Lower-limb joint work and power are modulated during load carriage based on load configuration and walking speed

Abstract

Soldiers regularly transport loads weighing >20 kg for slow speeds over long durations. These tasks elicit high energetic costs through increasing 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 soldier participants donned a total of 12 body armor variations: six body armor systems (one standard-issue, two commercially available [cARM1-2], and three prototype [pARM1-3]) and two load magnitudes (15 and 30 kg). In 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. From these, hip, knee, and ankle joint work was 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 ankle to hip (p<0.05). Compared to using cARM1 with 15 kg of carried load, carrying 30 kg caused significantly greater hip contribution to total positive work, while knee and ankle work decreased. Substantial increases in hip joint contributions to total positive work with increases in walking speed and load magnitude highlight the importance of hip musculature to positive power generation in load carriage walking. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Military load carriage effects on the gait of military personnel: A systematic review

“…Load carriage also increased tibiofemoral joint contact forces but without altering individual muscle relative contribution to joint contact forces when wearing body armour and backpack loads (Lenton et al, 2018). Total, hip, knee and ankle sagittal power generation was also increased by load carriage with hip and knee contribution to total power also increased (Lenton et al, 2019). However, during the walk-run transition the contribution of hip power to total power was reduced, with no effect on power when running while carrying body armour and backpack loads (Brown et al, 2014).…”

“…Ankle peak plantarflexion moment (Quesada et al, 2000;Rice et al, 2017;Seay et al, 2014) also increases with added load to produce the necessary propulsive force to overcome the added inertia. This is reflected in the increase in sagittal plane hip, knee and ankle power generation and the increased contribution of hip and knee power to total power reducing the contribution of the ankle, possibly due to the combat boots worn limiting the range of motion and potential adaptation of power generation (Lenton et al, 2019). A consequence of the increased joint moments in loaded conditions is that knee joint contact forces also increase which leads to a greater risk of acute and chronic musculoskeletal injuries (Lenton et al, 2018).…”

Load Magnitude and Locomotion Pattern Alter Locomotor System Function in Healthy Young Adult Women

“…To date a load magnitude perturbation is evidenced only in terms of increased mechanical [greater ground reaction forces (GRF) ( Birrell et al, 2007 ; Seay et al, 2014b ) and joint kinetics ( Knapik et al, 2004 ; Seay et al, 2014a , b ; Liew et al, 2016 ; Willy et al, 2016 , 2019 ; Lenton et al, 2019 ; Loverro et al, 2019 ; Wills et al, 2019 ; Krajewski et al, 2020 )] and physiological [increased heart rate and ratings of perceived exertion ( Simpson et al, 2010 , 2011 , 2017 ; Huang and Kuo, 2014 )] demands compared to unloaded bipedal ambulation. The majority of these studies consisted of male dominated samples, leaving females underrepresented in load carriage research ( Loverro et al, 2019 ).…”

The Added Value of Musculoskeletal Simulation for the Study of Physical Performance in Military Tasks

“…Musculoskeletal models have already proven their added value with regard to human movement research in several disciplines, such as sports, ergonomics, product design in industry, and for clinical purposes [ 27 , 28 , 29 , 30 ]. To our knowledge, only Lenton et al [ 31 , 32 , 33 ] used musculoskeletal modeling to determine the effects of load carriage on military performance. However, their study was limited to the use of an optical motion-capture system and force plates, which are impractical for field evaluations.…”