openstaxorg 9.6 Forces and Torques in Muscles and Joints QAA Triceps Free-body muscle diagram . Biceps * muscle /\\/ Fe ma 2 2.5 kg wail wb co FE we 38 cm CG Wb CG a l"1 r2 '33 (b) Figure 9.26 (a) The figure shows the forearm of a person holding a book. The biceps exert a force F3 to support the weight of the forearm and the book. The triceps are assumed to be relaxed. (b) Here, you can View an approximately equivalent mechanical system with the pivot at the elbow joint as seen in Example 9.4. EXAMPLE 9.4