Biomechanical Model Research Articles

Human head-neck model and its application thresholds: a narrative review.

There had been many studies on human head-neck biomechanical models in the last two decades, and the associated modelling techniques were constantly evolving at the same time. Computational approaches had been widely leveraged, in parallel to conventional physical tests, to investigate biomechanics and injuries of the head-neck system in the fields like automotive industry, orthopaedic, sports medicine, etc. The purpose of this manuscript is to provide a global review of the existing knowledge related to the modelling approaches, structural and biomechanical characteristics, validation and application of the present head-neck models. This endeavor aims to support further enhancements and validations in modeling practices, particularly addressing the lack of data for model validation, as well as to prospect the future advances in terms of the topics. Seventy-four models subject to the proposed selection criteria are considered. Based on previously established and validated head-neck computational models, most of the studies performed in-depth investigations of included cases, which revolved around four specific subjects: physio-pathology, treatment evaluation, collision condition, and sports injury. Through the review of the recent 20 years research, the summarized modeling information indicated existing deficiencies and future research topics, as well as provided references for subsequent head-neck model development and application.

Relationship between Pelvic Dimensions and Maximum Traction Forces Required during Parturition in Holstein Cows Using a Biomechanical Obstetric Simulator.

The primary aim of this study was to investigate the effect of the pelvic dimensions of Holstein cows on the traction forces during parturition. Additionally, the relationship between calf measurements and traction forces was explored. For this purpose, a modified in vitro biomechanical model simulating obstetric tractions was used. For the requirements of the experiment, six bone pelvises of deceased Holstein cows were collected based on their estimated pelvic inlet area (EPA) and prepared. Additionally, six stillborn calves were collected based on their body weight (BW). The parameters of the pelvic inlet and cavity were measured using computed tomography (CT). Using the simulator, every calf was pulled in a random order through all pelvises, realizing a total of 36 obstetrical tractions, and the required forces were documented with appropriate software. In each extraction, three peaks of forces were recorded, with the first peak occurring at the entrance of the elbows into the maternal pelvic cavity, the second peak at the entrance of the thorax, and the third at the entrance of the calf's pelvis. Logistic regression revealed an exponential relationship between pelvic parameters and traction forces for the entrance of the elbows and the pelvis, with the recorded forces being higher in the two smallest pelvises and stabilizing at a lower level thereafter, while for the entrance of the thorax, the correlations were either exponential or linear. The adjusted coefficients of determination (r2) were generally above the threshold of 0.5 for the entrance of the elbows and pelvis and lower (0.3-0.4) regarding the thorax and were statistically significant (p < 0.05) in all cases. Regarding the relationships between the calf dimensions and the required traction forces, the types of correlations were primarily linear and of lower magnitude. The combination of pelvic and calf parameters in a multivariate model resulted in an r2 of 0.72 for the entrance of the elbows using the pelvic diagonal and calf's body weight, an r2 of 0.62 using the pelvic area and calf's thoracic circumference, and an r2 of 0.75 using the pelvic diagonal and calf's fetlock joint width. In conclusion, under the conditions of the present experimentation, the applied traction forces were mainly influenced by the pelvic dimensions in an exponential manner, whereas the calf body measurements showed a weaker effect. Based on these findings, critical cut-off points exist, different for every pelvic parameter, below which a significant increase in the required traction forces is expected.

Suction Feeding Turned on Its Head: A Functional Novelty Facilitates Lower Jaw Protrusion.

