Abstract
BACKGROUND: Military personnel in combat roles observe a high prevalence of knee osteoarthritis. Knee total joint moment (KTJM) and the knee adduction moment percentage contribution (KAM%) of KTJM have been linked to knee osteoarthritis. It is postulated that sex, load carriage, and imposed locomotion patterns such as forced marching (FM) alter mechanics of the knee. The purpose of this study was to determine the effects of "military-relevant" load magnitudes, locomotion patterns, and sex on KTJM and its planar percentage contributions in recruit-aged adults during short-duration gait tasks. HYPOTHESIS: The greatest load magnitude and FM will significantly increase KAM contribution to KTJM compared with lower magnitudes or no load. Additionally, women will exhibit greater KAM contribution to KTJM compared with men regardless of experimental condition. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty healthy recruit-aged (18-35 years) adults (10 male, 10 female) executed trials of running and FM with no load (BW), an additional load of 45% of BW, and an additional load of 55% of BW. KTJM was calculated along with each plane of motion percentage contribution: knee flexion moment (KFM%), KAM%, and knee rotation moment (KRM%). A 3 × 2 × 2 mixed model analysis of variance was used to evaluate the effects of load carriage, locomotion pattern, and sex on KTJM, KFM%, KAM%, and KRM% at multiple gait events of stance phase. RESULTS: FM exhibited a greater (P < .001) KTJM than running at heel strike. Running had greater KAM% (P = .01) and KRM% (P < .001) compared with FM. At midstance, running exhibited greater (P < .001) KTJM than FM for each load condition; however, FM had greater KAM% (P < .001) and KRM% (P = .002) compared with running at peak vertical ground reaction force and midstance. Men exhibited greater KAM% at heel strike (P = .02) independent of locomotion pattern and at midstance (P = .04) for FM. CONCLUSION: Load carriage increases KAM% to a magnitude similarly observed in populations with knee osteoarthritis, especially when executing FM. Interestingly, men exhibited greater KAM% than women, suggesting differing strategies to motor execution with relative load carriage. CLINICAL RELEVANCE: Screening recruits for greater KAM% during loaded gait tasks may identify individuals in need of specialized training to reduce the risk of knee osteoarthritis development.