Hip width and metabolic energy expenditure of abductor muscles.

Despite a paucity of physiological evidence, simplistic biomechanical analyses have led researchers to assume that humans who have wider hips use more energy to walk. Pitting biomechanical first principles against physiological data has led to little deepening of our understanding of bipedalism and its evolution. Both approaches, however, use proxies for the energy used by muscles. We decided to approach the question directly. Using a musculoskeletal model of the human body that estimates the metabolic energy expenditure of muscle activation for 48 people (23 women), 752 trials were evaluated. Metabolic energy consumption for the abductor muscles was summed over a stride to create total abductor energy expenditure. We calculated the maximum hip joint moment acting in the coronal plane and the functional distance between the hip joint centers. We hypothesize that wider hips would be correlated with both maximum coronal plane hip moment and increased total abductor energy expenditure when mass and velocity were controlled. Linear regressions with multiple independent variables, clustered by participant to control for the non-independence of the data points, were performed in Stata. We found that hip width does not predict total abductor energy expenditure, although mass and velocity combine to predict 61% of the variation (both p<0.001). Maximum hip joint coronal plane moment is predicted by pelvic width (p<0.001) and, in combination with mass and velocity (both p<0.001), explains 79% of the variation. Our results indicate that people use their morphology in ways that limit differences in energy expenditure. Consistent with recent discussion, intraspecific variation might not be useful to understand differences among species.

Foot morphology influences the change in arch index between standing and walking conditions.

Human foot morphology has been of interest to anatomists, clinicians, and paleontologists for a century due to its importance in bipedal walking. Foot shape changes as forces move through it from the body to the substrate. Although the arch of the foot has been extensively evaluated, the role of foot morphology in the change of the arch height in walking is less explored. To remedy this lacuna, the Arch Indices (AIs) of the left and right feet of 77 people were calculated in double and single stance standing and walking (dynamic) conditions. The feet were categorized into clinical foot types (cavus, normal, planus). The change in static AI between double and single stance was used to predict dynamic AI and the difference between predicted and observed dynamic AI was examined. As expected, AIs increased (i.e., arch height decreased) with increasing load on the foot for the entire sample and each foot type (p's > .001), but the ability of change in static AIs to predict dynamic AI varied among foot types, implicating the possibility of variability in foot mechanics among foot types. While planus feet change stiffness during walking, presumably due to muscular action, cavus feet are more variable in their response to load. Static and dynamic AIs are effective in reflecting the changes in foot stiffness that occur in walking and future work should examine the role of extrinsic muscle activation in this stiffness change.

Sensitivity of musculoskeletal models to variation in muscle architecture parameters.

Musculoskeletal models, like all theoretical models of physical processes, depend on the assumptions needed to construct the model. For musculoskeletal models, these assumptions include, among other things, the kinematic data, the kinetic data and the muscle parameters. The former (dynamic) data can be acquired relatively easily from living subjects, but the latter are usually based on limited information, frequently determined from cadaver studies performed on elderly individuals. Previously, we determined the sensitivity of forces to dynamic differences among 10 humans walking on a straight path. Here, we assess the sensitivity of the muscle and joint reaction forces developed in human walking to variable muscle parameters obtained from 10 living adults, whose data were recently reported, and compared the results with the values from a standard model that depends on cadaveric data. We found that, while the force patterns across the stance cycle were similar among muscle parameter models, differences of as much as 15% in the force magnitude were produced. Whether or not the variation between the standard model and other muscle parameters is important depends on why the forces are required.

Walking Speed Alters Barefoot Gait Coordination and Variability.

Using the dynamic system approach, we examined the pattern and variability of inter-joint coordination in barefoot and shod walking in 20 women at three speeds: SLOW, FAST, and comfortable walking speed (CWS). We found that barefoot and shod walking used different coordination strategies to cope with increasing walking speed. As walking speed increased, ankle-knee coordination patterns between shod and barefoot became less different (p < 0.00001), and ankle-hip coordination patterns became more different (p < 0.001). Compared to shod, barefoot walking had significantly lower coordination variability in mid stance of knee-hip at CWS and FAST and late swing of ankle-hip at SLOW and CWS with medium effect (effect size 0.61-0.74). Future research should investigate the connection between the decreased coordination variability and joint tissue stress to understand the impact of barefoot walking on the lower extremity joints.

Anthroengineering: an independent interdisciplinary field.

