Knes 303 lecture 9 prescription of. Using heart rate (hr: why using hr to monitor and prescribe exercise, there is an apparent linear relationship between hr and vo2, also, cheaper because we have a lot more access to. Hr data and hr monitors can be done all the time and can be done at a lower cost. O2 supply is increased (at least in part) by increasing hr. Increases in cardiac output (co) are mainly due to increases in hr. In order to increase the oxygen supply, need to increase o2 delivery, and to do that you need to increase co. If you ask a person to exercise at 162 b/min, you assume their. Vo2 will be 3. 5l/min, but we know that it is an artifact and this linear increase is not always seen (especially when its not incremental exercise).