Different training systems were compared in research done at Cornell University. This chart compares a Y trellis with Slender Spindle and Central Leader, or free standing orchard system.  The Slender Spindle is onM.9 rootstock. The statistics for the Central Leader are divided according to rootstocks M.9/M.11 and  then M.7a.   The Y trellis rootstock is M.26.  The different rootstocks indicate that the trees are different sizes.  Therefore, there is a different number of trees per acre with each system. 

The trunk cross-sectional areas  or TCA, is a relative measure of tree size, meaning the larger the number, the larger the tree.  The TCA and cumulative yield of the trees were calculated after 10 years of growth. The Central leader of the M.7a rootstock has a larger trunk cross-sectional area simply because the tree rootstock is 10 percent larger then the M.26 rootstock on the Y trellis.  Despite the size of the rootstock or the TCA, the Y trellis has a higher cumulative yield then either of the other two systems. The cumulative yield of Slender Spindle comes in second, and the Central Leader system especially the system on the large M.7a. rootstock, is the least productive.