Editorial Exercise and the Circulation RECENT INTEREST in the response of

the circulation to muscular exercise has stemmed from apparent discrepancies in the literature concerning the relative importance of changes in heart rate and stroke volume, from controversy as to whether conclusions drawn from the behavior of the Starling heart-lung preparation can be applied to the intact organism, and from studies that have attempted to define the coordinating role of the central nervous system. It is now well established that in man dif-ferent views coneerning the contribution of stroke volume stem, not from faults in meth-odology, but from differences in the posture of the subjects in the various studies. ' Thus, when the subject is in the supine position, the stroke volume at most is only 10 to 20 per cent greater during leg exercise than at rest.2 3 When the subject is standing relaxed the heart rate is greater and the cardiac out-put less than in the supine position; hence, the stroke volume is considerably reduced, sometimes by as much as 50 per cent. With mild exercise in the upright position, such as marking time, the stroke volume increases to approach or to equal that in the resting su-pine position, but with increasingly severe exercise there is only a slight additional in-crease in stroke volume, even when the car-diac output exceeds 20 liters per minute and the oxygen consumption is about 3 liters per minute.3 ' 4 Few data are available concerning the re-sponse in trained athletes, despite the popular notion that their stroke volume greatly in-creases duringf severe exercise. Bock and colleagues,5 however, showed that the pattern of response in a marathon runner was quali-tatively similar to that of untrained men, although values for stroke volume were con-siderably greater both at rest and durin