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Teaching Circulatory Responses to Exercise Using a Classic Paper by Grimby et al.

The circulatory system must respond to the increased muscular demand for oxygen and nutrients during exercise. Here we describe our didactic approach to convey how these adjustments are achieved using the classic paper by Grimby and colleagues published in J Appl Physiol in 1966. This paper is an ideal vehicle to do so because of the comprehensive battery of tests and the integrative nature of the experiments. Following the discussion on the tight matching between metabolism (oxygen consumption) and systemic blood flow (cardiac output), factors acting to increase oxygen consumption during exercise will be illustrated using the Fick equation and the ohm's law. Because stroke volume was measured in both supine and sitting positions and heart volume was also obtained, the importance of preload or venous return on augmenting stroke volume is discussed. The students can also develop appreciation for the automated acquisition of hemodynamic measures in modern laboratory since each sample was analyzed using the time‐consuming traditional procedure (eg, Douglas bag combined with the Scholander techniques for oxygen consumption). Finally, as the data were obtained in middle‐aged and older well‐trained adults and the data on young adults previously reported are also included, declines in aerobic capacity with age and the mechanisms underlying such decline can be discussed using the Fick equation.