The document discusses a formula used to calculate the force (F) exerted by lower back muscles when bending at the waist with a straight back. The formula treats force as a function of the angle (x) between the torso and horizontal and the person's weight (W). It provides an example calculation for a person named Sally who weighs 500N and bends at angles of 0 and 90 degrees, finding the force is 1445N and 0N respectively.

1. DID YOU KNOW THAT …
If a person having a weight W bends at the waist with
a straight back, the stress on his back through a force
F exerted by his lower back muscles may be
computed using the formula
It has been derived as a function of the angle x
between the person’s torso and the horizontal.
 o
90xsinW89.2F 

4. Why do you need to have
proper posture while sitting?
Standing? Walking?

5. Sally, who works out
regularly in a gym, weighs
500 N. In one of her sessions,
she needs to bend as much
as she can while holding a
weighted metal bar

6. Sally, who works out regularly in a gym, weighs 500N. In
one of her sessions, she needs to bend as much as she
can whholding ile a weighted metal bar
Using the formula
Where F = force exerted by the lower back muscles
W = weight of the person in newton
x = angle between Sally’s torso and the
horizontal.
 o
90xsinW89.2F 
Determine the corresponding values of F when x = 0 or x
= 90 and interpret.

7. x = 0
F = 2.89 (500) sin(0 + 90)
F = 1445 sin 90
F = 1445 (1)
F = 1445 N
x = 90
F = 2.89 (500) sin(90 + 90)
F = 1445 sin 180
F = 1445 (0)
F = 0
INTERPRET

8. TRIGONOMETRIC EQUATION
 o
90xsinW89.2F 
It is an equation that contains trigonometric
expression with a variable.