OK, the answer is relevant to all TGs.
More TG_Fitness points means more training. More training means better improvement, but also more injuries. So let me take the obvious cases:
1. Using Cross Country instead of Weight Training, may make a positive difference for the players' physical attributes, without increasing injuries significantly.
2. .....may increase injuries significantly without making any difference to the players' improvement,
3. ....may not have any significant effect on either improvement or injuries.
4. ....may increase both improvement and injuries.
Now, the situation you are going to have to face depends on your team, your players, the details of your training schedule, and luck. Obviously, case 1 is good, case 2 is bad, case 3 is boring, and case 4 is the whole point of CM training (you 'll have to decide on where to draw the line- BTW, the dotted line in the diagram does not mean anything).
So your question is indeed simple, but the answer is quite complicated. That's the beauty of it, I guess. Let me know if you need any more explanation on this.