Influence of combat boot types on in-shoe forces and perceived comfort during unloaded and loaded walking

Abstract

IntroductionCombat boots are essential protective gear for military personnel. The purposes of the present study were to examine (1) the influence of combat boot type on ground reaction force (GRF) variables and perceived comfort during unloaded and loaded walking and (2) the relationship between comfort and biomechanical measurements.MethodsFour types of combat boots with different physical features (eg, mass, thickness) and mechanical properties (eg, cushioning, rigidity) were compared across 61 male participants with experience in military marching while carrying heavy loads. In each boot type, participants completed a 10-m walk under an unloaded and a 20-kg loaded conditions at their preferred speeds. Peak force and loading rate during walking were measured using the loadsol wireless in-shoe sensor system. Comfort level was assessed using a 7-point Likert scale. Difference between loaded and unloaded walking, and across boot types were statistically compared. Correlation analyses were performed between comfort and GRF variables.ResultsOn average across all boot types, participants walked 2.1% slower when carrying 20-kg loads while experiencing 24.3% higher peak force and 20.8% higher loading rate. Boot D was perceived as most comfortable, followed by boots C, B and A (χ2(2)=115.4, p<0.001). Participants walked slightly faster (p=0.022, ηp2 = 0.052) and displayed higher loading rates (p<0.001, ηp2=0.194) in the two more comfortable boots (C and D) than the less comfortable boots (A and B). No significant correlations were found between perceived comfort and any GRF variables.ConclusionsCombat boot features can influence perceived comfort ratings substantially during walking, whereas biomechanical differences among boot types are more subtle regardless of load conditions. The lack of relationship between comfort and force variables suggests that both subjective and objective measurements should be considered for comprehensive evaluation of combat boots.

Validation of In-Shoe Force Sensors during Loaded Walking in Military Personnel

“…In the military context, one previous study used the loadsol ® sensors to compare in-shoe forces between different types of combat boots [ 7 ]. This earlier study included a loaded walking condition where participants carried a 20 kg field pack but did not check the validity of the sensors under heavy load situations.…”

“…While a newer version of loadsol ® allows a higher sampling rate of 200 Hz [ 18 ], our laboratory only possessed the earlier model with a maximum rate of 100 Hz. For walking activities in military boots, a sampling rate of 100 Hz has been used in other studies using in-shoe force [ 7 ] or pressure sensors [ 11 ]. Calibration of the sensors was performed using participants’ own body weight following the manufacturer’s guidelines.…”

“…Measuring the ground reaction forces (GRF) during dynamic weight-bearing activities is useful for quantifying the physical loading placed on the human body. In the military context, for instance, previous studies have used GRF measures to evaluate exoskeletons [ 5 , 6 ], combat boots [ 7 , 8 ], and ankle sprain mechanisms [ 9 ].…”

“…This traditional approach to GRF measurement is time-consuming, requires expensive equipment, and often limits testing to laboratory environments. Recent advancement in wearable technology has opened new opportunities for biomechanical and physiological evaluation, including applications in combat boots [ 7 , 11 ]. Different types of technology have shown promising results in the military context, for example, smart clothing for health and safety monitoring [ 12 ], wearables for 24 h heart rate variability monitoring [ 13 ], in-shoe plantar pressure measurement systems for gait analysis [ 11 ], and instrumented socks to provide real-time audio biofeedback for gait re-training in injured military service members [ 14 ].…”

“…There exist many types of military load carriage systems that are designed for specific purposes [ 19 ]. Regardless of the body size of the individuals, soldiers often carry standard-weight military equipment such as backpacks, Kevlar helmets and rifles [ 1 , 7 , 19 , 20 ]. As the loadsol ® in-shoe force sensors are calibrated using the wearer’s own body weight, the accuracy of the sensors may be affected by the additional load soldiers have to carry.…”