Hey guys just thought Id add my two cents.
Ive had some experience with GPS during my university studies and I found they are not only good measuring tools for distance and velocity but that some models can also measure other unseen variables such as body load.
During an internship with the Canberra Raiders I also noticed that they were having successful results by retailoring their recovery programs for players that had undergone more fatigue than others. One important thing they found was that measurements such as body load or even measures as simple as distance and velocity were not as accurately measured by the naked eye as they had once thought. And when I had last talked to one of their strength and conditioning coaches at a recent conference he was pretty sure that GPS technology was the future in fatigue measurement, and one of their most valuable tools.