The sun is shining, there is a small breeze, let's tack your horse and start a nice walk. Soon enough you notice your horse is getting tired, sweating from the sun, you have to cancel or limit your long planned walk... So better have a look if there is a simple program/training to prepare your horse for a nice long summer ride. There are different trainings and excercises for different occasions. Basically if your horse is following a basic or advanced trainings program, there shouldn't be any problem to go for a long ride. However imagine your horse has been in the stable for a while (winter to summer) or on a field without a 'sportive' training. Then it might take a while to get your four-legged friend fit. Basically the best training is to maintain a fixed schedule where you ride your horse a minimum of three days a week. You best start with a 30 minutes ride and gradually, over an about four-week period, work up to 90 minutes per ride. Of course the timing always depend the pre-set goal you want to achieve with your training. For the first few rides just walk and trot in sequences of 15 minutes. Later you can add a canter and limit the walking time of your horse. Important is also that you learn your horse to adjust to its environment. If you are training for a trail ride then , by all means, ride him/her on the trails! TO conclude it is harder to get your horse fit than to keep him/her that way. Horses retain their condition much better than people do. Continue riding two or three days a week with continuous turnout all year long. And make sure to breath once and a while in the training...