[QQQQQ-Trek]

Both the shinai and bokuto are derived from the katana but their different lengths are a reflection of their respective uses. The shinai is used in keiko and in tournaments where you are physically striking an partner/opponent and its length and weight has been standardized for such usage much like other sporting equipment is regulated. As Neil points though, the shinai's length is not without historic precedent for katana. The bokuto is used in kata and kihon waza where you are not physically striking your opponent but focusing on mental and physical nuances of kendo that support shinai techniques. Whether bokuto or shinai, maai is the important dimension, not the differing lengths between the two. Looking at chudan-no kamae, the relative positions of crossed shinai (usually somewhere below the sakigawa) and crossed bokuto (right at the yokote) will point out the difference in lengths but also the commonality of maai. Issoku-itto-no-ma is more an aspect of shinai waza rather than bokuto reiho, so it will differ according to each person in shinai practice whereas it is a set distance in kata or kihon waza practice. Still, the relative separation between partners at chudan is very similar whether using bokuto or shinai.