—Differences in hemodynamic response between upright and supine positions were considered when the data were collected by us in the 1984 study.1 Treadmill performance (Bruce protocol) was chosen to calculate the maximal exercise values because it is commonly used in US cardiology. We additionally determined progressive exercise to maximal performance using a bicycle ergometer in supine position. In our opinion, however, further comparison of results to this less common work-performance protocol would have unnecessarily complicated the article.
We do agree with Drs Margulis and Katz that the differences between trained and untrained subjects and between healthy subjects and coronary patients must be considered. Only healthy subjects were included in our study, however, and fitness was not a selection criterion. In fact, we reported a wide range of fitness among the healthy subjects that, in turn, makes the results more generalizable to the population at large than if based