Many people ask how to get horses fit for endurance riding. There are of course many different answers to this question as there are methods. My personal preference is to carry out 6 to 8 weeks of basic training at walk trot and canter then to introduce interval training.
Where you start from will also depend on what your horse has been doing previously for example you would not treat a horse that had had a three month holiday the same as one that had been ridden two to three times a week since the end of last season till January.
With a horse who has had a break I like to start it's fitness plan by walking for 15 minutes on the first day and building this by 15 minutes a day for 6 days then have a day off and the second week ride 6 times for about an hour and a half in walk trying to include as many hills as possible in our route.
For a horse who has stayed in work over the winter period I like to maintain the two to three days of ridden work at their current level and gradually introduce extra days work to a maximum of 6 days per week. With the extra days of work starting in walk for 30 minutes then the next extra day 1 hour etc.