How is left trunk rotation correctly paired with its sign convention?

Left trunk rotation is correctly paired with the sign convention of +θY because this convention is often based on a right-handed coordinate system used in biomechanics. In such a system, movements that occur in the positive direction are represented with a positive sign.

When looking at trunk rotation specifically, moving to the left results in a counterclockwise motion when viewed from above. According to the right-hand rule, when the left side of the body moves forward relative to the right side during this rotation, it's classified as a positive rotation about the Y-axis. This convention helps standardize the interpretation and documentation of movements in clinical biomechanics.

In contrast, trunk flexion and extension typically relate to the X-axis, where flexion would generally be considered negative and extension positive. Similarly, right lateral flexion would occupy a different position within this three-dimensional framework, resulting in negative sign conventions. Understanding how these movements are categorized helps in accurately analyzing and describing human motion and its implications for clinical assessment and treatment.