Cognitive, Psychophysiological, and Perceptual Responses to a Repeated Military-Specific Load Carriage Treadmill Simulation

Abstract

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-min bouts of a Fast Load Carriage Protocol (FLCP), each interspersed with a 65-min 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 < .001, Kendall’s W = 69.084) and for time on the accuracy-speed trade-off parameter of the SDST ( p = .025, Ѡ2 = .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 < .001, Ѡ2 = .045; time: p < .001, Ѡ2 = .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.