RPE rate of perceived exertion
Tracking your heart rate — either with a heart-rate monitor or by taking your pulse — allows you to continually adjust your workout intensity. However, the equation used to calculate your optimal training zone is far from perfect, and the traditional formula used to find your maximum heart rate (220 - your age) was found to underestimate MHR by as much as 40 beats per minute, especially in athletic people.
A better way to train, especially if you’re more experienced, is intuitively by using the rate of perceived exertion. While it won’t pinpoint your exact intensity and output, it’s a solid way to self-assess how hard you are working — i.e., your “perceived exertion.” The idea is to work within the correct range based on your exercise goals.
10 Max Effort — Out of breath
9 Very Hard — Can barely breathe
7-8 Vigorous Activity — Short of breath
4-6 Moderate Activity — Breathing heavily
2-3 Light Activity — Easy to breathe
1 Very Light Activity — Hardly any exertion