Human Factors professionals regard Multiple Resource Theory (MRT) as a plausible explanation of the human cognitive processing system, but the theory lacks extensive testing with physical tasks. This is potentially a problem, because dual-tasking with cognitive and physically demanding tasks is a common requirement in high-risk settings such as military operations, firefighting, and search and rescue operations. Previous researchers utilized a verbal free recall task, a task demanding verbal processing resources, paired with a climbing task and reported dual-task interference. In the present work, the verbal free recall task was paired with a semantic discrimination task, a running task, and a spatial puzzle task. By holding one task constant amongst a variety of dual-task pairs, it becomes more feasible to analyze not only how much interference is occurring, but also why. The remaining five experiments pursued the overarching theme by utilizing a new verbal situation awareness (SA) task in place of the verbal free recall task. The SA task placed greater demands on episodic or narrative verbal memory more similar to real-world situations. The SA task was paired with the secondary tasks above, as well as a climbing task and a response inhibition task. It was found that the specific resources required, as well as the executive resource requirement (e.g. manipulation, planning) of a task both contribute to the dual-task interference. Climbing required resources beyond the scope and nature of what would be expected according to the MRT; the total dual-task inference for this task exceeded the interference for the other task pairs. In order to better avoid dangerous dual-tasking situations and to provide appropriate aid if those situations cannot be avoided, assessing both the specific and general resource demands of any physically and cognitively challenging task that might be required in high-risk operations is critical.