APPLIED KINESIOLOGY PRACTICAL 1

Identify a sport code and determine the athlete or players’ Centre of Gravity

Definition of the center of gravity The center of gravity of a body is sometimes described as its balance point or that point about which a body would balance without a tendency to rotate. The center of gravity is often identified as the point where all of the weight of the body or object is concentrated. It is the point where the weight of the body is said to act. Two conditions must be met: All the linear acting on the body must be balanced. All the rotary forces must be balanced.

Placement of center of gravity in humans The location of the center of the gravity of a human being in the normal standing position varies with body build, age and sex. The center of gravity of a women is found to be 55% of their standing height and in men 56.18%. They found no correlation between the height of the center of gravity and body weight or height.

Stability and equilibrium Stable equilibrium occurs when an object is placed in such a fashion that an effort to disturb it would require its center of gravity to be raised. Unstable equilibrium exists when it takes only a slight push to destroy it. Neutral equilibrium exists when an object’s center of gravity is neither raised nor lowered when it is disturbed.

Factors affecting stability Size and shape of the base of support The size of the base of support is a primary factor in the stability of an object. Height of the center of gravity The center of gravity in a adult is located at the level of the upper third of the sacrum, but only during a normal standing position. Lowering the center of gravity will increase the stability in the body because it allows greater angular displacement of the center of gravity within the bounds of the base of support. Relation of the line of gravity of the base of support An object retains its equilibrium only so long as its line of gravity falls within its base of support. Mass of the Body The mass or weight of an object is a factor in equilibrium only when motion or an external force is involved. The greater the mass, the greater the stability. It is a matter of common observation that empty cardboard carton is more likely to blow down the street that one filled with canned goods. Friction Friction as a factor in stability has already been suggested in relation to the size of the base of support. Inadequate friction is what makes it difficult to keep one’s equilibrium when walking on icy pavement, particularly if a frisky dog tugs unexpectedly on its leash. Visual and psychological factors Factors that belong in this category are less easily explained than the others but are familiar to everyone. Physiological factors Colds and viruses and other problems that affect the inner ear may also interfere with balance.

Principles of stability Principle 1 Other things being equal, the lower the center of gravity, the greater will be the body’s stability. Ex. When landing from a jump one usually flexes at he knees, both to absorb force and to lower the center of gravity in order to regain one’s balance. Principle 1 Other things being equal, the lower the center of gravity, the greater will be the body’s stability. Ex. When landing from a jump one usually flexes at he knees, both to absorb force and to lower the center of gravity in order to regain one’s balance. Principle 1 Other things being equal, the lower the center of gravity, the greater will be the body’s stability. Ex. When landing from a jump one usually flexes at he knees, both to absorb force and to lower the center of gravity in order to regain one’s balance. Principle 1 Other things being equal, the lower the center of gravity, the greater will be the body’s stability. Ex. When landing from a jump one usually flexes at he knees, both to absorb force and to lower the center of gravity in order to regain one’s balance.

Principle 2 Greater stability is obtained if the base of support is widened in the direction of the line of force. Ex. This helps an individual to keep from being thrown off balance when punching with force, pushing a heavy object, or throwing a fast ball.

Principle 3 For maximum stability the line of gravity should intersect the base of support at a point that will allow the greatest range of movement within the area of the base in the direction of the force causing motion. Ex. A football player knowing he will be pushed from in front should lean forward so that he can “give” in a backward direction without losing balance.

Principle 4 Other things being equal, the greater the mass of the body, the greater will be its stability. Ex. In sports which resistance to impact is a factor, heavy, solid individuals are more likely to maintain their equilibrium than lighter ones. This provides one basis for selecting linemen in football.

Principle 4 Other things being equal, the most stable position of a vertical segmented body (such as a column of blocks or the erect human body) is one in which the center of gravity of each weight-bearing segment lies in a vertical line centered over the base of support or in which deviations in one direction produce torques that must be balanced by deviations production torque in the opposite direction.

Finding the center of gravity The location of the centre of gravity in human beings is of interest to scientists in many areas. Anatomists, kinesiologists, orthopedists, physical therapists, space engineers, and equipment design engineers have all shown interest in methods of determining the location of the centre of gravity.