OBJECTIVE: To illustrate a CG location technique in a static body position.

DIRECTIONS: Place the reaction board on the scales and adjust the scales to eliminate the weight of the board. The subject lies on the board with his head in line with the metal support attached to the bottom of the board. Read the scales. Record the weight from Scale 1, which is the scale nearest the head of the subject. Record the weight from Scale two, which is nearest the feet of the subject.

Weight 1 = w₁ = _____________

Weight 2 = w₂ = _____________

d₁ = will represent the unknown distance from the top of the head of the Subject to the CG

d₂ = represents the distance from the feet of the subject and will be found as follows:
d₂ = (72.5" - d₁) the total distance between the board supports is 72.5"

Solve the following equation:

w₁ * d₁ = w₂ * d₂

w₁ * d₁ = w₂ (72.5" - d₁)

(w₁ * d₁) = 72.5w_{2 -} - (w_{2 *} d₁)

(w₁ * d₁) + (w_{2 *} d₁) = 72.5"* w₂

(w₁ + w₂) d₁ = 72.5"*w₂

d₁ = 72.5 " * w₂

(w₁ + w₂)

Measure from the top of the head the distance you calculated for d₁ and mark that spot with a safety pin.

What does this point represent?

1. What is the total height of the subject?

2. What is the height of the CG of the subject?

3. What is the percent of height of the subject’s CG?

OBJECTIVE: To locate the CG in a balanced stance.

DIRECTIONS: Attach the plumb line to the safety pin. Place the two scales 12 inched apart. Stand on the scales and distribute the weight so that both scales have the same reading.

4. What is the size of the base?

5. Where does the plumb (gravitational) line point?

6. Where is the CG with respect to the various edges of the base?

OBJECTIVE: To demonstrate the relocation of the CG laterally with a lateral weight shift.

DIRECTIONS: Shift the weight so that two-thirds of the weight registers on one scale.

7. What happened to the gravitational line?

8. In what direction and how far did the CG move on the base?

OBJECTIVE: To illustrate the relocation of the CG anteriorly and posteriorly with an A-P weight shift.

DIRECTIONS: place the scales side by side touching each other. Stand on the scales with both feet so that the balls of the feet are on one scale and the heels on the other. Attach plumb line to side of the hip.

9. What happens to the scale readings as weight is shifted from the balls of the feet to the heels and back again?

10. Comment on weight placement and shifting of the feet in any direction as they relate to location of CG.

11. Relate the direction of the plumb line to weight placement.

OBJECTIVE: To demonstrate the weight shift caused by lateral movement of the arms.

DIRECTIONS: Stand on the two scales placed side by side in contact so that each has half of the weight registered. Move both arms to the right fully extended at shoulder height.

12. What happened to the scale readings?

13. Why?

OBJECTIVE: To demonstrate the lateral influence of a vertical weight shift on CG location.

DIRECTIONS: Raise both hands straight up above the shoulders

14. What happened to the scale readings?

15. Why?

16. Compare the stability in these two situations.

OBJECTIVE: To illustrate the relationship between weight distribution and stability factors.

DIRECTIONS: Put on a backpack full of books and stand on the scales with heels on one and toes on the other.

17. Discuss the body position, gravitational line and stability as seen from the side in terms of the influence of the backpack on them.

Sources:

Adrian, M & Cooper, J. (1989). Biomechanics of Human Movement. Indianapolis,: Benchmark Press, Inc.

McCarthy, J. (1979). Biomechanics Laboratory Exercises and Workbook. 2nd Ed. Minneapolis, Minnesota: Burgess Publishing Co.