In recent decades, funding agencies, institutes and professional bodies have recognized the profound benefits of transdisciplinarity in tackling targeted research questions. However, once questions are answered, the previously abundant support often dissolves. As such, the long-term benefits of these transdisciplinary approaches are never fully achieved. Over the last several decades, the integration of anthropology and engineering through inter- and multidisciplinary work has led to advances in fields such as design, human evolution and medical technologies. The lack of formal recognition, however, of this transdisciplinary approach as a unique entity rather than a useful tool or a subfield makes it difficult for researchers to establish laboratories, secure permanent jobs, fund long-term research programmes and train students in this approach. To facilitate the growth and development and witness the long-term benefits of this approach, we propose the integration of anthropology and engineering be recognized as a new, independent field known as anthroengineering. We present a working definition for anthroengineering and examples of how anthroengineering has been used. We discuss the necessity of recognizing anthroengineering as a unique field and explore potential novel applications. Finally, we discuss the future of anthroengineering, highlighting avenues for moving the field forward.

Consistent inconsistencies in braking: a spatial analysis.

The dynamic system that is the bipedal body in motion is of interest to engineers, clinicians and biological anthropologists alike. Spatial statistics is more familiar to public health researchers as a way of analysing disease clustering and spread; nonetheless, this is a practical approach to the two-dimensional topography of the foot. We quantified the clustering of the centre of pressure (CoP) on the foot for peak braking and propulsive vertical ground reaction forces (GRFs) over multiple, contiguous steps to assess the consistency of the location of peak forces on the foot during walking. The vertical GRFs of 11 participants were collected continuously via a wireless insole system (MoticonReGo AG) across various experimental conditions. We hypothesized that CoPs would cluster in the hindfoot for braking and forefoot for propulsion, and that braking would demonstrate more consistent clustering than propulsion. Contrary to our hypotheses, we found that CoPs during braking are inconsistent in their location, and CoPs during propulsion are more consistent and clustered across all participants and all trials. These results add to our understanding of the applied forces on the foot so that we can better predict fatigue failures and better understand the mechanisms that shaped the modern bipedal form.

A review of musculoskeletal modelling of human locomotion.

Locomotion through the environment is important because movement provides access to key resources, including food, shelter and mates. Central to many locomotion-focused questions is the need to understand internal forces, particularly muscle forces and joint reactions. Musculoskeletal modelling, which typically harnesses the power of inverse dynamics, unites experimental data that are collected on living subjects with virtual models of their morphology. The inputs required for producing good musculoskeletal models include body geometry, muscle parameters, motion variables and ground reaction forces. This methodological approach is critically informed by both biological anthropology, with its focus on variation in human form and function, and mechanical engineering, with a focus on the application of Newtonian mechanics to current problems. Here, we demonstrate the application of a musculoskeletal modelling approach to human walking using the data of a single male subject. Furthermore, we discuss the decisions required to build the model, including how to customize the musculoskeletal model, and suggest cautions that both biological anthropologists and engineers who are interested in this topic should consider.

Muscle forces and the demands of human walking.

Reconstructing the locomotor behavior of extinct animals depends on elucidating the principles that link behavior, function, and morphology, which can only be done using extant animals. Within the human lineage, the evolution of bipedalism represents a critical transition, and evaluating fossil hominins depends on understanding the relationship between lower limb forces and skeletal morphology in living humans. As a step toward that goal, here we use a musculoskeletal model to estimate forces in the lower limb muscles of ten individuals during walking. The purpose is to quantify the consistency, timing, and magnitude of these muscle forces during the stance phase of walking. We find that muscles which act to support or propel the body during walking demonstrate the greatest force magnitudes as well as the highest consistency in the shape of force curves among individuals. Muscles that generate moments in the same direction as, or orthogonal to, the ground reaction force show lower forces of greater variability. These data can be used to define the envelope of load cases that need to be examined in order to understand human lower limb skeletal load bearing.

Radiographic measurements of the talus and calcaneus in the adult pes planus foot type.

OBJECTIVE: A distinctive feature of the modern human foot is the presence of a medial longitudinal arch when weight-bearing. Although the talus and calcaneus play a major role in the structure and function of the human foot, the association between the morphology of these bones and longitudinal arch height has not been fully investigated. A better understanding of this relationship may assist in the interpretation of pedal remains of fossil hominins, where features of the foot and ankle morphology have been described as providing evidence for the presence of a longitudinal arch. METHODS: For this study, weight-bearing radiographs of 103 patients from an urban US Level 1 trauma center, taken as part of a clinical examination for medical evaluation, were selected. These radiographs were classified as to foot type by arch height as defined using the calcaneal inclination angle. From this group, 68 radiographs were suitable for linear and angular measurements of the talus and 74 of the calcaneus. The relationships between these measurements and arch height were explored using least squared linear regression analysis. RESULTS: The results demonstrate that angular measurements of the calcaneus (particularly those that reflect the relationship of the talar articular facets to each other and the tilt of the calcaneocuboid joint to the longitudinal axis of the calcaneus) are predictive of arch height (r2 = .29-.44 p ≤ .001). All angular measurements of the talus and all examined linear measurements of both the talus and calcaneus were not predictive of arch height. DISCUSSION: These results suggest that certain angular measurements of the calcaneus are associated with arch height in the modern human foot. While this information is useful in the interpretation of hominin pedal remains, the relationship of the morphology of these bones, as well as other bones of the foot, to arch height is complex, requiring further investigation.