Functional novelties play important roles in creating new ways for organisms to access resources. In fishes, jaw protrusion has been attributed to the massive diversity of suction-based feeding systems, facilitating the dominant mode of prey capture in this group. Nearly all fishes that feed by suction use upper jaw protrusion, achieved by rotation of the mandible at its base, which then transmits forward motion to independently mobile upper jaw bones. In this study, by contrast, we explore an unusual form of lower jaw protrusion in the freshwater invertivore, Nannocharax fasciatus, enabled by a novel intramandibular joint (IMJ). We combine morphological, kinematic, and biomechanical data to show that the added mobility created by the IMJ influences the pattern of suction-based prey capture movements and contributes to lower jaw protrusion (increasing it by 25%, based on biomechanical modeling). Interestingly, the upper jaw bones are fused in N. fasciatus and rotate about a single fixed joint, like the lower jaws of most other suction feeding fishes. We suggest that this vertical inversion of the jaw protrusion mechanism for ventrally directed suction-feeding on benthic prey is a likely exaptation, as the IMJ is used for biting in related taxa. This work highlights the ability of novelties to facilitate ecological specialization by enabling new functional capabilities.

The Compartmental Tongue.

Tongue anatomy and function is widely described as consisting of four extrinsic muscles to control position and four intrinsic muscles to control shape. This myoarchitecture cannot, however, explain independent tongue body and blade movement nor accurately model the subtlety of observed lingual shapes. This study presents the case for a finer neuromuscular structure and functional description. Using the theoretical framework of the partitioning hypothesis, evidence for neuromuscular compartments of each of the lingual muscles was discerned by reviewing studies of lingual anatomy, hypoglossal nerve staining, hypoglossal motoneuron axon tracing, muscle fiber type distribution, and electromyography. Muscle fibers of the visible human female were manually traced to produce a three-dimensional atlas of muscular compartments. A kinematic study was undertaken to determine the degree of independent movement between different parts of the tongue. A simple biomechanical model was used to demonstrate how synergistic groups of compartments can control sectors of the tongue. Results indicated as many as 10 compartments of genioglossus, two each of superior and inferior longitudinal, eight of styloglossus, three of hyoglossus, and six each of transversus and verticalis, while palatoglossus may not have a significant role in tongue function. Kinematic analysis indicated independent control of five sectors of the tongue body, and biomechanical modeling demonstrated how this control may be achieved. Evidence is presented for a lingual structure based on neuromuscular compartments, which work together to position and shape sectors of the tongue and independently control tongue body and blade.

Note on hydrostatic skeletons: muscles operating within a pressurized environment.

Muscles and muscle fibers are volume-constant constructs that deform when contracted and develop internal pressures. However, muscles embedded in hydrostatic skeletons are also exposed to external pressures generated by their activity. For two examples, the pressure generation in spiders and in annelids, we used simplified biomechanical models to demonstrate that high intracellular pressures diminishing the resulting tensile stress of the muscle fibers are avoided in the hydrostatic skeleton. The findings are relevant for a better understanding of the design and functionality of biological hydrostatic skeletons.

A method for calculating vector forces at human-mattress interface during sleeping positions utilizing image registration

The vector forces at the human-mattress interface are not only crucial for understanding the distribution of vertical and shear forces exerted on the human body during sleep but also serves as a significant input for biomechanical models of sleeping positions, whose accuracy determines the credibility of predicting musculoskeletal system loads. In this study, we introduce a novel method for calculating the interface vector forces. By recording indentations after supine and lateral positions using a vacuum mattress and 3D scanner, we utilize image registration techniques to align body pressure distribution with the mattress deformation scanning images, thereby calculating the vector force values for each unit area (36.25 mm × 36.25 mm). This method was validated through five participants attendance from two perspectives, revealing that (1) the mean summation of the vertical force components is 98.67% ± 7.21% body weight, exhibiting good consistency, and mean ratio of horizontal component force to body weight is 2.18% ± 1.77%. (2) the predicted muscle activity using the vector forces as input to the sleep position model aligns with the measured muscle activity (%MVC), with correlation coefficient over 0.7. The proposed method contributes to the vector force distribution understanding and the analysis of musculoskeletal loads during sleep, providing valuable insights for mattress design and evaluation.

