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Stage IV, The left-foot-step-forward throw with trunk rotation and
horizontal adduction in the arm's ‘forward swing. This throw is the
mature throw (Type VI) and is found in all boys from 6% years up. Most
of the girls from 65 years - au this form but with arm movements
incompletely developed (Type V).
4, The outstanding trend disclosed by the movement types is change from move-
ments in the antero-posterior plane to movements largely in the horizontal
plane.
5, The outstanding trend disclosed by the timing features is a progressively
shorter period of acceleration and an earlier release, This trend attends the
change in movement types.
6. Overlapping of features into chronologically adjacent types demonstrates
emergence of one stage into the next,
7. Comparison of the girls' performances with boys performances indicates
sex similarity in the basic growth pattern of the age and sex differences in
the performance level of that pattern.
8, Evidence suggests that the arm action is largely responsible for the speed
imparted to hand and ball,
9, The average acceleration per second throughout the interval from the be=
ginning of the forward swing to the release ranges from 18 feet to 1200 feet.
10. Four means of evaluating the throw have been diversely arrived at:
1) velocity of the ball, 2) movement performance score, 3) timing score,
4) acceleration of the hand with ball, Relationships between ranks assigned
to these evaluations and to age expressed in rank order intercorrelations
range from +. 81t,043 to +.95%,012 for the entire group; from +.83%,055 to
+.98,007 for the boys! group; and from +,77%,072 to +,956,017 for the girls'

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