Power vs. Duration respectively Speed vs. Duration analysis have a long history in sport science.
Power-Duration relationships have become very popular and also very useful in managing training & performance in endurance sports - particularly in cycling. It provides a relatively easy way to get an idea of the performance of an athlete.
Besides a significant amount of knowledge and scientific data on this topic, the physiology behind the power duration relationship seems to get little respect in its application to training. As a consequence, benchmarks such as critical power and moreover W' are often misused and misinterpreted.