This white paper describes the scientific background of Polar Training Load Pro, its functions, and validity.
Polar Training Load Pro holistically consists of three loads, including Cardio load, Muscle load and Perceived load. Cardio load is calculated based on training impulse and shows the cardiac response to a training session. Muscle load shows the amount of mechanical energy (kJ) that was produced during a running or cycling session and is the product of average power and duration of the training session. Perceived load is calculated from training duration and the subjective feeling of the user. All loads are given in absolute numbers and are also expressed as bullets and text reflecting how hard a training session was compared to the user’s average training session load from the past 90 days. Training Load Pro also displays Strain and Tolerance. Strain describes how much the body has been strained recently and is calculated from the average daily Cardio load from the past 7 days. Tolerance describes the readiness to endure cardio training and is calculated from the average daily Cardio load from the past 28 days. Based on the ratio between Strain and Tolerance, Cardio load status and injury & illness risk are calculated. Cardio load status (= Strain divided by Tolerance) gives you an estimate whether your training status is detraining, maintaining, productive or overreaching. If you have been training more than usual, you have an increased risk of getting injured or sick and the application will alert you to this by giving an injury risk alarm.
Calculations of Cardio load, Muscle load, Perceived load and injury & illness risk are based on scientifically accepted methods.Full document (PDF)