven consecutive days. Subjects were asked to remove the accelerometer only when bathing or during activities in which the monitor might become wet.
Activity counts were downloaded from the CSA monitors and used to index physical activity. Activity counts were stored in 10-minute intervals (epochs) continuously. Hence, there were 144 activity count measurements for each day and 1008 activity counts over the test week. The 1008 total activity counts were summed to generate one total physical activity score. Each subject was asked to report to the lab the day after wearing the accelerometer to return the monitor and to have blood pressure measured again. As before, subjects sat and read for 15 minutes before blood pressure was measured three times with one minute recovery periods between readings. The average of the three blood pressure readings taken on each of the two testing days (six total readings) was used to index blood pressure.
Results
Subjects were divided into three groups based on their physical activity level (from lowest to highest). Average blood pressure values for each group (+SD) were as follows: Systolic blood pressure: 108.5 (+9.3), 107.9 (+10.3), 108.8 (+9.5); Diastolic blood pressure: 73.4 (+7.4), 72.6 (+8.3), 73.7 (+6.6). There were no significant differences between resting blood pressure values among any of the physical activity groups both with and without controlling for potential confounders.
Conclusions
Results from the current investigation suggest that resting blood pressure is not related to physical activity levels in middle-age women. However, these findings are not consistent with most of the current literature which suggests that physical activity is negatively correlated with blood pressure. A possible limitation of the current study may include the fact that the majority of subjects had relatively low blood pressures. Therefore, if physical activity only helps to decrease blood pressure among those who are hypertensive, no results would be seen among subjects with healthy blood pressures, such as in the current investigation. In conclusion, additional research using adults with higher levels of blood pressure needs to be conducted to fully understand the relationship between physical activity and blood pressure.