INTRODUCTION: For tactical reasons, the foot-borne soldiers sometimes undertake nighttime operations. However, the metabolic demand during walking in complete darkness may be markedly increased. The purpose of this study was to investigate if metabolic demand and kinematics would change while walking on a gravel road and a slightly hilly trail in darkness with or without visual aid.

MATERIALS AND METHODS: Fourteen cadets (11 men and 3 women, age: 25 ± 7 years, height: 178 ± 8 cm, and weight: 78 ± 13 kg) walked at 4 km/h on a straight gravel road and on a slightly hilly forest trail (n = 9). Both trials were performed at nighttime under four different conditions, wearing a headlamp (Light), blindfold (Dark), monocular (Mono), or binocular (Bino) night vision goggles. During the 10-minute walks, oxygen uptake, heart rate, and kinematic data were assessed. Ratings of perceived exertion, discomfort, and mental stress were evaluated after each condition using a category ratio scale. Physiologic and kinematic variables were evaluated using repeated-measures analysis of variance, whereas ratings were evaluated using non-parametric Friedman analysis of variance.

RESULTS: Oxygen uptake was higher in all three conditions with no or limited vision (Dark, Mono, and Bino) than in the Light condition (P ≤ 0.02) when walking on both the gravel road (+5-8%) and the forest trail (+6-14%). Heart rate was higher during the Dark than during the Light condition when walking on the forest trail, whereas there was no difference between conditions on the gravel road. During both trials, gait frequency was higher during the Dark than during the Light, Mono, and Bino conditions. Ratings were generally low during all conditions.

CONCLUSIONS: Walking on a gravel road or a forest trail wearing a blindfold or visual aid increased the metabolic demand. Thus, it appears that the metabolic demand is higher during overground walking with night vision goggles than with full vision, which may influence the performance of nighttime operations.