Background: Dismounted military operations require soldiers to complete cognitive tasks whilst undertaking demanding and repeated physical taskings.
Objective: To assess the effects of repeated fast load carriage bouts on cognitive performance, perceptual responses, and psychophysiological markers.
Methods: Twelve civilian males (age, 28 ± 8 y; stature, 186 ± 6 cm; body mass 84.3 ± 11.1 kg; V̇O2max, 51.5 ± 6.4 mL·kg-1·min-1) completed three ~65-minute bouts of a Fast Load Carriage Protocol (FLCP), each interspersed with a 65-minute recovery period, carrying a representative combat load of 25 kg. During each FLCP, cognitive function was assessed using a Shoot-/Don’t-Shoot Task (SDST) and a Military-Specific Auditory N-Back Task (MSANT), along with subjective ratings. Additional psychophysiological markers (heart rate variability, salivary cortisol, and dehydroepiandrosterone-sulfate concentrations) were also measured.
Results: A main effect of bout on MSANT combined score metric (p<0.001, Kendall’s W=69.084) and for time on the accuracy-speed trade-off parameter of the SDST (p=0.025, Ѡ2=0.024) was evident. These likely changes in cognitive performance were coupled with subjective data indicating that participants perceived that they increased their mental effort to maintain cognitive performance (bout: p<0.001, Ѡ2=0.045; time: p<0.001, Ѡ2=0.232). Changes in HRV and salivary markers were also evident, likely tracking increased stress.
Conclusion: Despite the increase in physiological and psychological stress, cognitive performance was largely maintained; purportedly a result of increased mental effort.
Application: Given the likely increase in dual-task interference in the field environment compared with the laboratory, military commanders should seek approaches to manage cognitive load where possible, to maintain soldier performance.