Estimating the in vivo location of the talus from external surface landmarks.

OBJECTIVES: Finite element analysis has gained popularity in anthropological research to connect morphological form to measurable function but requires that loads are applied at appropriate anatomical locations. This is challenging for the ankle because the joint surfaces are not easily determined given their deep anatomical location. While the location of the talonavicular and subtalar joints can be directly determined via medical imaging, regression equations are a common, less invasive method to estimate joint locations from surface anatomy. We propose a regression-based method to locate the in vivo positions of the talonavicular and subtalar joints employing three-dimensional (3D) surface markers, such as those used routinely in gait studies. METHODS: Navicular height was measured on weight-bearing radiographs (WBR) and simulated weight-bearing computed tomography (SWCT) scans to ensure SWCT correctly simulated foot weight-bearing configuration. The location of external foot markers and internal locations of the talonavicular and posterior subtalar joint were measured on each SWCT. Stepwise regression analysis was used to select the external markers that best predicted the three internal locations. RESULTS: Navicular heights measured on WBR and SWCT scans were not statistically different (p = .44), indicating that SWCTs recreate the weight-bearing position of the foot. The navicular tubercle and medial and lateral malleoli were the best predictors of subtalar and talonavicular joint locations. These palpable anatomical locations explained more variation in internal joint location (r2 > .79; SEE < 3.0 mm) than other landmarks. DISCUSSION: This study demonstrates that external palpable landmarks can predict the location of the talonavicular and subtalar joints.

The Relationship Between Angular Osteologic and Radiographic Measurements of the Human Talus and Calcaneus.

BACKGROUND: Radiographic imaging of the foot is commonly performed when medical evaluation is indicated. Angular measurements between bones may be assessed as part of the examination for trauma and foot biomechanics. However, angular relationships between surfaces of the physical bone as they compare with the bone's radiographic image has had limited investigation. METHODS: For this study, 54 human feet from amputated limbs were imaged in standard radiographic views and skeletonized. Selected angular measurements were taken on each skeletonized talus and calcaneus and were compared with those taken from radiographic images using paired Student t tests and linear regression analysis. RESULTS: Transverse plane measurements of the talus were not significantly different (P ≥ .05), associating strongly (r2 = 0.67-0.75; all P < .001). Most transverse and sagittal plane measurements of the calcaneus were not significantly different (P ≥ .05), with transverse plane measurements more strongly associated (r2 = 0.70-0.77; all P < .001) than sagittal plane measurements (r2 = 0.35-0.78; all P < .001). CONCLUSIONS: Selected angular measurements of the talus and calcaneus taken from radiographic images can be compared quantitatively with the physical bone, demonstrating that angular measurements from radiographic images provide useful information concerning both of these bones. This knowledge can be applied to the understanding of the morphology of the calcaneus and talus as it relates to human foot biomechanics and should also be of use in the interpretation of the human fossil pedal record.

Gastrocnemius or Achilles Lengthening at Time of Trauma Fixation.

Gastrocnemius equinus is a frequent comorbidity with traumatic injuries of the foot and ankle. Gastrocnemius lengthening at the time of definitive treatment facilitates obtaining and maintaining an anatomic reduction of the injury. The lengthening procedure is accomplished in 5 steps and results in fewer long-term, problematic sequelae.

Linear and angular measurements of the foot of modern humans: a test of Morton's foot types.

