ERGOnomics TECHnologies Miss. Natalie Ross A-TEMP-009 -1 ISSUE 002 An investigation into the biomechanical impact of military combat boots 14 September 2017

Background Lower limb injuries remain a significant factor impacting military personnel and combat readiness Overuse injuries that worsen with repeated exposure to stress Footwear design is a major factor influencing injury mechanisms of lower limbs – little attention from military stand point Training and operational activities of soldiers typically performed in combat boots – suspected that design features may contribute to injury Belief is presented in literature for advantages for performing military training activities in running shoes as opposed to combat boots Only one study has compared injury incidence between military boots and running shoes (Knapik et al., 2015). No biomechanical comparison

Background Designed to provide protection and increased stability over unpredictable terrains: Stiffer boot shaft Stronger material make-up Stiffer mid-sole Increased traction properties

? ? Background Durability Thicker material Protection Stiffer mid-sole Torsional stability Protective functions Stiffer boot shaft Ankle stability Traction properties Increased grip Increased mass ? ? Muscle activity Limited ankle range of motion Biomechanical consequences Ground reaction forces Injury risk Decreased shock absorption Contact pressure

Background Aim was to compare the biomechanical responses of soldiers walking in running shoes to military boots

Experimental design Lab based study 22 injury free male soldiers Gradient % -10 10 Footwear Barefoot Running shoes Military combat boots

Ground reaction forces Dependent variables Ground reaction forces Impact peak Peak loading rate Propulsive peak Braking peak Bertec Instrumented Treadmill Muscle activity Rectus femoris Biceps femoris Gastrocnemius Tibialis anterior Delsys Wireless EMG Pressure analysis Peak contact pressure at foot-shoe interface Tekscan System

Results

Ground reaction forces (GRFs) * * Impact peak Peak loading rate

Ground reaction forces Greater amount of vertical force exerted through the musculoskeletal system More rapidly exerted Increased stress placed onto the joints and soft tissues increasing the risk of injury

Running shoes vs barefoot Muscle activity Downhill Level Uphill Muscle Running shoes vs barefoot Boots vs barefoot Boots vs running shoes Gastrocnemius - Rectus femoris Biceps femoris Tibialis anterior Significant increase No significant change -

Rectus femoris Knee extension during swing, heel strike and support phases Responsible for positioning the foot for landing and controlling weight acceptance Increased muscle activation required for weight acceptance during declined walking in military boots Increased energetic cost

Gastrocnemius Plantar flexion during toe-off Generates forward propulsion of foot Increased propulsive force is required during inclined walking Increased strain on Achilles tendon Increased energetic cost

Pressure analysis * * *

Pressure analysis Significantly higher peak contact pressure Running shoes: Military combat boots: Significantly higher peak contact pressure Pressure map (KPa) at the right shoe-foot interface

Conclusions and recommendations This study provides evidence to support that training in combat boots results in unfavourable biomechanical responses, when compared to training in running shoes: Increased vertical GRFs Increased gastrocnemius muscle activation during inclined walking Increased rectus femoris muscle activation during declined walking Increased plantar pressure at foot-shoe interface at all gradients .

Conclusions and recommendations The study highlights the importance to consider the impact of footwear on the energetic cost of locomotion and lower limb injury occurrence among military personnel. These factors should be considered for optimal shoe design Emphasis should be placed on reducing the mass of military combat boots as well as providing improved shock absorption properties to help distribute plantar pressure and transmission of ground reaction forces. The use of running shoes should be considered for certain military training activities as opposed to military boots. Future research: analysis of hip, knee and ankle kinematic data .