Fig. 1.

Model of forelimb mechanics during quadrupedal suspension in various elbow joint angles from (A) flexed to (D) extended. The elbow is subject to an extensor torque induced by body weight and resisted by counteracting muscle forces times moment arms (M_n). M₂ and M₁ are maximized at the specific elbow joint angle shown in (B) and (C), where the lines E-Lsc and E-Rt are perpendicular to Fl₂ and Fl₁, respectively. E, centre of elbow joint rotation; Fl₁ and Fl₂, flexor muscle groups along the brachium and antebrachium, respectively; M₁ and M₂, moment arms of Fl₁ and Fl₂, respectively; Lsc, lateral supracondylar crest; Rt, radial tuberosity; S and W, shoulder and wrist joints, respectively.