Rotating the trunk to the left occurs around the Y axis in which direction?

Rotating the trunk to the left occurs around the Y axis in a positive direction, which is why the answer is +θY. In biomechanics, rotation around the Y axis is typically defined based on a standard coordinate system where positive rotation indicates a counterclockwise movement when viewing the body from above.

When the trunk is rotated to the left, it moves away from its starting position in a counterclockwise direction from the perspective of an observer, thereby aligning with the positive designation of that rotation. This understanding is essential in biomechanics as it helps clarify how movements are quantified and analyzed in terms of degrees and directional rotation, particularly in relation to posture and dynamic activities.

This concept also serves as a foundation for understanding more complex movements. For example, when analyzing athletic performance or rehabilitation exercises, recognizing how each segment of the body rotates can influence overall biomechanics and movement efficiency.