S TABILITY AND B ALANCE
C ENTER OF G RAVITY OR MASS The point at which the entire mass or weight of the body may be considered to be concentrated.
C ENTER OF G RAVITY OR M ASS The point around which the body’s mass is equally distributed in all directions The place where torques acting on the system are balanced The place where all the linear forces are balanced
L OCATING C ENTER OF G RAVITY IN H UMANS The human body is not rigid, so, the location of the COG depends on the location of the limbs. Intersection of three planes locates COG. The location is about 55-57% of your standing height.
STABILITY The ability of an object to return to equilibrium or to its original position after being displaced.
F ACTORS AFFECTING STABILITY Base of Support: Described by those parts of the body in contact with supporting surfaces and the intervening area. Height of the center of gravity above the base of support. Weight of the object The relationship between the BOS and the Line of Gravity.
W HAT C AUSES INSTABILITY ? External Torques: Gravity, Inertia & External Forces
W HAT C AUSES STABILITY ? Internal Torques: muscle forces, ligament forces, distribution of mass and external forces
P ROVIDING INFORMATION FOR I NTERNAL S TABILITY Vision, Somatosensory and Vestibular
S OMATOSENSORY Muscle Spindles Joint Receptors Tendon Organs Mechanoreceptors
V ESTIBULAR : THE INNER EAR Provides Information About: Head Linear Acceleration Head Rotation (angular accelerations) Head Position Meneres Disease Dizziness
W EIRD S CIENCE : T RIPPING G RANNIES
M ECHANISM OF M AINTAINING B ALANCE Activate supporting musculature Activate synergistic muscles (the core)
D AY TO DAY B ALANCE M ANAGEMENT : THE QUIET STANCE Postural Alignment Joint Stiffness/ Laxity Muscle Tone
T HE A NKLE M ETHOD For Minimal Instability: Rotation at the ankle (inverted pendulum)
T HE H IP M ETHOD For Greater Instability: Hip adjustment for increased translation
T HE S TEPPING M ETHOD For greatest instability Multiple segments involved causing slowest reaction time