exercise that is measured by how hard you FEEL you're exercising, not by heart rate. This is usually done on a scale of 1-10 with 10 being the hardest.

The subjective perception of exercise effort; see Borg’s scale (of perceived exertion).

A fancy way to say "how do you feel," i.e. how do you "perceive" your "effort?" Often measured on a 0-10 scale, with 0 being nothing and 10 being all-out activity.

The level of intensity you feel your body is exerting during exercise on a scale of 0 to 10. An unscientific way of staying within your target heart rate zone.

exercise is more accurately done on how hard you FEEL like you're exercising than it is on heart rates.