Which type of labor mechanism does NOT include contraction?

The vertex position is characterized by the baby's head presenting first during labor, which is the most common and optimal presentation for a successful vaginal delivery. In this scenario, the term "contraction" is misleading because the mechanism of labor primarily focuses on how the baby navigates the birth canal. While contractions are involved in the process of labor regardless of the position, the question emphasizes the type of mechanism that doesn't directly relate to contractions used during labor stages.

In contrast, breech and transverse positions indicate that the baby is not head-down, which can complicate or alter the standard mechanisms of labor, but that does not inherently eliminate the role of contractions. Normal vaginal delivery also necessitates contractions to expel the baby when in a vertex position. Thus, although contractions are present in all labor mechanisms, the vertex position stands out as initially being less directly associated with the force of contractions making it the focus of this question.