Cognitive workload can affect task performance in a number of ways. In occupations where workload is a constant factor, it is important that individuals are selected and trained to cope with high task demands. Literature using physiological measures to assess performance under load has suggested that individuals can enter two states when faced with increasing task demands; threat or challenge. These physiological states reflect mental subprocesses, where individuals see the task as challenging (wanting to increase performance) or threatening (anxiety inducing). The current study aims to draw links between behavioural and physiological outcomes of cognitive workload. Two studies were conducted; an online study – where participants completed a tracking task and simultaneous behavioural workload measure as well as a pre and post experiment questionnaire; and an in lab study – where participants completed two workload inducing tasks (the Cedar Operator Workload Assessment Tool and a collision detection task) over two sessions. During these sessions, participants were equipped with physiological measurement tools and completed a behavioural workload measure. Results so far have shown that the workload measure captured changes in task difficulty and was related to subjective cognitive workload. Physiological measures also found differences between task difficulty conditions. Participants mental state could be inferred from the physiological measurement. Results so far are promising, with physiological measures successfully differentiating between individuals state of arousal and the workload measures differentiating between levels of cognitive workload as difficulty changed. Going forward, we aim to show a measure of workload and state over time, to observe the effects of state on performance and experienced workload, and further develop a unified measure of task performance. This research has implications and applications for further work with assessment and training of air traffic controllers.