FTP is the maximal running pace an individual can sustain for an effort of approximately 45 - 60 min in duration. Here's how to determine your FTP.
Calculating your Run Training Stress Score (rTSS) for running is a useful tool for coaches. This article explains what rTSS is and how it is calculated.
The most useful tools to quantify how hard you're training are those metrics that account for both the volume and the intensity of your running. A systematic approach to quantifying training load that integrates both volume and intensity is the training impulse or TRIMPS system.
Normalized Graded Pace (NGP) is defined and explained by the creator of its algorithm, Stephen McGregor.