Completing horse training

[FTL]

I've been training one of my Arabians, and I've nearly finished training a few of her stats, but I can't work out how I get the last few percent?

I've focused on completing her Balance training; however I cannot find any options that increase the balance stat that do actually increase it now? Anyone know why or can help me on how to do it?

This is the horse I'm talking about:

Chained for an Admiral


Thanks

[FTL]

I worked it out the level of fatigue prevents skill gain, the higher it is, the less skill gain