An Exploratory Analysis of The Role of Sex in Load Carriage

Author

• Rachel E. Perez, The University Of MontanaFollow
• Dustin R. Slivka, The University Of MontanaFollow
• Brent C. Ruby, The University Of MontanaFollow

Year of Award

2026

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Integrative Physiology (Exercise Science option)

Department or School/College

Integrative Physiology and Athletic Training

Committee Chair

Dr. Dustin Slivka

Commitee Members

Dr. Brent Ruby, Dr. Brian Loyd

Keywords

Body composition, Metabolic cost, Aerobic capacity, Dead mass, Fat mass, Pack load

Subject Categories

Exercise Physiology | Exercise Science | Expeditionary Education | Integrative Biology | Sports Sciences | Systems and Integrative Physiology

Abstract

Axially loaded weight may impose a metabolic demand equivalent to that of fat mass (FM) during load carriage. Males (M) typically have a lower body fat percentage than females (F), resulting in metabolic demand differences during load carriage that may be mitigated by accounting for FM in pack loads. PURPOSE: To determine whether normalizing pack load to FM equalizes metabolic cost across sexes during load carriage. METHODS: Twenty-eight participants (14M, 23 ± 5 y, 1.81 ± 0.07 m, 78.7 ± 10.0 kg, 12.7 ± 5.4% body fat, VO₂peak 4.18 ± 0.54 L·min^-1; 14F, 22 ± 4 y, 1.68 ± 0.07 m, 63.7 ± 8.1 kg, 22.6 ± 5.2% body fat, VO₂peak 2.76 ± 0.47 L·min^-1) were recruited. The preliminary visit included measures of height, weight, body composition, and treadmill VO₂peak. The experimental visit consisted of 2 trials of treadmill walking at 1.34 m·s^-1 and 10% grade for 10 minutes while measuring expired gases, heart rate, and rating of perceived exertion. Trials were separated by 15 minutes of rest. Load order was randomized between pack weights of 30% of body mass (30%BM) and 30% of body mass minus absolute FM (SubFM). RESULTS: There were no sex differences in VO₂ during 30%BM loading (M 31.4 ± 2.0, F 31.6 ± 1.4 mL·kg^-1·min^-1, p = 0.772), but M were greater than F during SubFM loading (M 27.8 ± 2.0, F 25.6 ± 2.2 mL·kg^-1·min^-1, p = 0.010). Percentage of VO₂peak was lower in M (30%BM 60 ± 9%, SubFM 53 ± 7%) than F (30%BM 74 ± 6%, SubFM 60 ± 6%, p < 0.001) across load conditions. The magnitude of F elevation in percentage of VO₂peak over M was 13.9% in the 30%BM condition (p < 0.001) and 7.0% in the SubFM condition (p = 0.010). CONCLUSIONS: FM-adjusted pack loads reduce, though don’t completely normalize sex differences in the metabolic cost of load carriage. Relative VO₂ (mL·kg^-1·min^-1) was standardized during 30%BM loading, whereas SubFM better adjusted the percentage of VO₂peak. Load prescription methods should therefore be selected based on the desired type of sex normalization.

Recommended Citation

Perez, Rachel E.; Slivka, Dustin R.; and Ruby, Brent C., "An Exploratory Analysis of The Role of Sex in Load Carriage" (2026). Graduate Student Theses, Dissertations, & Professional Papers. 12644.
https://scholarworks.umt.edu/etd/12644