Second harmonic generation microscopy, biaxial mechanical tests and fiber dispersion models in human skin biomechanics

Advanced numerical simulations of the mechanical behavior of human skin require thorough calibration of the material’s constitutive models based on experimental ex vivo mechanical tests along with images of tissue microstructure for a variety of biomedical applications. In this work, a total of 14 human healthy skin samples and 4 additional scarred skin samples were experimentally analyzed to gain deep insights into the biomechanics of human skin. In particular, second harmonic generation (SHG) microscopy was used to extract detailed images of the distribution of collagen fibers, which were subsequently processed using a three-dimensional Fourier transform-based method recently proposed by the authors to quantify the distribution of fiber orientations. Mechanical tests under both biaxial and uniaxial loading were performed to calibrate the relevant mechanical parameters of two widely used constitutive models of soft fiber-reinforced biological tissues that account for non-symmetrical fiber dispersion. The calibration of the models allowed us to identify correlations between the mechanical parameters of the constitutive models considered. Statement of significanceConstitutive models for soft collagenous tissues can accurately reproduce the complex nonlinear and anisotropic mechanical behavior of skin. However, a comprehensive analysis of both microstructural and mechanical parameters is still missing for human skin. In this study, these parameters are determined by combining biaxial mechanical tests and SHG stacks of collagen fibers on ex vivo healthy human skin samples. The constitutive parameters are provided for two widely used hyperelastic models and enable accurate characterization of skin mechanical behavior for advanced numerical simulations.

A Novel Bone-Screw-Fastener Demonstrates Greater Maximum Compression Force Before Failure Compared With a Traditional Buttress Screw.

This study compared the maximal compression force before thread stripping of the novel bone-screw-fastener (BSF) with the traditional buttress screw (TBS) in synthetic osteoporotic and cadaveric bone models. The maximum compression force of the plate-bone interface before loss of screw purchase during screw tightening was measured between self-tapping 3.5-mm BSF and 3.5-mm TBS using calibrated load cells. Three synthetic biomechanical models were used: a synthetic osteoporotic diaphysis (model 1), a 3-layer biomechanical polyurethane foam with 50-10-50 pounds-per-cubic-foot layering (model 2), and a 3-layer polyurethane foam with 50-15-50 pounds-per-cubic-foot layering (model 3). For the cadaveric metaphyseal model, 3 sets of cadaveric tibial plafonds and 3 sets of cadaveric tibial plateaus were used. A plate with sensors between the bone and plate interface was used to measure compression force during screw tightening in the synthetic bone models, while an annular load cell that measured screw compression as it slid through a guide was used to measure compression in the cadaver models. Across all synthetic osteoporotic bone models, the BSF demonstrated greater maximal compression force before stripping compared with the TBS [model 1, 155.51 N (SD = 7.77 N) versus 138.78 N (SD = 12.74 N), P = 0.036; model 2, 218.14 N (SD = 14.15 N) versus 110.23 N (SD = 8.00 N), P < 0.001; model 3, 382.72 N (SD = 20.15) versus 341.09 N (SD = 15.57 N), P = 0.003]. The BSF had greater maximal compression force for the overall cadaver trials, the tibial plafond trials, and the tibial plateau trials [overall, 111.27 N vs. 97.54 N (SD 32.32 N), P = 0.002; plafond, 149.6 N versus 132.92 N (SD 31.32 N), P = 0.006; plateau, 81.33 N versus 69.89 N (SD 33.38 N), P = 0.03]. The novel bone-screw-fastener generated 11%-65% greater maximal compression force than the TBS in synthetic osteoporotic and cadaveric metaphyseal bone models. A greater compression force may increase construct stability, facilitate early weight-bearing, and reduce construct failure.

