These days where almost everybody (depending on the country and the characteristics of it's league) is engage with their own preseason, I wan't to show you an article that has been published in Spain last year 2011, in which you can find some data of a professional spanish team where I have been involved some years ago, that talks about how the week load of the team can be measured (in this case using a GPS System), and how this load changes depending on the model of your training week or microcicle, and evidently on the short of tasks that you propose on the training.
It goes without saying that implication of players and other aspects of their emotional - volitional and socio - affective level also condition their physical demonstration.
In this case it's in spanish. For further explanation just let me know.
Enjoy

Lapuente 2011 Control de la carga semanal en futbolistas profesionales mediante tecnología GPS