Aerobic (or endurance) training improves your cardiovascular endurance (and thus your ability to run longer) by increasing both maximal cardiac output and your muscles ability to extract oxygen from the blood. Thus, a beginner running program designed to improve your cardio endurance must overload your circulatory system and challenge the oxidative capacity of your working muscles.

As with all running programs, specificity is crucial. If you are a runner and want to improve your aerobic endurance, then you need to run – not bike or swim. Likewise, if you are a cyclist who wants to become more proficient at biking up hills, then that’s where you need to spend more of your training time.