TrainingPeaks, Training Stress Score explained

Vendor documentation defining Training Stress Score (TSS) and the Performance Management Chart, where Chronic Training Load (about a 42-day weighted load) stands for fitness, Acute Training Load (about a 7-day load) for fatigue, and their difference for form. These are modelled estimates built on the Banister fitness-fatigue framework and fixed time constants, not measured physiological loads: equal TSS from easy volume and from hard intervals does not represent equal biological strain. Strong as a description of how the metric is constructed; the construct itself is a model.