Primarily hip-borne load carriage does not alter biomechanical risk factors for overuse injuries in soldiers

Abstract

Objective: To examine the effects of different body armour types, carried loads, and walking speeds on trunk and lower-limb joint biomechanics. Design: Within-subjects repeated measures design to examine the effects of different body armour types, carried loads, and walking speeds on trunk and lower-limb joint biomechanics. Method: Twenty soldiers (29.5±7.1yrs) completed a treadmill walking protocol in an unloaded (baseline) condition and wearing a control, Tiered Body Armour System (TBAS) and five different armour types (cARM1-2, pARM1) with two load configurations (15 and 30 kg) for a total of eight armour x load ensembles. In each ensemble, participants walked for 10 minutes at 1.53 m⋅s-1 and 1.81 m⋅s-1 speeds. Whole-body marker kinematics and ground reaction forces were used, along with a scaled anatomical model, to determine peak lower-limb joint angles, net joint moments, and negative knee work. Peak parameters were compared between armour types, walking speeds and carried loads using repeated measures ANOVAs. Results: Peak plantarflexion and hip abduction moments were reduced when wearing cARM1 (p=0.040, p=0.045) and cARM2 (p=0.045, p=0.003) compared to TBAS while carrying 30kg and/or walking fast, suggesting positive benefits of load distribution at higher demands. Joint moments increased when participants carried greater load and/or walked faster, and the combined effects of carried load and walking speed were mostly additive. Conclusions: Importantly, primarily hip-borne load carriage does not negatively alter joint kinetics, and some positive adaptations occurred during tasks with higher demands. These results can inform equipment design and physical training programs for load carriage.

Gait and neuromuscular dynamics during level and uphill walking carrying military loads

“…The extent to which load may impact the mechanical and therefore neuromuscular function of walking gait is dependent on both the magnitude and distribution of the load (Birrell & Haslam, 2010; Lenton et al, 2019; Seay et al, 2014). There are a number of load carriage strategies adopted by militaries, such as traditional backpacks, weaponry held in the hands or on the trunk and webbing, a vest with load carried close to the waist (Knapik et al, 2004; Walsh & Low, 2021).…”

“…Backpack load carriage systems, which position the mass behind the trunk, require compensations in trunk, hip and knee kinematics and kinetics to prevent a loss of stability (Liew et al, 2016). Whereas, systems that position the load closer to the hips or distributed around the waist, such as webbing systems, require less compensation in joint kinetics (Lenton et al, 2019; Seay et al, 2014). This indicates lower mechanical demands and potentially different neuromuscular control adaptions to the load.…”

Role of sex and stature on the biomechanics of normal and loaded walking: implications for injury risk in the military

“…Peak hip and knee, flexor and extensor moments, and peak ankle plantar flexor moments increase with increasing load [21,46,61,70,71]. Although the relative increase in joint loading due to load carriage is likely speed dependent, the largest increase in joint moment consistently occurs at the knee joint [46,70].…”

Weighted Vest Load Arrangement and Data Normalization Effects on Lower Limb Biomechanics During Countermovement Jump Landings

“…Weighted vests are typically positioned, so the load is arranged symmetrically over the trunk or upper body [24]. Literature has reported changes in posture and gait patterns with different loading arrangements [39]- [41], showing fewer modifications in biomechanical demand when the load is closer to the hip and the body's center of mass [42], [43].…”