Whipstitch and Locking Stitch Show Equivalent Elongation and Load to Failure Across 3 Suture Systems in a Biomechanical Model of Quadriceps Tendon Grafts for Anterior Cruciate Ligament Reconstruction

PurposeThe purpose of this study was to compare the biomechanical properties of quadriceps tendon (QT) graft stitch methods using three different suture systems for anterior cruciate ligament (ACL) reconstruction. MethodsA total of 48 QTs were harvested from cadaveric knee specimens (age: 73 ± 7 years; range 66-86 years). Samples were randomly divided into three groups where different suture needle systems were used to create two stitch methods: whip stitch (WS) and locking stitch (LS). Surgeons performed each technique to five stitches, each 0.5cm apart. Stitching time was recorded. Samples were pre-conditioned then underwent cyclic loading, followed by load-to-failure. Stiffness (N/mm), ultimate failure load (N), peak-to-peak displacement (mm), elongation (mm), and failure displacement (mm) were recorded. ResultsWS and LS were equivalent across stiffness, ultimate load and peak to peak displacement within Groups 2 and 3. In Group 1, the LS was stiffer than the WS, however the WS achieved a higher ultimate load. For all Groups, the LS achieved lower elongation and failure displacement than the WS, with significant differences in Group 1 and 2. Within each stitching method, equivalence was determined for total elongation and ultimate failure load for all three suture system groups. For WS samples, Group 1 all failed from suture breakage, and both Groups 2 and 3 had instances of failure from suture pull through. All LS samples failed from suture breakage. ConclusionBoth LS and WS provide adequate mechanical properties in each of the three suture systems. Differences in performance do exist; however, each method shows equivalent total elongation and ultimate failure load for all three suture systems. LS may be preferred versus WS due to lower mean elongation and failure displacement. Clinical RelevanceThere is an increased use of a quadriceps tendon (QT) grafts in ACL reconstruction. However, there has been a limited number of studies comparing various stitching methods and optimizing techniques for QT graft fixation. This study may provide important information to surgeons about which suture techniques have better biomechanical profiles.

Torsional stability of fixation methods in basicervical femoral neck fractures: a biomechanical study

BackgroundBasicervical femoral neck fracture is a rare proximal femur fracture with a high implant failure rate. Biomechanical comparisons between cephalomedullary nails (CMNs) and dynamic hip screws (DHSs) under torsion loading are lacking. This study compared the biomechanical performance of three fixations for basicervical femoral neck fractures under torsion load during early ambulation.MethodsThe biomechanical study models used three fixations: a DHS, a DHS with an anti-rotation screw, and a short CMN. Finite element analysis was used to simulate hip rotation with muscle forces related to leg swing applied to the femur. The equivalent von Mises stress (EQV) on fixation, fragment displacement, and strain energy density at the proximal cancellous bone were monitored for fixation stability.ResultsThe EQV of the short CMN construct (304.63 MPa) was comparable to that of the titanium DHS construct (293.39 MPa) and greater than that of the titanium DHS with an anti-rotation screw construct (200.94 MPa). The proximal fragment displacement in the short CMN construct was approximately 0.13 mm, the greatest among the constructs. The risk of screw cutout for the lag screw in short CMNs was 3.1–5.8 times greater than that for DHSs and DHSs with anti-rotation screw constructs.ConclusionsTitanium DHS combined with an anti-rotation screw provided lower fragment displacement, stress, and strain energy density in the femoral head than the other fixations under torsion load. Basicervical femoral neck fracture treated with CMNs may increase the risk of lag screw cutout.Graphical abstract

Three ways to confirm the correctness of the biomechanical model of the morphogenesis of spiral phyllotaxis

The mystery of the phyllotaxis phenomenon has been inspiring inquiry among generations of botanists and mathematicians. Of particular interest is the fact that the number of visible spirals is equal to the numbers from the Fibonacci series. The article proposes three methods to prove the adequacy of the biomechanical model of the morphogenesis of spiral phyllotaxis: mathematical, simulation software, and experimental. Evidence of the biomechanical model leads to a critical rethinking of the understanding of plant morphogenesis.

