A patient rotates their torso to the right. This action is best described in terms of which sign?

• A. +θX
• B. −θX
• C. +θY
• D. −θY

Answer: (D)

When a patient rotates their torso to the right, this movement can be best understood in terms of angular displacement around the vertical axis, which corresponds to the Y-axis in biomechanics terminology. This rotation is described as a negative angle, often denoted as -θY, because rotations to the right from the perspective of an anatomical position typically are assigned a negative angular value in a right-handed coordinate system.

This is based on standard conventions used in biomechanics and physics, where the counterclockwise rotation about an axis is considered positive and clockwise rotation is negative. Since the torso rotation described is to the right and resembles clockwise motion from a typical viewpoint, it takes on the negative designation to reflect this direction of movement accurately.

Understanding this convention is crucial for interpreting motion in clinical biomechanics, where precise descriptions are necessary for assessments and communication regarding patient movements and therapy strategies.