Physical activity might be a nonphotic strategy which could improve cognitive performance for nightshift workers. Innate characteristics like circadian type may also influence individual performance. Thus, this study explores the relationship between circadian type and physical activity on cognition over consecutive nightshifts.
Thirty-two healthy adults (age M±SD: 24.3±4.6 years; 19 females) participated in a 7-day laboratory study, with 5 nightshifts (2200-0600). Participants were randomised into the Breaking up sitting (BUS; n=19) or Sedentary (SED; n=13) condition. Overnight, BUS participants completed 3-min bouts of light-intensity walking every 30-min, while SED participants remained seated. At 2200, 0000, 0200, 0400 and 0600, participants completed the 10-min Psychomotor Vigilance Task (mean RRT). Participants completed the 11-item revised Circadian Type Inventory (factor 1: rigid/flexible; factor 2: languid/vigorous), resulting in four-subgroups (rigid; n= 12, flexible; n= 11, and languid; n= 11, vigorous; n= 13). Participants may only be one type from either factor (i.e. rigid and vigorous).
Linear mixed models showed a significant 3-way interaction between nightshift (1-5), condition (BUS, SED), and circadian type (rigid/flexible) for mean RRT (p=0.03), such that flexible types in the Breaking up sitting condition outperformed Sedentary flexible types and Breaking up sitting rigid types, with performance worse on the first nightshift. There were no significant interactions between nightshift, condition and circadian type (languid/vigorous).