In his classic research, Morton established two functionally different configurations of the bipedal and non-bipedal primate foot: one optimized for stability, with a stiff longitudinal arch and adducted first metatarsal, and the other for compliance. Modern human feet were seen as conforming to the bipedal norm and variation from it as pathology, even though clinical evidence has been clear that variation from the norm of a stiff longitudinal arch or adducted first metatarsal exists. This study aims to document the variation in linear and angular measurements of the foot, using weight-bearing radiographs of 50 randomly selected people (25 men) from an urban US Level 1 trauma center. The radiographs were obtained to "rule-out" a foot fracture after trauma or as comparison films for a contralateral foot injury. Measurements were made using Osirix and correlations among the angular and length measurements were determined using Stata with P < 0.05 and Bonferroni correction for multiple comparisons. We found that foot length was not correlated with angular measurements, except for the angle between the first and fifth metatarsal. People with lower medial longitudinal arches also had more abducted first metatarsals and more vertical posterior facets, in accordance with Morton's foot types. Whether or not this variation in modern humans is linked to functionally important consequences remains to be determined in future research. With the new evidence of a more variable foot structure in fossil hominins, understanding the relationship between foot morphology and function becomes more urgent.

Plantar medial wounds associated with calcaneal fractures.

BACKGROUND: Calcaneal fractures with open wounds are prone to soft tissue complications. We describe a particular subclass of open injury that occurs on the plantar surface of the foot, medial to the anterior process of the calcaneus, the plantar medial wound (PMW). The purpose of this study was to evaluate soft tissue healing and potential complications in open calcaneal fractures that have a PMW. METHODS: We established the time to soft tissue healing and the status of the injured limb of 11 adults with 12 calcaneal fractures with a PMW. This was a retrospective review of prospectively gathered data at a Level I trauma center. RESULTS: Five fractures developed an infection requiring intravenous antibiotics. Two patients required split thickness skin grafts and 1 patient required a free gracilis flap 10 months after injury to treat a chronic open PMW with resolving osteomyelitis and required a below-knee amputation secondary to flap failure. The most commonly associated bony injury with a PMW was a transcalcaneal-talonavicular fracture dislocation (8/13 injuries). Nonunion of the calcaneal fracture occurred in 3 patients. CONCLUSION: Patients with this type of injury-even those with Gustilo Type I open fractures-need to be apprised that their injury is associated with long-term sequelae, including complications with wound healing, high infection rates, and a higher potential for subsequent amputation than other open hind foot wounds. The Tscherne classification of open wounds should be used in the future. LEVEL OF EVIDENCE: Level IV, retrospective case series.

Humans, geometric similarity and the Froude number: is ''reasonably close'' really close enough?

Understanding locomotor energetics is imperative, because energy expended during locomotion, a requisite feature of primate subsistence, is lost to reproduction. Although metabolic energy expenditure can only be measured in extant species, using the equations of motion to calculate mechanical energy expenditure offers unlimited opportunities to explore energy expenditure, particularly in extinct species on which empirical experimentation is impossible. Variability, either within or between groups, can manifest as changes in size and/or shape. Isometric scaling (or geometric similarity) requires that all dimensions change equally among all individuals, a condition that will not be met in naturally developing populations. The Froude number (Fr), with lower limb (or hindlimb) length as the characteristic length, has been used to compensate for differences in size, but does not account for differences in shape.To determine whether or not shape matters at the intraspecific level, we used a mechanical model that had properties that mimic human variation in shape. We varied crural index and limb segment circumferences (and consequently, mass and inertial parameters) among nine populations that included 19 individuals that were of different size. Our goal in the current work is to understand whether shape variation changes mechanical energy sufficiently enough to make shape a critical factor in mechanical and metabolic energy assessments.Our results reaffirm that size does not affect mass-specific mechanical cost of transport (Alexander and Jayes, 1983) among geometrically similar individuals walking at equal Fr. The known shape differences among modern humans, however, produce sufficiently large differences in internal and external work to account for much of the observed variation in metabolic energy expenditure, if mechanical energy is correlated with metabolic energy. Any species or other group that exhibits shape differences should be affected similarly to that which we establish for humans. Unfortunately, we currently do not have a simple method to control or adjust for size-shape differences in individuals that are not geometrically similar, although musculoskeletal modeling is a viable, and promising, alternative. In mouse-to-elephant comparisons, size differences could represent the largest source of morphological variation, and isometric scaling factors such as Fr can compensate for much of the variability. Within species, however, shape differences may dominate morphological variation and Fr is not designed to compensate for shape differences. In other words, those shape differences that are "reasonably close" at the mouse-to-elephant level may become grossly different for within-species energetic comparisons.

Brief communication: could Kadanuumuu (KSD-VP-1/1) and Lucy (AL 288-1) have walked together comfortably?

