| Objective:Sports shoe is the equipment that most closely related to sports.The modern running shoes are designed to protect the feet.But the rate of running-related injuries has not decreased since the invention of running shoes.The "mismatch" between the mechanical environment created by running shoes and the structure and function of human feet may be one of the reasons for the high incidence of running-related injuries.If we want to explore the mechanism of running injury,understanding the evolution of the human foot structure is crucial.Based on the principle of "function follows form",this study used 3D reconstruction technology and the finite element analysis to explore the corresponding relationship between metatarsal structure and function from the evolutionary perspective,and further explored the role of the fourth metatarsal in the evolution of the arch,providing new ideas for the design of running shoes.Content:This study is divided into four sections.The first part is to investigate the influence of anisotropic voxel caused by field of view setting on the accuracy of three-dimensional reconstruction of bone geometric models,providing a guarantee for the reliability of the finite element analysis results of the fourth metatarsal bone.The second part is to establish the index system of geometric and inertia parameters,analyzing the sexual dimorphism of metatarsals of modern human.The third part is to explore the evolution of the fourth metatarsal of modern human,and explored the potential bearing mode of the arch related to the fourth metatarsal.The fourth part is to design,trial-produce and test running shoes according to the locomotion characteristics and requirements of the foot arch.Methods:For the first part,CT scans were used to scan six subjects’ foot twice with an interval of 18 months with different fields of view,and 120 metatarsals were constructed using Mimics software.The body coordinate system of bone was employed to align the metatarsals.The differences of geometric parameters,the gray value and three principal moments of inertia of reconstructed bone model with anisotropic voxel induced by the field of view setting were compared.For the second part,30 young males and 30 young females were chosen.CT scans were used to examine the subject’s foot.600 metatarsals were reconstructed using Mimics software,and the metatarsals were aligned using the body coordinate system of bone.The reconstructed metatarsal model’s geometric characteristics(bone length,width,height,volume,surface area)and gray values were recovered,and the surface area-volume ratio,bone density,and principal moment of inertia were calculated.The parameters were normalized.The independent sample T test was performed to compare the sexual differences of parameters.Sexual dimorphism indexes of parameters were computed.Finally,the sexual dimorphism functions were established by combining parameters of geometric,density and moment of inertia to explore sexual differences in the morphology and structure of the metatarsal.For the third part,the geometric model of the fourth metatarsal of 60 subjects from the second part,and the fourth metatarsal models of G.gorilla,P.troglodytes,A.afarensis,and H.naledi were included and reconstructed.Material properties were given to the model.The constraint conditions of the model were set according to the anatomical structure between the fourth metatarsal and cuboid,and the structure between lateral cuneiform and the fourth proximal phalangeal.Finally,the loading conditions were set according to the loading of fourth metatarsal of modern human during bipedal locomotion.The finite element analysis was performed for the fourth metatarsal according the boundary conditions,and the discrimination index systems of species were established based on the geometric characteristics of the metatarsal and the results of finite element analysis.The fourth part was to design the structure of carbon fiber plate based on the lateral foot strike pattern.The finite element models of carbon plate of running shoes were established,and the finite element analysis of carbon plate was carried out at the time of loading response,maximum loading and roll-off of running.To verify the finite element simulation analysis results,the designed shoes were pre-produced and 30 subjects with lateral foot strike pattern were invited to test the designed running shoes.The gait data of subjects were collected and compared while they wore the designed running shoes and Nike Vaporfly shoes.Results:1.No significant difference in bone length,width,height,volume,surface area and the three principal moments of inertia of bone models which was reconstructed using anisotropic voxels caused by field of view setting at the sub-millimeter scale(p>0.05).Significant difference was found in the gray value(p<0.01).2.Significant sexual differences in the bone length,width,height,surface area-to-volume ratio and the three principal moments of inertia of metatarsals(p<0.05).The highest sexual dimorphism was found in surface area-to-volume ratio,principal moment of inertia around the z axis and bone height.The accuracy of sexual discrimination functions