Photo courtesy of Tcg3j
Tonight's lesson plan for aikido class was to work on shikaku, the dead angle. The idea of shikaku is that tori is safer when standing behind or to the outside of one of uke's arms. Despite its importance, shikaku is not an advanced concept; every technique of hanasunokata places tori behind uke's arm..
In shikaku it is important for tori to control the near arm (usually at the elbow) because the elbow is a particularly effective weapon for uke and because the posture of the shoulder and elbow controls the posture of the rest of the body to a large degree.
The chain of the night was to work on the gaeshi-hineri and tenkai kote gaeshi relationships surrounding release #4 because these provide a lot of interesting exercise in getting into and maintaining the shikaku relationship while affecting uke's balance and damping his potential for harm. The cool technique of the night was aikinage because this is THE cool shikaku technique.
[Update February 2010 - The only thing that I'd think to add to this lesson is, when practicing the gaeshi-hineri loops associated with release #2 and release #4, it is important (vital?) to move to the end of the line (as far down uke's arm as possible) any time you are switching from omote to ura or vice versa. So, these loops tend to go osmething like, "behind - move away - in front - move away - behind - move away - in front ..." In some sense, you can treat the down-the-line condition as shikaku because you've moved to a dead zone of sorts - a place where uke can't effectively exert against you without moving.]