One of the best places to see what can be achieved by training fruit are The Gardens of West Dean College near Chichester in Sussex www.westdean.org.uk.The gardens feature two restored kitchen gardens of the late Victorian period;the restoration is largely the work to Jim Buckland and Sarah Wain it has been beautifully done to the last detail.
General Principles of Training Apples and Pears
1.Horizontally trained branches are fruitful, vertical branches produce wood and not fruit much. With this in mind to fill the space to be trained vertical growth is encouraged, as the space is filled growth can be tied down to produce fruit.
2. Autumn is a good time to pull down vertical growth produced in the summer so that it will bear fruit buds the following year.
3.Summer pruning of established trained fruit reduces growth and encourages next years fruit. This because it shocks the tree by removing leaves and it exposes the wood to sunlight which initiates fruit bud.
4.Winter pruning will encourage growth so should only be used on young trees to fill the cropping space or to rejuvenate older trees where there is not enough vigour. Of course pruning can be employed at anytime to remove diseased wood especially canker,don't delay on this one.
5.Remember trained fruit can be developed into almost any shape you like although you might have read the gardening books and magazines the fruit trees havnt, they don't know the
difference between a cordon,espalier,palmette,fan,goblet,or a pyramid.And don't forget tripovers or are they called stepovers.