What is the joint contact force $($mostly bone$-$on$-$bone$)$ acting at the hip?

What is the primary limitation of the static analysis of a dynamic task, that remains a

limitation even if multiple points in time are considered?

Clarification of angles for problem #$2$

Setting axes vertical and horizontal:

$a=30,$ given in problem as angle of upper body to horizontal

$c=10$ given in problem as angle of muscle insertion

$b=180($sum of internal angles$)-90-a=60$ as determined above

$d=90-60-10=20$

Setting axes parallel and perpendicular to segment:

$a=30,$ given $in$ problem $as$ angle $of$ upper body $to$ horizontal

$b=180($ sum $of$ internal angles $)-90-a=60$

$c=90-b=30$

$d=180-90-30=60$You have been called to consult at the workplace and observe this $(580$ N$)$ subject

performing a repeated lift$/$lower activity with $400$ N boxes of paper. At about $30$ o from

the horizontal position, this person complains of pain in his back while lifting the load.

You capture a $$snapshot$$ at this position to try to determine the force and torque from

the back extensors

a$.$ an angle of insertion of the muscles of $10$o

$,$

in this position. Given:

b$.$ a point of muscle insertion $5$ cm proximal to the hip joint,

c$.$ the distance from the hip joint to the line for action of the box is $40$ cm$,$

com

Fm

$2$

d$.$ the center of mass of the upper body segment is $25$ cm from the hip joint axis,

calculate the net muscle moment in a static analysis $($see figure$).$ The upper body weight

is $\mathrm{.}678$ of total body weight