How do you train a horse on horseisle to its max strength?

The strength training pen is in Appleton, on Horse Isle. Depending on the horse, it's maximum strength will vary. The training pen will give you +10 of strength, and you can train once every two hours (if you're a subscriber, you can train once an hour). The stats do decrease -1 every day, however, so make sure to train regularly.

Once the pink stuff is at the top of the maroon brackets, the training is complete.