AI generated summary:

Training load is a key concept in elite sport, and can be divided into external load (e.g., distance covered, number of repetitions, wattage) and internal load (the athlete’s physiological & psychological response to that external load).

The RPE (Rating of Perceived Exertion) is a subjective measure of internal load — i.e., how hard an athlete feels they have worked. It is simple, inexpensive, and applicable across various exercise modes (endurance, strength, interval).

Two commonly used scales are:
The classical Borg Scale (6–20) — originally developed to correlate with heart rate (e.g., RPE 13 ≈ HR 130 bpm).
The simpler Foster Scale (0–10) — where 0 = no effort, and 10 = maximal effort (useful in many sports contexts).

RPE is a low-barrier, practical tool to monitor internal training load. When applied within a structured monitoring system, coaches and athletes can gain valuable insights into load, the relationship between planned and actual effort, and potentially the factors contributing to injury, illness or sub-optimal performance.