An object in static equilibrium it is not moving. Therefore by definition no work is done.
This is sometimes hard to imagine if you are holding a jug of milk out at arms length, but remember, 

Work = Force*Distance.

Physiologists used to find this hard to comprehend, so in 1864 the physiologist Hendenhain coined the term,
"static work." He was able to rationalize this oxymoronic term because even if there is no external work being done, there is internal work being done within the muscle fibers.  Cross bridges are formed and the protein filaments actin and myosin slide past each other to compensate for the certain amount of stretch in the muscle's tendon.

Holding an object steady at arms length does no mechanical work, but it does use energy and contribute to muscle fatigue.



http://www.balleteast.org/images/Angie%20and%20Jeremy(lift).jpg

In an isometric contraction, the lever system of muscle and bone
is in static equilibrium. That is, the sum of the forces and torques
equal zero.

              X:  ΣF=0      Y:  ΣF=0       Στ =0 =


Using these equations and a free body diagram, the forces in the joint and the muscular tension can be found.

 Στ =0 = xT-dmg    => T = dmg/x
                                    T = 0.35m*50N/0.053m
                                    T =  500N
X:  ΣF=0                                                                                                                                          Image Edited by Kelsey     
Y:  ΣF=0 = T-Jy-mg   => Jy = T-mg
                                        Jy = 500N-50N
                                        Jy = 450N