Lesson
Angular Kinetics - Human Body Moment of Inertia
MOMENT of INERTIA of any object can ONLY be defined WITH RESPECT TO a
PARTICULAR AXIS of ROTATION
The AXIS of ROTATION for a human body segment making a SAGITTAL or
FRONTAL plane motion is the axis passing through the center of that segment’s
proximal joint.
[Eg. forearm flexion has an axis of rotation (mediolateral) passing
through the elbow joint-center, thigh abduction has an axis (anteroposterior) passing
through the hip joint-center.]
The AXIS of ROTATION for TRANSVERSE PLANE motion requires a segment to
rotate around its own longitudinal axis, with VERY DIFFERENT MoI. The RADIUS
Of GYRATION is much smaller in this case, and thus, so is the MoI.
PRINCIPAL AXES: Three mutually perpendicular axes passing through the TOTAL
BODY CENTER of GRAVITY
PRINCIPAL MOMENT OF INERTIA: TOTAL BODY MOI relative to one of the PRINCIPAL AXES