University of Texas Southwestern Medical

¶ … University of Texas Southwestern Medical Center in Dallas studied the effects of exercise on the decline in physical conditioning associated with aging. The study was an extension of a study done in 1966, that of the Dallas Bed Rest and Training Study. The study used five men from the original study, now ages 50 to 51. Of the five, only two were still participating in an exercise program regularly. All reported weight gain and an increase in body fat since the original study. In this extension of the study, the men participated in various individualized endurance training programs, including walking, jogging, and stationary bicycle riding. Their endurance training was increased weekly, and the results were analyzed. The research design was that of a quantitative experimental design, examining the causal relationship between increased exercise, age, and cardiovascular response.

There are some main strengths of this study. First, the use of subjects originally studied 30 years ago negates any possible negative effect of experimental mortality on the internal validity of the study. By using the same subjects 30 years later, the results of the study are more casual in nature, since there is no question of how these subjects differ from those studied previously.

Secondly, the use of randomization to the experimental groups reduces the threat of bias. Each of the five subjects was randomly assigned (we assume) to a particular exercise activity. By randomly assigning the subjects, the researchers reduced the likelihood that the noted effects of the exercise was biased based on the personal choice of the subject. Additionally, random assignment to groups helps the researchers to avoid personal bias when interpreting the results.

A third strength is the data from the original study. By comparing the data from this portion of the study to the data collected in the first phase of the study, it was possible for the researchers to gain a better understanding of the long-term effects of exercise on the body. Since longitudinal studies are rare, and since a loss of subjects over time is common, the use of the original data in combination with the same subjects helps to ensure the internal validity of the study,

There are some definite weaknesses of the study however. First, there was no control group. Since the point of a control group is to minimize the risk of placebo effect on the internal reliability of the study, this is a major weakness. Without some form of control group, it is unclear whether or not the change in cardiovascular response and adaptation found in the study was actually caused by the increased activity, or by something else.

Furthermore, the subject pool in this study was extremely small. Without a larger subject base, it is again more difficult to prove a causal relationship. Additionally, the lack of a control group and of such a small subject pool is a threat to the external validity of the study. Without a broader range of subjects, the researchers cannot justifiably generalize the findings of the study to the everyday settings of real life.

Since the experiment was very personalized, with a regimented exercise program, it is already difficult to generalize the results to the wider population. Since the subjects were well aware of the point of the study, there is a possible risk of reactivity on their part, such as more dedicated effort in the exercise program. Additionally, since it is assumed that the subjects were not continuously monitored, their knowledge of the point of the study may have affected outside variables that may contribute to an improved cardiovascular response, such as eating habits, and other exercises.