The estimated lower limb length (0.761-0.793 m) of the partial skeleton of Australopithecus afarensis from Woranso-Mille (KSD-VP-1/1) is outside the previously known range for Australopithecus and within the range of modern humans. The lower limb length of KSD-VP-1/1 is particularly intriguing when juxtaposed against the lower limb length estimate of the other partial skeleton of A. afarensis, AL 288-1 (0.525 m). A sample of 36 children (age, >7 years, trochanteric height = 0.56-0.765 m) and 16 adults (trochanteric height = 0.77-1.00 m) walked at their self-selected slow, preferred, and fast walking velocities, while their oxygen consumption was monitored. Lower limb length and velocity were correlated with slow (P < 0.001, r(2) = 0.44), preferred (P < 0.001, r(2) = 0.55), and fast (P < 0.001, r(2) = 0.69) walking velocity. The relationship between optimal velocity and lower limb length was also determined and lower limb length explained 47% of the variability in optimal velocity. The velocity profile for KSD-VP-1/1 (slow = 0.73-0.75 m/s, preferred = 1.08-1.11 m/s, and fast = 1.48-1.54 m/s) is 36-44% higher than that of AL 288-1 (slow = 0.53 m/s, preferred = 0.78 m/s, and fast = 1.07 m/s). The optimal velocity for AL 288-1 is 1.04 m/s, whereas that for KSD-VP-1/1 is 1.29-1.33 m/s. This degree of lower limb length dimorphism suggests that members of a group would have had to compromise their preferences to walk together or to split into subgroups to walk at their optimal velocity.

The effective mechanical advantage of a.L. 129-1a for knee extension.

The functional significance of shape differences between modern human and australopithecine distal femora remains unclear. Here, we examine the morphological component of the effective mechanical advantage (EMA) of the quadriceps muscle group in a sample of hominins that includes the fossil A.L. 129-1a (Australopithecus afarensis) and modern humans. Quadriceps muscle moment arms were calculated from three-dimensional computer models of specimens through a range of knee flexion. All hominins were compared using the same limb positions to allow us to examine, in isolation, the morphological component of the lengths of the pertinent moment arms. After taking into account the differences in bicondylar angle, the morphological component of the EMA was calculated as the ratio of the quadriceps muscle and ground reaction force moment arms. Our analyses reveal that A.L. 129-1a would have possessed a morphological component of the quadriceps muscle EMA expected for a hominin of its body mass.

The energetic cost of walking: a comparison of predictive methods.

BACKGROUND: The energy that animals devote to locomotion has been of intense interest to biologists for decades and two basic methodologies have emerged to predict locomotor energy expenditure: those based on metabolic and those based on mechanical energy. Metabolic energy approaches share the perspective that prediction of locomotor energy expenditure should be based on statistically significant proxies of metabolic function, while mechanical energy approaches, which derive from many different perspectives, focus on quantifying the energy of movement. Some controversy exists as to which mechanical perspective is "best", but from first principles all mechanical methods should be equivalent if the inputs to the simulation are of similar quality. Our goals in this paper are 1) to establish the degree to which the various methods of calculating mechanical energy are correlated, and 2) to investigate to what degree the prediction methods explain the variation in energy expenditure. METHODOLOGY/PRINCIPAL FINDINGS: We use modern humans as the model organism in this experiment because their data are readily attainable, but the methodology is appropriate for use in other species. Volumetric oxygen consumption and kinematic and kinetic data were collected on 8 adults while walking at their self-selected slow, normal and fast velocities. Using hierarchical statistical modeling via ordinary least squares and maximum likelihood techniques, the predictive ability of several metabolic and mechanical approaches were assessed. We found that all approaches are correlated and that the mechanical approaches explain similar amounts of the variation in metabolic energy expenditure. Most methods predict the variation within an individual well, but are poor at accounting for variation between individuals. CONCLUSION: Our results indicate that the choice of predictive method is dependent on the question(s) of interest and the data available for use as inputs. Although we used modern humans as our model organism, these results can be extended to other species.

The effect on energy expenditure of walking on gradients or carrying burdens.

The effectiveness of people walking while carrying burdens and/or on gradients has been of interest to anthropologists for some time. No empirical equation exists, however, to assess the energetic expenditure of individuals traveling downhill with burdens and whether or not all people increase their energetic expenditure over unburdened level travel when carrying relatively light burdens (<20% of body mass) remains unclear. To begin to rectify this lacunae, gait parameters, physiological variables, and the energetic expenditure of 11 adults were assessed as they walked with burdens of 5 and 10 kg on a level treadmill and while they walked unburdened on gradients +/-8 and +/-16%. These data were then compared to predictive equations and data available from the literature. Velocity and body mass were combined with gradient and burden mass, where appropriate, as independent covariates to create predictive equations, which explained >80% of the variation in energetic expenditure. These new equations are appropriate for predicting energetic expenditure in people carrying burdens of <20% of total body mass or walking up and downhill at gradients of <20%.