Biomechanical perspectives on bio-molecular environmental regulation: Long-term strategies

Environmentally conscious practices can be encouraged in many organisations through this study, which has the potential to change our understanding of bio-molecular interactions in natural systems. There is an immediate need for innovative approaches to environmentally responsible bio-molecule management due to the critical nature of environmental problems such as pollution, climate change, and resource depletion. Using state-of-the-art computational biomechanics and organic sciences, this study presents an approach to environmental governance known as Integrative Biomechanical Modelling for Environmental Governance Technique (IBM-EGT). A combination of environmental parameterization, advanced biomechanical modelling, and excellent data sets allows the IBM-EGT method to describe the behaviour of biomolecules in a wide variety of natural settings. By factoring in environmental variables like temperature, pH, and pollutant concentrations, IBM-EGT provides a comprehensive picture of bio-molecular dynamics in response to environmental stimuli. Biomaterials, bioremediation, pharmaceuticals, and even agriculture are just a few of the many potential sectors that can profit from IBM-EGT. Agricultural operations can be optimised, green medicines can be introduced, sustainable biomaterials can be developed, and diseased regions can be cleaned up with its help. Because it enables the prediction of bio-molecular interactions and behaviour in complex environmental contexts, simulation analysis is a fundamental topic of IBM-EGT. In an effort to find the best ways to conduct activities while reducing negative environmental impacts and increasing positive ones, IBM-EGT does scenario analysis based on simulations. The studies mentioned here help keep the environment and people healthy by elucidating the nature of the connection between Bio-Molecules and their herbal environment. Furthermore, it enables the development of plans for the distant future.

Optimization of traction parameters for lumbar scoliosis

BackgroundScoliosis is a high incidence disease that endangers the physical and mental health of adolescents. Traction therapy, as a conservative treatment plan, is helpful to improve the recovery speed of patients by studying the influence of different traction factors on the therapeutic effect.MethodsBased on the thin layer CT data of the lumbar spine of a 16-year-old patient with scoliosis, Mimics21.0 was used to extract the 3D digital model, and Geomagic Wrap2021 was used to perform the smooth surface. After that, SolidWorks was used to manually construct the structures, such as the intervertebral disc, and Ansys17.0 was used to add constraints, ligaments, and other features. Three-factor ANOVA was carried out after an orthogonal experiment that considered traction mode, traction angle, and traction force was finished.Results① A three-dimensional biomechanical model of lumbar scoliosis was created. ② The model’s correctness was confirmed by comparing it to the corpse and other finite element models, as well as by verifying it under a range of working settings. ③ Traction force (P = 0.000), traction angle (P = 0.000), the interaction between traction force and traction angle (P = 0.000), and the interaction between traction mode and traction angle (P = 0.045) were all significant. ④ The interaction between traction force and traction angle has the most significant effect on Cobb, and traction with a certain angle is better than traditional axial traction. ⑤ Traction mode is not significant, but the interaction between traction mode and traction angle is significant.ConclusionsA certain angle of traction can aid in improving outcomes and the traction force can be suitably decreased in the clinical formulation of the traction plan. The uniformity of correcting effect is more favorable when higher fixation techniques like positive suspension or traction bed traction are used, as opposed to overhanging traction.

Design and evaluation of the OmniSuit: A passive occupational exoskeleton for back and shoulder support

Many physically straining occupations involve lifting movements over the full-vertical range of motion, which over time may lead to the development of musculoskeletal injuries. To address this, occupational exoskeletons can be designed to provide meaningful support to the back and shoulders during lifting movements.This paper introduces the main functional design features of the OmniSuit, a novel passive occupational exoskeleton. We present the technical and biomechanical considerations for the expected support level, as well as an evaluation of the physiological benefit and usability of the exoskeleton in a sample of 31 healthy volunteers performing physically demanding tasks in a laboratory setting.The OmniSuit exoskeleton significantly reduced Deltoid, Trapezius and Erector Spinae muscle activity between 4.1%MVC and 15.7%MVC when lifting a 2.5kg weight above shoulder level (p<0.001), corresponding to a reduction of up to 49.1% compared to without exoskeleton. A position-dependent reduction of Erector Spinae muscle activity was observed (p<0.001), with reductions ranging between 4.6%MVC and 14.0%MVC during leaning and squatting, corresponding to a reduction up to 41.5% compared to without exoskeleton. The measured muscular support and the predicted support torque based on the biomechanical model were found to show a similar profile for those phases of the movement which are most straining to the shoulder and back muscles. Participants reported experiencing good device usability and minimal discomfort (<1/10) in the shoulder and back during task execution with exoskeleton support.These first results validate that the considered biomechanical model helped design an ergonomic and efficient exoskeleton, and confirm the potential of such wearable assistive devices to provide support over multiple joints during physically demanding tasks.