established based on metatarsal geometric and inertial parameters were between 88.3%-98.3%.The discriminant functions based on parameters of the third metatarsal and the fourth metatarsal of right side exhibited the highest accuracy with 98.3%.3.Highly significant sexual differences were found in normalized bone height,surface area,and volume of the metatarsals(p<0.01);A.afarensis had much larger values of bone width,height,volume,and surface area than those of G.gorilla s,P.troglodytes,and H.naledi,closing to modern male’s values.H.naledi,on the other hand,had significantly smaller values of bone height and width than those of modern humans,and the volume and surface area were comparable to those of modern female.Geometric values of the fourth metatarsal of P.troglodytes were similar to the values of G.gorilla ’s.The surface area of a G.gorilla ’s fourth metatarsal was close to that of modern human,but the volume was substantially smaller.The volume and surface area of P.troglodytes were much smaller than those of modern human,and the values were the smallest among the tested species.The finite element results showed that the maximum value of von-Mises stress,maximum shear stress,maximum principal stress,and minimum value of minimum principal stress of the modern human’s fourth metatarsal were the smallest among all tested species,followed by the G.gorilla,and the values of P.troglodytes were the largest.The values of A.afarensis and H.naledi were very close to those of modern humans.The relationship between loading angle and the magnitude of the stress showed as: the stress gradually decreased as the loading angle increased.There were significant differences in the stress results between male and female when loading in the sagittal planes(p<0.05).The combination of stress indexes performed better than the combination of geometric indexes when it comes to identifying P.troglodytes,G.gorilla,and modern human.The use of a combination of stress indexes of the fourth metatarsal loaded on the horizontal plane can distinguish modern human from G.gorilla and P.troglodytes.The values of A.afarensis and H.naledi always fell within the average value range of modern human,when using combinations that included von-Mises stress,maximum shear stress,and minimum principal stress.4.The results of finite element analysis showed that the von-Mises stress was concentrated in the middle of forefoot of carbon fibre plate at different times in a single running cycle,and the peak value of von-Mises stress on the lower surface of scoop-shaped carbon fibre plate appeared at the area of pressure bar.The peak value of von-Mises stress on scoop-shaped carbon fibre plate was larger than that on Nike Vaporfly carbon fibre plate.The scoop-shaped carbon fiber plate that designed according to the lateral foot strike pattern increased the percentage of swing phase in a running cycle,decreased the length of gait line;furthermore,it reduced the maximum force of the foot and significantly increased the peak pressure of the forefoot.Conclusions:1.This study found that anisotropic voxel-based reconstructed bone models are accurate and credible at the sub-millimeter scale.The accurate bone models pave the way for the following finite element analysis.2.The geometric characteristics and principal moment of inertia of human metatarsal bone have sexual dimorphism and can be used for sex estimation.Combining the metatarsal geometric parameters with the principal moments of inertia,we can accurately estimate the sex of individuals,providing a new method for anthropological research.3.The metatarsal structure of the modern human is better than that of P.troglodytes,G.gorilla and early hominins(A.afarensis and H.naledi)in axial compression loading bearing,reflecting the directional adaptation of the fourth metatarsal structure of modern human to savanna-based activities.The simulation analysis of the axial loading capacity of the metatarsal bone of hominins(A.afarensis,H.naledi and modern human),P.troglodytes and G.gorilla s reveals the role of the fourth metatarsal in the evolution of the foot arch and provides evidence for determining the locomotion characteristics and needs of the fourth metatarsal.4.The sexual differences were found in the stress in sagittal plane of metatarsal structures.The combinations of stress indexes of the fourth metatarsal on the horizontal plane can distinguish modern human from G.gorilla and P.troglodytes.The stress performances of the metatarsal structure of A.afarensis and H.naledi were closer to modern human when using the combinations containing von-Mises stress,maximum shear stress and minimum principal stress,providing a new perspective and method for the inference of fossil locomotion behavior.5.The scoop-shaped carbon fiber plate helps to increase the percentage of swing phase in a running cycle and the peak pressure of the forefoot.The design of scoop-shaped carbon fibre plate conforms to the loading condition of shoe-floor during running and optimizes the action area of plantar pressure,which effectively improves the ergonomics of human movement in endurance running. |
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