Musculoskeletal injuries (MSI) in the military reduce soldier capability and impose substantial costs. Characterizing biomechanical surrogates of MSI during commonly performed military tasks (e.g., load carriage) is necessary for evaluating the effectiveness of possible interventions to reduce MSI risk. This study determined the effects of body-borne load distribution, load magnitude, and walking speed on tibiofemoral contact forces. Twenty-one Australian Army Reserve soldiers completed a treadmill walking protocol in an unloaded condition and wearing four armor types (standard-issue and three prototypes) with two load configurations (15 and 30 kg) for a total of 8 armor x load ensembles. In each ensemble, participants completed a 5-minute warm-up, and then walked for 10 minutes at both moderate (1.53 m⋅s^-1) and fast (1.81 m⋅s^-1) speeds. During treadmill walking, three-dimensional kinematics, ground reaction forces, and muscle activity from nine lower-limb muscles were collected in the final minute of each speed. These data were used as inputs into a neuromusculoskeletal model, which estimated medial, lateral and total tibiofemoral contact forces. Repeated measures analyses of variance revealed no differences for any variables between armor types, but peak medial compartment contact forces increased when progressing from moderate to fast walking and with increased load (p<0.001). Acute exposure to load carriage increased estimated tibiofemoral contact forces 10.1 and 19.9% with 15 and 30kg of carried load, respectively, compared to unloaded walking. These results suggest that soldiers carrying loads in excess of 15 kg for prolonged periods could be at greater risk of knee MSI than those with less exposure.

Soldiers regularly transport loads weighing >20 kg at slow speeds for long durations. These tasks elicit high energetic costs through increased positive work generated by knee and ankle muscles, which may increase risk of muscular fatigue and decrease combat readiness. This study aimed to determine how modifying where load is borne changes lower-limb joint mechanical work production, and if load magnitude and/or walking speed also affect work production. Twenty Australian soldiers participated, donning a total of 12 body armor variations: six different body armor systems (one standard-issue, two commercially available [cARM1-2], and three prototypes [pARM1-3]), each worn with two different load magnitudes (15 and 30 kg). For each armor variation, participants completed treadmill walking at two speeds (1.51 and 1.83 m/s). Three-dimensional motion capture and force plate data were acquired and used to estimate joint angles and moments from inverse kinematics and dynamics, respectively. Subsequently, hip, knee, and ankle joint work and power were computed and compared between armor types and walking speeds. Positive joint work over the stance phase significantly increased with walking speed and carried load, accompanied by 2.3-2.6% shifts in total positive work production from the ankle to the hip (p < 0.05). Compared to using cARM1 with 15 kg carried load, carrying 30 kg resulted in significantly greater hip contribution to total lower-limb positive work, while knee and ankle work decreased. Substantial increases in hip joint contributions to total lower-limb positive work that occur with increases in walking speed and load magnitude highlight the importance of hip musculature to load carriage walking.

Background Valgus knee braces have been reported to reduce the external knee adduction moment during walking. However, mechanistic investigations into the effects of valgus bracing on medial compartment contact forces using electromyogram-driven neuromusculoskeletal models are limited. Research question What are the immediate effects of valgus bracing on medial tibiofemoral contact forces and muscular loading of the tibiofemoral joint? Methods Sixteen (9 male) healthy adults (27.7 ± 4.4 years) performed 20 over-ground walking trials at self-selected speed both with and without an Ossür Unloader One® brace. Assessment order (i.e., with or without brace) was randomised and counterbalanced to prevent order effects. While walking, three-dimensional lower-body motion, ground reaction forces, and surface electromyograms from eight lower-limb muscles were acquired. These data were used to calibrate an electromyogram-driven neuromusculoskeletal model of muscle and tibiofemoral contact forces (N), from which muscle and external load contributions (%) to those contact forces were determined. Results Although walking with the brace resulted in no significant changes in peak tibiofemoral contact forces at the group-level, individual responses were variable and non-uniform. At the group-level, wearing the brace resulted in a 2.35% (95% CI 0.46-4.24; p = 0.02) greater relative contribution of muscle to lateral compartment contact loading (54.2 ± 11.1%) compared to not wearing the brace (51.8 ± 12.1%) (p < 0.05). Average relative contributions of muscle and external loads to medial compartment loading were comparable between brace and no brace conditions (p ≥ 0.05). Significance Wearing a valgus knee brace did not immediately reduce peak tibiofemoral contact forces in healthy adults during normal walking. It appears this population may modulate muscle activation patterns to support brace-generated valgus moments, thereby maintaining normal walking knee moments and tibiofemoral contact forces. Future investigations are warranted to better understand effects of valgus knee brace in people with medial knee osteoarthritis using an electromyogram-driven neuromusculoskeletal model.

Soldiers carry heavy loads that may cause general discomfort, shoulder pain and injury. This study assessed if new body armour designs that incorporated a hip belt reduced shoulder pressures and improved comfort. Twenty-one Australian soldiers completed treadmill walking trials wearing six different body armours with two different loads (15 and 30 kg). Contact pressures applied to the shoulders were measured using pressure pads, and qualitative assessment of comfort and usability were acquired from questionnaires administered after walking trials. Walking with hip belt compared to no hip belt armour resulted in decreased mean and maximum shoulder pressures (p < 0.005), and 30% fewer participants experiencing shoulder discomfort (p < 0.005) in best designs, although hip discomfort did increase. Laterally concentrated shoulder pressures were associated with 1.34-times greater likelihood of discomfort (p = 0.026). Results indicate body armour and backpack designs should integrate a hip belt and distribute load closer to shoulder midline to reduce load carriage discomfort and, potentially, injury risk. Practitioner Summary: Soldiers carry heavy loads that increase their risk of discomfort and injury. New body armour designs are thought to ease this burden by transferring the load to the hips. This study demonstrated that designs incorporating a hip belt reduced shoulder pressure and shoulder discomfort compared to the current armour design.

Musculoskeletal injuries are reported as burdening the military. An identified risk factor for injury is carrying heavy loads; however, soldiers are also required to wear their load as body armour. To investigate the effects of body armour on trunk and hip kinematics during military-specific manual handling tasks, 16 males completed 3 tasks while wearing each of 4 body armour conditions plus a control. Three-dimensional motion analysis captured and quantified all kinematic data. Average trunk flexion for the weightiest armour type was higher compared with control during the carry component of the ammunition box lift (p < 0.001) and sandbag lift tasks (p < 0.001). Trunk rotation ROM was lower for all armour types compared with control during the ammunition box place component (p < 0.001). The altered kinematics with body armour occurred independent of armour design. In order to optimise armour design, manufacturers need to work with end-users to explore how armour configurations interact with range of personal and situational factors in operationally relevant environments. Practitioner Summary: Musculoskeletal injuries are reported as burdening the military and may relate to body armour wear. Body armour increased trunk flexion and reduced trunk rotation during military-specific lifting and carrying tasks. The altered kinematics may contribute to injury risk, but more research is required.