Effect of occlusal contact on TMJ loading during occlusion: An in silico study

Alterations in occlusal features may have significant consequences, ranging from dental aesthetics to health issues. Temporomandibular joint disorders (TMDs) are often associated with joint overload, and the correlation between occlusal features and TMDs has been thoroughly discussed. In current work, we introduced a novel stomatognathic model that aligns well with in vivo experimental measurements, specifically designed to decouple the impact of occlusal contact and periodontal ligament (PDL) negative feedback on temporomandibular joint (TMJ) loading. Utilizing an in-silico approach, the simulation analysis included six symmetric occlusal contact scenarios. Furthermore, a biomechanical lever model was employed to clarify the mechanical mechanism and investigate the multi-factorial effects of TMJ overload. These findings indicate that anterior shifts in the occlusal centre lead to increased TMJ loading, particularly in occlusal contact cases with anteroposterior changes. Considering the symmetrical distribution of occlusal contact, mediolateral alterations had a more modest effect on TMJ loading. Additionally, potential negative feedback activated by principal strain of periodontal could not only alleviate joint load but also diminish occlusal force. These investigations enhance our understanding of the intricate interactions between masticatory muscles, occlusal forces, and joint contact forces, thereby providing motivation for future comprehensive studies on TMJ biomechanical overload.

Biomechanics of annulus fibrosus: Elastic fiber simplification and degenerative impact on damage initiation and propagation

This study addresses three primary objectives related to lumbar intervertebral disc (IVD) biomechanics under ramping quasi-static loading conditions. First, we explore the conditions justifying the simplification of axisymmetric elastic fiber families into single fiber bundles through discretized strain energy functions. Simulations reveal that a concentration factor exceeding 10 allows for a consistent deviation below 10% between simplified and non-simplified responses. Second, we investigate the impact of elastic fibers on the physiological stiffness in IVDs, revealing minimal influence on biological motions but significant effects on degeneration. Lastly, we examine the initiation and progression of annulus fibrosus (AF) damage. Our findings confirm the validity of simplifying elastic fiber families and underscore the necessity of considering elastic fiber damage in biomechanical studies of AF tissues. Elastic fibers contribute to increased biaxial stretch stiffness, and their damage significantly affects the loading capacity of the inner AF. Additionally, degeneration significantly alters the susceptibility to damage in the AF, with specific regions exhibiting higher vulnerability. Damage tends to extend circumferentially and radially, emphasizing the regional variations in collagen and elastic fiber properties. This study offers useful insights for refining biomechanical models, paving the way for a more comprehensive understanding of IVD responses and potential clinical implications.

Detailed development and validation of a finite element model for studying the entire spinal vibration behavior within a seated human body

Studying the vibration behavior of the entire spine can guide the design of seat comfort and vibration safety. However, due to simplification of traditional biomechanical models, very few studies have analyzed in detail the vibration behavior characteristics of the entire spine inside a seated human body. Therefore, this study aimed to provide guidance and reference for spinal modeling and biomechanical research in ergonomics. A developed finite element model of three-dimensional seated human body was validated and adjusted based on anatomical data of human spine in detail. Static analysis, modal analysis and random response analysis (under vertical excitation between 0 and 20 Hz at 1 m/s2 r.m.s.) were conducted. The range of motion, modal frequencies and the tri-axial transmissibility of the developed models matched well with experimental results. In the vertical resonance mode, the entire spine contained both vertical deformation (60% of the total) and vertical displacement (40%), in addition, the cervical spine, especially the lumbar spine, also contained bending deformation which could alleviate the impact, but led to complex alternating stresses, increasing the risks of the spinal injuries under vertical whole-body vibration. From the bottom to the top of the spine, the frequency distribution of vertical transmissibility became steeper, the peak value increased, and the number of peaks decreased. This study provided new insights into the vibration behavior and frequency response of the entire spine inside a seated human body for improving seat comfort and vibration safety.

