Cardio load is based on training impulse calculation (TRIMP), a commonly accepted and scientifically proven method to quantify training load. Your Cardio load value tells you how much strain your training session put on your cardiovascular system. The higher the Cardio load, the more strenuous the training session was for the cardiovascular system. Cardio load is calculated after every workout from your heart rate data and session duration.
Your cardio load from a single session is shown in the summary of your training session on your watch, in the Flow app and in the Flow web service. The higher the cardio load, the more strain it caused to your body. In addition, you can see a visual bullet scale interpretation and a verbal description of how hard your cardio load from the session was compared to your 90 days cardio load average.
The scale of bullets and verbal descriptions adapts according to your progress: the smarter you train, the higher loads you tolerate. As your fitness and tolerance for training improves, a cardio load that was ranked worth 3 bullets (Medium) a couple of months ago, could rank for only 2 bullets (Low) later on. This adaptive scale reflects the fact that the same kind of training session can have a different impact on your body depending on your current condition.