Keep it at normal. Training harder is not worth it.

As stated above, increasing training intensity increases the chances for injury and lowers energy. At maximum training intensity, you gain 6 training points. This means that you'd have to train at maximum for 17 weeks for a player to gain enough extra training points to increase a skill 1 point. To make it even more useless, those training points are further divided depending on what area you train and whether or not you focus train. So you still won't actually gain an extra increase after this time, just enough total points that would have amounted to an extra increase if all the points were added to 1 skill.