I guess you mean the training you use during the season.
I think it is better to make special fitness ones. I've done it in FM12 and the difference in the start of the season can be noticed, I've for the first time seen the team perform from the start, which I rarely saw before unless my team was the strongest by some distance.
I also see the difference in FM12: during the preseason, with fitness focused schedules, my players get fit with two matches (no more than 60 mins each for any player) and with three or four friendlies I get all the squad match fit and able to take two weeks without losing the status without playing, whereas during the season they need more than two reserve games to gain match fitness from a similar starting point and they lose it faster. Unless they're the players I keep with high fitness training.