Diagram of plane P₃ with the main parameters to calculate rotational efficiency.

<p>Two elbow positions (180° and 40°) are represented. is the projection of the pronator teres force on plane P₃. is the radial component of . is the component of tangential to the rotational movement. Angle β is the angle between and . Point A is the radial attachment site of pronator teres. Point O′ is the center of the rotational movement. Point B′ is the projection of point B on plane P₃. The position of this point varies as a function of the carrying angle of the elbow (Δ (λ), see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090319#pone.0090319.s001" target="_blank">Fig. S1</a>) and it is assessed with regards to the horizontal axis by angle. The displacement of point B′ from the horizontal axis can be calculated from the variation of point B position as a function of the elbow angle (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090319#pone-0090319-g002" target="_blank">Fig. 2</a>).