Determining Your Training Zone with Breathing and RPE

Heart rate is a good indicator of your conditioning, the extent of stress you are experiencing, your current level of rest and the effects of heat, humidity and fatigue. While a heart rate monitor is a good tool for athletes to gauge their exercise intensity, it is not a necessary tool for the beginning runner. Your rate of breathing and perceived effort are also very useful to determine your intensity and more importantly if you are exerting yourself excessively. More importantly, focus on becoming consistent and staying comfortable during your runs. I would definitely recommend a heart rate monitor as a valuable tool for training, especially as you gain more experience, but you must be willing to learn how to use it as intended. Through a short search on Google, I found this good and very comprehensive guide.