Table 5. Kinematic measures computed over the 3-D body joint data for activity recognition, and corresponding equations.

Measure	Joints	Equation
Velocity	Head, neck, spine middle, spine base, and spine shoulder	(1)
	Shoulder, elbow, wrist, hand, hip, knee, ankle, foot, hand tip, and thumba
Z-axis velocity	Head, neck, spine middle, spine base, and spine shoulder	(2)
Distance between symmetrical joints	Left and right feet, ankles, knees, hands, wrists, elbows, hand tips, and thumbs	(3)
Angle	Neck, spine shoulder, and spine middleb	(4)
	Knee, and elbowc a
YZ-plane angle	Neck, spine shoulder, and spine middleb	(5)
	Knee, and elbowc a

^a corresponds to the mean of left and right joint measures, where the measure for each side was computed using the indicated equation.

^b considering the head, neck, and spine shoulder joints, the neck, spine shoulder, and spine middle joints, and the spine shoulder, spine middle, and spine base joints, respectively.

^c considering the hip, knee and ankle joints, and the wrist, elbow and shoulder joints, respectively.