Rate of Progression for Exercise

according to the american college of sports medicine, cardiorespiratory fitness and improvements in the abliity of the heart to deliver oxygen to the working muscles results in increased endurance performance. also, the greatest improvement in cardiovascular endurance occurs when exercise involves the use of large muscle groups over prolonged periods of time (running, in your case). therefore, you are currently doing an exercise that will truely results in cardiovascular endurance in the long run. the proposed rate of progression in an certain exercise depends on many factors. for apparently healthy adults, which now that you've quit smoking, you seem to be, the endurance aspect of the exercise has three stages: initial, improvement and maintenance. you seem to have completed the initial phase, so the next phase is improvement. this stage usually lasts for 4 to 5 months, during which the intensity and duration are increased every 2 to 3 weeks until you are able to exercise at a moderate-to-vigorous intensity for 20 to 30 minutes continuously. with this said, you can see that adding more miles to your run is not the only way to increase endurance. actually, by slightly increasing both intensity and duration, you will see faster, more signifigant results. congratulations on nixing the smoking habit!!