  In this paper it is performed the comparative biomechanical analysis of the
Kuzushi (Unbalance) -Tsukuri (the entry and proper fitting of Tori's body into
the position taken just before throwing) phases of Judo Throwing techniques.
The whole effective movement is without separation, as already stated by old
Japanese biomechanical studies (1972 -1978), only one skilled connected action,
but the biomechanical analysis is able to separate the whole in didactic steps
called Action Invariants. The first important finding singled out is the
existence of two classes of Action Invariants the first the General one'
connected to the whole body motion is specific of shortening distance in the
Kuzushi Tsukuri Phase. The second one, the Specific Action Invariants is
connected to the superior and inferior kinetic chains motion and right
positioning connected both to Kuzushi and Tsukuri phases. Some interesting
findings derive from this analysis: among throwing techniques, couple
techniques could be independent from Kuzushi; instead physical lever groups
need all two action invariants to be performed successfully and as complex
motor skill they are more difficult to perform than the first ones. Complexity
in motion is connected to the energy consumption, and to the skill ability of
athletes. This biomechanical comparative analysis is useful from the didactic
point of view, clarifying the basic mechanical steps of all throws, and showing
also hidden connections, similarities and differences among throwing Judo
techniques. The last part of the paper concerns the study on Interaction in
Competition, performed by the author, showing 20 years results on Judo
Biomechanics.
