Nightshift is associated with impaired cognitive performance on many tasks, yet performance is also moderated by individual differences. We investigated the effect of circadian type (two factors: flexible-rigid, and languid-vigour), and the efficacy of a novel countermeasure, breaking up sitting with light-intensity physical activity, in the context of nightshift performance. Thirty-three healthy adults (age M ± SD: 24.3 ± 4.6 y
19 females) participated in a sleep laboratory study over five consecutive simulated nightshifts (2200-0600 h). Sleep opportunities occurred at 0800-1700 h. Participants were randomised to a sedentary (SIT