Inferring muscle functional roles of the ostrich pelvic limb during walking and running using computer optimization

Owing to their cursorial background, ostriches (Struthio camelus) walk and run with high metabolic economy, can reach very fast running speeds and quickly execute cutting manoeuvres. These capabilities are believed to be a result of their ability to coordinate muscles to take advantage of specialized passive limb structures. This study aimed to infer the functional roles of ostrich pelvic limb muscles during gait. Existing gait data were combined with a newly developed musculoskeletal model to generate simulations of ostrich walking and running that predict muscle excitations, force and mechanical work. Consistent with previous avian electromyography studies, predicted excitation patterns showed that individual muscles tended to be excited primarily during only stance or swing. Work and force estimates show that ostrich gaits are partially hip-driven with the bi-articular hip–knee muscles driving stance mechanics. Conversely, the knee extensors acted as brakes, absorbing energy. The digital extensors generated large amounts of both negative and positive mechanical work, with increased magnitudes during running, providing further evidence that ostriches make extensive use of tendinous elastic energy storage to improve economy. The simulations also highlight the need to carefully consider non-muscular soft tissues that may play a role in ostrich gait

Musculoskeletal modelling of an ostrich (Struthio camelus) pelvic limb: influence of limb orientation on muscular capacity during locomotion

We developed a three-dimensional, biomechanical computer model of the 36 major pelvic limb muscle groups in an ostrich (Struthio camelus) to investigate muscle function in this, the largest of extant birds and model organism for many studies of locomotor mechanics, body size, anatomy and evolution. Combined with experimental data, we use this model to test two main hypotheses. We first query whether ostriches use limb orientations (joint angles) that optimize the moment-generating capacities of their muscles during walking or running. Next, we test whether ostriches use limb orientations at mid-stance that keep their extensor muscles near maximal, and flexor muscles near minimal, moment arms. Our two hypotheses relate to the control priorities that a large bipedal animal might evolve under biomechanical constraints to achieve more effective static weight support. We find that ostriches do not use limb orientations to optimize the moment-generating capacities or moment arms of their muscles. We infer that dynamic properties of muscles or tendons might be better candidates for locomotor optimization. Regardless, general principles explaining why species choose particular joint orientations during locomotion are lacking, raising the question of whether such general principles exist or if clades evolve different patterns (e.g., weighting of muscle force–length or force–velocity properties in selecting postures). This leaves theoretical studies of muscle moment arms estimated for extinct animals at an impasse until studies of extant taxa answer these questions. Finally, we compare our model’s results against those of two prior studies of ostrich limb muscle moment arms, finding general agreement for many muscles. Some flexor and extensor muscles exhibit self-stabilization patterns (posture-dependent switches between flexor/extensor action) that ostriches may use to coordinate their locomotion. However, some conspicuous areas of disagreement in our results illustrate some cautionary principles. Importantly, tendon-travel empirical measurements of muscle moment arms must be carefully designed to preserve 3D muscle geometry lest their accuracy suffer relative to that of anatomically realistic models. The dearth of accurate experimental measurements of 3D moment arms of muscles in birds leaves uncertainty regarding the relative accuracy of different modelling or experimental datasets such as in ostriches. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in ostriches for the first time, emphasizing that avian limb mechanics are highly three-dimensional and complex, and how no muscles act purely in the sagittal plane. A comparative synthesis of experiments and models such as ours could provide powerful synthesis into how anatomy, mechanics and control interact during locomotion and how these interactions evolve. Such a framework could remove obstacles impeding the analysis of muscle function in extinct taxa

Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds

How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width—the mediolateral (transverse) distance between successive footfalls—was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk–run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history

Do male and female trauma patients receive the same prehospital care? : An observational follow-up study

Background: Trauma-related mortality can be lowered by efficient prehospital care. Less is known about whether gender influences the prehospital trauma care provided. The aim of this study was to explore gender-related differences in prehospital trauma care of severely injured trauma patients, with a special focus on triage, transportation, and interventions. Methods: We performed a retrospective observational study based on local trauma registries and hospital and ambulance records in Stockholm County, Sweden. A total of 383 trauma patients (279 males and 104 females) > 15years of age with an Injury Severity Score (ISS) of > 15 transported to emergency care hospitals in the Stockholm area were included. Results: Male patients had a 2.75 higher odds ratio (95% CI, 1.2-6.2) for receiving the highest prehospital priority compared to females on controlling for injury mechanism and vital signs on scene. No significant difference between genders was detected regarding other aspects of the prehospital care provided. Conclusions: This study indicated that prehospital prioritization among severely injured late adolescent and adult trauma patients differs between genders. Knowledge of a more diffuse presentation of symptoms in female trauma patients despite severe injury may help to adapt and improve prehospital trauma care for this group.Peer reviewe

Adaptive Remodeling of Achilles Tendon: A Multi-scale Computational Model

While it is known that musculotendon units adapt to their load environments, there is only a limited understanding of tendon adaptation in vivo. Here we develop a computational model of tendon remodeling based on the premise that mechanical damage and tenocyte-mediated tendon damage and repair processes modify the distribution of its collagen fiber lengths. We explain how these processes enable the tendon to geometrically adapt to its load conditions. Based on known biological processes, mechanical and strain-dependent proteolytic fiber damage are incorporated into our tendon model. Using a stochastic model of fiber repair, it is assumed that mechanically damaged fibers are repaired longer, whereas proteolytically damaged fibers are repaired shorter, relative to their pre-damage length. To study adaptation of tendon properties to applied load, our model musculotendon unit is a simplified three-component Hill-type model of the human Achilles-soleus unit. Our model results demonstrate that the geometric equilibrium state of the Achilles tendon can coincide with minimization of the total metabolic cost of muscle activation. The proposed tendon model independently predicts rates of collagen fiber turnover that are in general agreement with in vivo experimental measurements. While the computational model here only represents a first step in a new approach to understanding the complex process of tendon remodeling in vivo, given these findings, it appears likely that the proposed framework may itself provide a useful theoretical foundation for developing valuable qualitative and quantitative insights into tendon physiology and pathology

