The present study utilized a novel methodological combination of eye tracking and postural movement recordings to study task-induced changes in cognitive engagement during expository text reading. Thirty-three participants read an expository text with a specific task in mind while their eye and postural movements were concurrently recorded, and after reading recalled the text from memory. The results showed that readers spent longer total fixation time and had better memory for task-relevant than irrelevant text information. During the course of reading, head-to-screen distance and the speed of head motion decreased more for relevant than irrelevant text segments. The results support the dynamic engagement hypothesis: there is task-induced fluctuation in cognitive engagement during reading. Moreover, the results suggest two types of engagement processes: transient and sustained engagement. The former refers to fast, momentary changes, whereas the latter refers to slower changes in the level of engagement observed across the reading task. The novel combination of eye and postural movement recordings proved to be useful in studying how readers embody the cognitive task demands during reading.