What is “RPE” and why does Hiiro use it for training?

RPE (Rate of Perceived Exertion) is a 1–10 effort scale where 1 is being stationary and 10 is running all-in. It is subjective to you and your perception of difficulty. Hiiro uses RPE because everyone’s heart rate zones and paces are different, so what is optimal for one can be way too hard or easy for another. RPE lets keep load personalised and therefore runners can train most efficiently and reach their optimal result.