We investigate how reading text in augmented reality (AR) glasses and the simultaneous execution of three real-world tasks interfere with each other. The three tasks are a visual stimulus-response task (VSRT), a simple walking task and a walking obstacle course. Also, we investigate the effects of different AR text positions on primary task and reading performance as well as subjective preference. We propose a novel out of sight body-locked text placement for AR text presentation to be used in dual-task situations and compare it to head-locked text placement, each in two heights. AR reading affected performance in all tasks and reading speed was affected in all dual-task conditions. Participants subjectively preferred the body-locked text presentation, while objective measures do not reflect that preference. Differences between the tasks and several interaction effects between task and AR text placement demonstrate the necessity to carefully consider the context of use when designing AR reading UIs. The presented study with 12 participants provides insights into the effects of AR glasses usage in dual-task situations and several design recommendations are derived from the results.