Here's the typical trainer's concern; it's believed that players outside of the top 100 have worries that a guy like Federer doesn't - i.e. travel expenses, points to defend and so on. Many of these players perform a concentrated physical prep block for 4-6 weeks in Dec/Jan (just prior to the start of the new season) and then a number of 1-2 week blocks during the course of the year. These same trainers will also agree that this isn't enough - performing one 4-6 week block along with 2-3 smaller blocks during the year is an insufficient amount of time to develop a quality like explosive power, for instance.
