The swaying action coming from the pianists' hip region constitutes the pivotal point for upper body movements. In this paper, we evaluate the relation between the use of vertical force and structural characteristics of technically different excerpts when pianists play with varied levels of expression. We also analyze the common patterns within the time-series of force data. Ten pianists performed three excerpts from the Romantic period in four expressive conditions. The force was measured with a Bertec force plate placed under the piano stool. The rhythmic and dynamic form, and the technical complexity of the excerpt, induce variations in force when pianists play with different levels of expression. Recurrent patterns of hip motion are found in specific regions of the score, which suggests that these pianists share similar movement strategies to communicate structural features.