Vertical Load Placement Does Not Alter Metabolic Responses In Females During Load Carriage

Previous work elucidating metabolic responses of load placement during ruck marches have primarily been in male subjects. Females’ responses to mass placement in a rucksack during load carriage are less understood but are required to optimize mission planning. PURPOSE: To test the hypothesis that females would have similar metabolic responses during rucksack-borne load carriage in two differing vertical close-to-the-back load placements. METHODS: In a crossover design, ten females (25 ± 4 y; 161.6 ± 6.4 cm; 67.4 ± 9.6 kg) completed two 4.8 km walks loaded with 30% of their body mass (20.2 ± 2.9 kg). The load mass was placed 14.0 cm (Center-Close) and 24.1 cm (High-Close) from the bottom of the rucksack and close to the body in a random order. Subjects were instructed to complete the walk as quickly as possible (54 ± 4 min). Expired gases were measured the minute prior to reaching 1.6, 3.2 and 4.8 km when intensity was constant (5.6 km·h-1, 2.5% grade). Oxygen uptake (V̇O2), respiratory exchange ratio (RER), and minute ventilation (V̇E) were analyzed using repeated measures ANOVA and post-hoc paired t-tests. RESULTS: V̇O2, RER, and V̇E did not differ between the load configurations at any time (see table). Over time, changes in V̇O2 were observed in the high-close condition, and changes in RER and V̇E were observed over time in both conditions (see table). CONCLUSIONS: Metabolic responses to load carriage in females were similar between a high and central position when close to the body. Over time, the high position evoked greater metabolic responses. While males generally carry rucksack-borne loads more efficiently when packed high and close, females show similar responses when the load is located close either centrally or high. However, the increased demands of the high-close position over time should be further investigated for implications on substrate utilization and energy expenditure.