Towards the biomechanical modelling of the behaviour of ex-vivo porcine perineal tissues

The perineum is a layered soft tissue structure with mechanical properties that maintain the integrity of the pelvic floor. During childbirth, the perineum undergoes significant deformation that often results in tears of various degrees of severity. To better understand the mechanisms underlying perineal tears, it is crucial to consider the mechanical properties of the different tissues that make up the perineum. Unfortunately, there is a lack of data on the mechanical properties of the perineum in the literature. The objective of this study is to partly fill these gaps. Hence sow perineums were dissected and the five perineal tissues involved in tears were characterized by uniaxial tension tests: Skin, Vagina, External Anal Sphincter, Internal Anal Sphincter and Anal Mucosa. From our knowledge, this study is the first to investigate all these tissues and to design a testing protocol to characterize their material properties. Six material models were used to fit the experimental data and the correlation between experimental and predicted data was evaluated for comparison. As a result, even if the tissues are of different nature, the best correlation was obtained with the Yeoh and Martins material models for all tissues. Moreover, these preliminary results show the difference in stiffness between the tissues which indicates that they might have different roles in the structure. These obtained results will serve as a basis to design an improved experimental protocol for a more robust structural model of the porcine perineum that can be used for the human perineum to predict perineal tears.

Metabolic Allometric Scaling of Multicellular Organisms as a Product of Evolutionary Development and Optimization of Food Chains

Production of energy is a foundation of life. The metabolic rate of organisms (amount of energy produced per unit time) generally increases slower than organisms’ mass, which has important implications for life organization. This phenomenon, when considered across different taxa, is called interspecific allometric scaling. Its origin has puzzled scientists for many decades, and still is considered unknown. In this paper, we posit that natural selection, as determined by evolutionary pressures, leads to distribution of resources, and accordingly energy, within a food chain, which is optimal from the perspective of stability of the food chain, when each species has sufficient amount of resources for continuous reproduction, but not too much to jeopardize existence of other species. Metabolic allometric scaling (MAS) is then a quantitative representation of this optimal distribution. Taking locomotion and the primary mechanism for distribution of energy, we developed a biomechanical model to find energy expenditures, considering limb length, skeleton mass and speed. Using the interspecific allometric exponents for these three measures and substituting them into the locomotion-derived model for energy expenditure, we calculated allometric exponents for mammals, reptiles, fish, and birds, and compared these values with allometric exponents derived from experimental observations. The calculated allometric exponents were nearly identical to experimentally observed exponents for mammals, and very close for fish, reptiles and the basal metabolic rate (BMR) of birds. The main result of the study is that the MAS is a function of a mechanism of optimal energy distribution between the species of a food chain. This optimized sharing of common resources provides stability of a food chain for a given habitat and is guided by evolutionary pressures and natural selection.

Study on physiological injuries of occupants under vertical impact loads

Under vertical impact loads, such as explosions, serious compressive deformation occurs in the pelvic bones and lumbar vertebrae of the human body leading to injuries or fatalities for occupants. This study focuses on the occupant-seat model in military vehicles, establishes a biomechanical model of the human spine, and establishes the relationship between vertical impact loads and human injuries. Subsequently, a C-shaped energy-absorbing cushioning structure is designed for application at the bottom support of the seat. Using a peak value of 50 g explosion-simulated triangular wave loading, the study compares the attenuation effects of different structural characteristics of cushioning energy-absorbing structures on impact loads. The results indicate that a 50 g peak vertical impact load can cause significant human injuries. The designed energy-absorbing cushioning structure can greatly reduce human response, but both excessively soft and rigid energy-absorbing cushioning structures fail to achieve effective impact attenuation.