Set up a free body diagram of the elbow and use it to derive an equation solving for the biceps brachii muscle force when performing an isometric bicep exercise with a 20 kg weight. Solve for the biceps force (FB) in terms of the following variables (do not plug in numbers at this point). Assume the humerus is kept vertical and the elbow is flexed 60° (remember straight arm is 0° of elbow flexion). Remember to draw your FBD large enough to have room to work (i. e. use a whole sheet of paper!).

Fb = Biceps brachii muscle force

MA = Biceps moment arm

Theta = Elbow flexion angle

L = Distance from the elbow COR to center of mass of forearm

m = Forearm mass X Distance from the elbow COR to the point of application of the external load

Fr = Resistive force of the weight during isometric flexion exercise

g Gravitational constant

Your FBD should show 3 forces: the force from the external resistance (Fr), the force due to weight of the forearm (mg), and the force due to the biceps brachii muscle (Fb).