The sit-up test is used to help determine if torticollis has a muscular or ocular cause. You first observe the infants resting head position in supine and then assist the infant into a sitting position and observe the direction of the head tilt between the positions. A negative test (no ocular concern) is if the head tilt stays the same in a supine and sitting position. This suggests the head position is being driven by a muscular cause and not visual alignment. A positive test occurs when the direction of the head tilt changes when the infant is moved from supine to sitting. This suggests the head position is compensatory for visual alignment and not muscular tightness, or when in supine, gravitational demands and visual tracking demands change. If the infant’s head tilt is driven by eye alignment, the infant may reposition the head differently when visual fixation becomes more relevant (upright seated posture). In more technical terms, the head tilt is used to optimize binocular vision and reduce diplopia so when posture changes, visual demands change and head position may shift.
Rubin SE, Wagner RS. Ocular torticollis. Surv Ophthalmol. 1986;30(6):366-376. doi:10.1016/0039-6257(86)90090-1
Caputo AR, Mickey KJ, Guo S, et al. The sit-up test: an alternate clinical test for evaluating pediatric torticollis. Pediatrics. 1992;90(4):612-615.