C08 Physiological and cognitive responses to load carriage in the cold

Abstract

Load carriage is a vital role related task for military, emergency service, and search and rescue personnel, through the transport of critical equipment. From an external validity perspective, a common oversight in previous research is the effect of multiple stressors during load carriage; for example, the inclusion of adverse environmental conditions and/or concurrent cognitive tasks. Therefore, this study aimed to quantify physiological and cognitive changes over time during military specific fast-paced lower-weight load carriage in a cold environment. With approval from the University of Chichester’s Ethics Committee, nine participants completed a load carriage task consisting of 20 min walking at 5.1 km∙h^-1, 40 min walking at 6.5 km∙h^-1, followed by 8 × 9 s shuttles running at 11 km∙h^-1 in an environmental temperature of −10°C. Participants wore overalls whilst carrying 16 kg of external load (10 kg belt-webbing, 6 kg body armour). Throughout, measurements were taken of heart rate, core and skin temperatures, expired gas (VO₂), and ratings of physical exertion and thermal comfort. Six military-specific auditory n-back tasks (MSANT) were completed across the trial. The rating scale of mental effort (RSME) quantified mental exertion during the load carriage task. Statistical differences within variables were evaluated using a one-way repeated measures ANOVA with post-hoc analysis employed to identify differences between timepoints. Heart rate and VO₂ behaved as expected, with increases after the 5.1 to 6.5 km∙h^-1 speed escalation (P_bonf< 0.001); heart rate also increased during the shuttles compared to the first 6.5 km∙h^-1 collection (P_bonf = 0.003). A main effect rise for core temperature was evident (P_bonf < 0.001), increasing after 25 min at 6.5 km∙h^-1 (P_bonf = 0.009). Skin temperature presented a main effect (P_bonf < 0.001) with an initial decrease and plateau occurring after 15 min. There was no main effect for MSANT or RSME at MSANT completion timepoints (P’s= 0.935 and 0.368 respectively). However, during non-MSANT completion timepoints, RSME was greater from 25 min onwards compared to 5 min (P_bonf < 0.05) signifying an increase in inter-task cognitive demand, oppose to a period of relative mental recovery. This reduced efficiency could be exacerbated during concurrent or extended physical and cognitive tasks. This study is the first to examine physiological and cognitive responses to fast-paced lower-weight load carriage in the cold, progressing understanding of occupational performance in representative environments. These performance data can inform training protocols and operation approaches by highlighting higher inter-task cognitive demand, potentially emphasising an avenue for mitigation strategies.