Left lateral flexion of the trunk is movement around the Z axis in:

Left lateral flexion of the trunk involves bending the torso to the left side. This type of movement occurs in the frontal plane, which corresponds to rotation about the Z axis. In the context of rotations, the direction of the movement determines whether it is classified as positive or negative angles of rotation.

When considering movement around the Z axis, if you visualize the three-dimensional coordinate system where the Z axis runs vertically, flexion to the left would be described as a negative angle of rotation (−θZ). This is based on the common convention in biomechanics where counterclockwise rotation is considered positive and clockwise rotation is considered negative.

Thus, the correct answer reflects that left lateral flexion of the trunk rotates towards the left side, which falls into the negative direction on the Z axis.