Security lies in obedience - Voices of young women of a slum in Pakistan

<p>Abstract</p> <p>Background</p> <p>Existing literature shows that young people, especially women, have poor knowledge about sexuality and reproductive health. Many of the difficulties young women experience are related to beliefs and expectations in society making them more vulnerable to reproductive ill health. The objective of this study was to explore how young women living in a slum in Islamabad are prepared for marriage and how they understand and perceive their transition to marriage and the start of sexual and childbearing activity.</p> <p>Methods</p> <p>Twenty qualitative interviews and three focus group discussions were conducted with young women residing in a slum of Islamabad. Content analysis was used to explore how the participants represented and explained their situation and how decisions about their marriage were made.</p> <p>Results</p> <p>The main theme identified was <it>security lies in obedience</it>. The two sub-themes contributing to the main theme were <it>socialization into submissiveness </it>and <it>transition into adulthood in silence</it>. The theme and the sub-themes illustrate the situation of young women in a poor setting in Pakistan.</p> <p>Conclusion</p> <p>The study demonstrates how, in a culture of silence around sexuality, young women's socialization into submissiveness lays the foundation for the lack of control over the future reproductive health that they experience.</p

Is 'Opt-Out HIV Testing' a real option among pregnant women in rural districts in Kenya?

PMTCT allows people living with HIV to actualize childbearing. However, it also complicates motherhood, as the medical consequences and public health implications of non-adherence to PMTCT service recommendations disrupt socio-cultural expectations of childbearing and parenthood. This thesis aimed to study childbearing and adherence to PMTCT interventions focusing on how women living with HIV realize motherhood in Kenya. We sought to answer how women on ART experience motherhood and how motherhood aggravate adherence to PMTCT services Methods: A quantitative cross sectional study (I) with a questionnaire survey conducted among pregnant women at their first visit to antenatal clinic to study consent to HIV testing and three qualitative studies analyzed with content analysis (II and IV) and narrative structuring (III) were included. Qualitative interviews were performed with women living with HIV who were pregnant, recently delivered and those actively planning a pregnancy to explore views and experiences when seeking a pregnancy (II), the reasoning and deciding about adherence to PMTCT (III) and how motherhood interferes with HIV treatment (IV). Results: ‘Striving for motherhood’ was the overriding theme describing the desire of women on ART to be parents while negotiating the challenges of living with HIV (IIV). Children improve women’s position in society and are a sign of a happy and fulfilled life (II-IV). Of 900 pregnant women surveyed at their first visit to antenatal care clinic, only 17% understood that HIV testing is optional (I). Making an informed decision to decline HIV testing was associated with knowing that testing was optional (OR=5.44, 95%CI 3.44-8.59), not having a stable relationship with the child’s father (OR=1.76, 95%CI 1.02-3.03), and not having discussed HIV testing with a partner before the ANC visit (OR=2.64 95%CI 1.79-3.86). Socio-economic affluence and residence influence behaviors such as no condom use, non-disclosure of HIV infection, use of traditional medicine simultaneously with ART, home delivery and stigma and discrimination from partners, family and community, all of which undermine adherence to PMTCT services (II-IV). Structural shortcomings in PMTCT result in the lack of antiretroviral HIV medicines, practice of mixed infant feeding and missed appointments (I, III, IV). Conclusion: Motherhood is achieved at the cost of striving to balance socio-cultural expectations of childbearing that also conceals their HIV infection at the cost of nonadherence to PMTCT recommendations. Being infected with HIV does not remove the desire of motherhood and related socio-cultural demands. It is important to acknowledge the significance childbearing among women infected with HIV to improve adherence. Women with chronic illness such as HIV-infection who are dependent on continuous medication and health check-ups struggle to balance the desire for children with the needs related to their illness and the expectations of being a ‘good mother’

The influence of speed and size on avian terrestrial locomotor biomechanics: predicting locomotion in extinct theropod dinosaurs

How extinct, non-avian theropod dinosaurs moved is a subject of considerable interest and controversy. A better understanding of non-avian theropod locomotion can be achieved by better understanding terrestrial locomotor biomechanics in their modern descendants, birds. Despite much research on the subject, avian terrestrial locomotion remains little explored in regards to how kinematic and kinetic factors vary together with speed and body size. Here, terrestrial locomotion was investigated in twelve species of ground-dwelling bird, spanning a 1,780-fold range in body mass, across almost their entire speed range. Particular attention was devoted to the ground reaction force (GRF), the force that the feet exert upon the ground. Comparable data for the only other extant obligate, striding biped, humans, were also collected and studied. In birds, all kinematic and kinetic parameters examined changed continuously with increasing speed, while in humans all but one of those same parameters changed abruptly at the walk-run transition. This result supports previous studies that show birds to have a highly continuous locomotor repertoire compared to humans, where discrete ‘walking’ and ‘running’ gaits are not easily distinguished based on kinematic patterns alone. The influences of speed and body size on kinematic and kinetic factors in birds are developed into a set of predictive relationships that may be applied to extinct, non-avian theropods. The resulting predictive model is able to explain 79–93% of the observed variation in kinematics and 69–83% of the observed variation in GRFs, and also performs well in extrapolation tests. However, this study also found that the location of the whole-body centre of mass may exert an important influence on the nature of the GRF, and hence some caution is warranted, in lieu of further investigation