Kinesiology 3rd Sec PDF

COG DEFINTION:  It is an imaginary balancing point where the body weight assumed to be concentrated.  it is the balancing point for an object or subject.  The center around which the body may rotate freely in all directions.  The summation of all forces at this point equal zero  The...

COG DEFINTION:  It is an imaginary balancing point where the body weight assumed to be concentrated.  it is the balancing point for an object or subject.  The center around which the body may rotate freely in all directions.  The summation of all forces at this point equal zero  The summation of all moments at this point equal zero Determination of COG location 1-Mathematical method Mathematical method Croskey Palmar formula formula (without (regarding to regarding to sex) sex)  (A)Croskey formula (regarding to sex) Height of female COG measured from heel : Total body height ×55.4 100 Height of male COG measured from heel: Total body height×56.18 100 (B)Palmar formula (without regarding to sex) Total body height ×55.7 +1.4 100 Male subject of 170cm form by palmar formula = 170 × 55.7/100 +1.4= 96.09 cm by crokskey formula = 170 ×56.18/ 100 = 95.5cm  Determination segmental body COG Body segments consists of :14 OR 16 segments To determine the segmental COG of any segment: (A)(if segment in straight position) : 1- measure the segmental length of this segment 2- find mathematically the of segmental COG by multiplying the segmental by 4/7, then the final product is then measured from the distal end. Combined segment COG - If segments are straight position Segment Proximal end Distal end Arm Acromion process Axis of elbow Forearm Axis of elbow Axis of hand Hand Axis of hand Tip of fingers Thigh Greater trochanter Axis of knee Leg Axis of knee Lateral malleolus Foot Heel Tip toes Head & neck Sternal notch Top of the head Trunk Sternal notch Midline between 2 hips Combined segment COG - If segment not on straight position: If the body move in flexion as in upper and lower limb , the COG of the entire part can be computed from the COG of each segment. When a limb is flexed , the single center may be found outside the limb. Value of determination of COG : 1- Total COG 1)Decide best sites to give stabilization to patients e.g. hemiplegic patients 2)It will help the bio-mechanist to improve the player’ performance.  2- segmental COG 1- In amputation. The distribution of the wt. of Artificial limb must be equivalent to that of the amputated limb Stability Definition : Is the ability to maintain one’s balanced in both static and dynamic situation without use of mechanical devices. Factor affecting stability :  Center of gravity  Base of support  Relation between line of gravity and BOS  Characteristic of the supporting surface  Segmentation principle  subject’s state 1- Center of gravity : The lower COG the greater will be the body‘s stability. I.e Standing is less stable than kneeling ?? As in kneeling the COG height is lower than standing standing is more stable than standing on toes. Wearing high heeled shoes decrease. one’s stability because it displace the COG upward. 2- Base of support: BOS is the supporting area under the body. It include the points of contact with the supporting surface and the area between them. These points may be body parts such as The feet or hands or they may be extension of body parts such as crutches or other walking aids. If the patient walks with sticks or crutches the BOS is the area between the crutches and feet Effect of BOS: 1- An increase in the BOS will be associated with an increase in the stability. The upright human body is least stable when the feet are parallel and close together. As the feet are moved apart , the base increased and the person becomes less likely to fall. 2- The increase in the shape of the BOS occurs in the direction of the force being applied to the body. When a force is applied from behind , the shape of the base is enlarged in the forward direction allowing greater stability. Abroad base in the direction of body movement is essential in such activities as giving assistance and support of a patient who is walking or raising from or being seated in a chair. Stability of the therapist is vital for safety as well as for the ease of movement. 3- Relation between line of gravity and BOS: line of gravity is a vertical line that pass through the COG and falls within BOS. It’s essential that the LOG should fall within BOS to mantaine balance  The nearer the LOG to the center of BOS, the greater the stability. In stride standing , LOG lies within BOS. IF the a subject stand on toes, the LOG will become near to edge of BOS , so any push to the subject will disturb standing easier than if LOG is in the middle of BOS  4- Supporting surface A- friction : The greater friction between the supporting surface and the parts of the body which are contact with it , the more stable the body will be. But this friction should be up to certain limit, after this limit the friction would act as a distributing factor. EXAMPLES: Basket ball or football players wear rubber soled shoes to increase friction between his body and the floor Patients use crutches with rubber ends to increase Friction between floor and the crutch  B- softness of the supporting surface : Hard mattress should be used to increase stability and to conserve energy of the patient C- inclination of the supporting surface : The greater the inclination the less stability. This concept are important for constructing outside ramps for wheelchairs and patient who are using crutches , if this ramp is steep a wheel chair may not be able to go up the ramp 5- Segmentation principle If there is deviation of apart of the body to certain direction , there is another compensatory deviation of another part of the body to the opposite direction to maintain balance during this position Examples: When carry heavy wt , the body shift in opposite direction in order to compensate. , If the a wt is carried in one hand ,the opposite arm is lifted to help counterbalance a very heavy load held in one hand Carry a heavy wt in front of the body lead to compensatory movement in trunk backward to move LOG with in the BOS. Any abnormal disturbance in the curvature of the spine is compensated by another deviation i.e primary C scoliosis if neglected will be compansated later by secondary curves lead to S scoliosis 6-subject state A- mass : The greater the mass of the body , the greater will be its stability. Carrying weight in both hands will increase stability than in case of carrying a wt in one hand. B- vision: a person has a greater balance and stability in locomotion when he focuses his vision on a stationary object rather than on moving or disturbance one. C- physical and emotional state: Disabled person is less stable than a healthy one. Pain decrease stability especially if the pain affect the lower extremities D- age : The person will be more stable in adulthood period than in childhood and the stability will also decrease in senile subjects due to physiological Changes occurring as a result of aging process.