Surpassing Mt. Everest: extreme flight performance of alpine bumble-bees

Animal flight at altitude involves substantial aerodynamic and physiological challenges. Hovering at high elevations is particularly demanding from the dual perspectives of lift and power output; nevertheless, some volant insects reside and fly at elevations in excess of 4000 m. Here, we demonstrate that alpine bumble-bees possess substantial aerodynamic reserves, and can sustain hovering flight under hypobaria at effective elevations in excess of 9000 m, i.e. higher than Mt. Everest. Modulation of stroke amplitude and not wingbeat frequency is the primary means of compensation for overcoming the aerodynamic challenge. The presence of such excess capacity in a high-altitude bumble-bee is surprising and suggests intermittent behavioural demands for extreme flight performance supplemental to routine foraging.     

Development and validation of a computational model for understanding the effects of an upright birthing position on the female pelvis

Upright, natural birthing positions, such as squatting, are associated with several clinical benefits, yet recumbent positions are still most common during delivery in most health centres. The biomechanics of birth positioning are not yet fully understood; therefore, our objectives were to develop and validate a computational model that could determine pelvic kinematics under loading conditions resulting from an upright birthing position. A three-dimensional model of the pelvic region was created from MRI scans of a non-pregnant subject. Bones were designated rigid segments with sacroiliac and pubic symphysis joint motion constrained only by contact surfaces and ligaments modeled as non-linear spring elements. Actuating torques at the lumbosacral and hip joints were defined based on motion analyses of squatting. The model was validated by comparing simulation results with data from the literature and in vivo MRI data from three subjects in a kneel-squat position. Good agreement was found between clinical pelvimetry measurements from the squat simulation and MRI data. Differences between simulation predictions were within one standard deviation of mean MRI kneel-squat results for all clinical measurements except one: the predicted increase in bispinous diameter was approximately 1.5 standard deviations less than that of the mean MRI results and still well within physiologic limits according to data in the literature. This model can, therefore, be used to provide further insight into the biomechanics of certain upright birthing positions, such as squatting.     

Effects of flight behaviour on body temperature and kinematics during inter-male mate competition in the solitary desert bee Centris pallida

Abstract. Body temperatures and kinematics are measured for male Centris pallida bees engaged in a variety of flight behaviours (hovering, patrolling, pursuit) at a nest aggregation site in the Sonoran Desert. The aim of the study is to test for evidence of thermoregulatory variation in convective heat loss and metabolic heat production and to assess the mechanisms of acceleration and forward flight in field conditions. Patrolling males have slightly (1–3 °C) cooler body temperatures than hoverers, despite similar wingbeat frequencies and larger body masses, suggesting that convective heat loss is likely to be greater during patrolling flight than during hovering. Comparisons of thorax and head temperature as a function of air temperature (T_a) indicate that C. pallida males are thermoregulating the head by increasing heat transfer from the thorax to the head at cool T_a. During patrolling flight and hovering, wingbeat frequency significantly decreases as T_a increases, indicating that variation in metabolic heat production contributes to thermal stability during these behaviours, as has been previously demonstrated for this species during flight in a metabolic chamber. However, wingbeat frequency during brief (1–2 s) pursuits is significantly higher than during other flight behaviours and independent of T_a. Unlike most other hovering insects, C. pallida males hover with extremely inclined stroke plane angles and nearly horizontal body angles, suggesting that its ability to vary flight speed depends on changes in wingbeat frequency and other kinematic mechanisms that are not yet described.     

Motion Features of Legs in Volleyball Block Jump Based on Biomechanical Analysis

Blocking technology is one of the most important means to obtain score in volleyball, which has a great influence on the victory of the game. In this study, the vertical jump was analyzed to understand the movement characteristics of legs during training time. The kinematics and dynamics data of the legs of 10 volleyball players after training for 0 h, 0.5 h, 1 h and 2 h were studied by using an infrared light point motion capture system and force measuring platform. The results showed that the joint angles of the players who had 1 h and 2 h of training in the buffering and pedaling and stretching stages decreased markedly compared with those who had 0 h of training. The peak angular velocity and impulse of hip and knee joints after 1 h and 2 h of training decreased in the pedaling and stretching stage. In the flight stage, the time of flight and the height of center of gravity showed a downward trend, while the time of landing and the angle of the knee joint decreased. After 1 h and 2 h of training, at the moment of double-foot landing, the flexion and extension angle of the knee joint increased, and the angular velocity of the knee joint and ankle joint decreased markedly. The length of training time has a great impact on the joints of legs, including increasing joint pressure and the risk of injuries.     

Repeatability,reproducibility, and agreement of three computational methods to approximate the functional flexion-extension axis of the tibiofemoral joint using 3D bone models of the femur

Abstract

Background: Closely approximating the functional flexion-extension (FE) axis of the tibiofemoral joint in 3D models of the femur is important when computing joint motions which are physiologic. The objectives were to 1) develop methods to approximate the functional FE axis based on fitting circles, a tapered cylinder, and spheres to the posterior condyles, 2) determine the repeatability and reproducibility of each method, and 3) determine limits of agreement between pairs of axes.

Methods: For each method, the respective axis was determined in forty 3D bone models of the distal femur. Varus-valgus angles and internal-external axial angles were computed relative to standard planes.

Results: Repeatability and reproducibility were comparable for the tapered cylinder-based and sphere-based methods and better than that for the circle-based method. Limits of agreement were tightest when comparing the sphere-based and tapered cylinder-based axes. However, limits of agreement for the internal-external axial angle were wide at +3.6° to ?3.9° whereas limits of agreement were tighter at +1.4° to ?0.7° for the varus-valgus angle.

Conclusion: The tapered cylinder-based and sphere-based methods offer advantages of better repeatability and reproducibility over the circle-based method. However, the sphere-based and tapered cylinder-based axes are not interchangeable owing to wide limits of agreement for the internal-external axial angle. The tapered cylinder-based axis is preferred intuitively over the sphere-based axis because the spheres require fitting in both the sagittal and coronal planes whereas the tapered cylinder requires fitting in the sagittal plane only which is the plane of motion in flexion-extension.     

A joint coordinate system proposal for the study of the trapeziometacarpal joint kinematics

The International Society of Biomechanics (ISB) has recommended a standardisation for the motion reporting of almost all human joints. This study proposes an adaptation for the trapeziometacarpal joint.

The definition of the segment coordinate system of both trapezium and first metacarpal is based on functional anatomy. The definition of the joint coordinate system (JCS) is guided by the two degrees of freedom of the joint, i.e. flexion–extension about a trapezium axis and abduction–adduction about a first metacarpal axis. The rotations obtained using three methods are compared on the same data: the fixed axes sequence proposed by Cooney et al., the mobile axes sequence proposed by the ISB and our alternative mobile axes sequence. The rotation amplitudes show a difference of 9° in flexion–extension, 2° in abduction–adduction and 13° in internal–external rotation.

This study emphasizes the importance of adapting the JCS to the functional anatomy of each particular joint.     

A comparison of swimming structures and kinematics in three species of crustacean larvae

Crustacean larvae swim with paired rowing appendages that rotate around the body of the animal. The number of paired rowing appendages varies from one species of larvae to another. In addition, the size of the crustacean larvae is different between species and increases as they grow. The nature of the fluid forces changes as size increases, so the morphology and mechanics of swimming in these animals will change during increases in size. This article demonstrates the changing kinematics of locomotion between three species of crustacean larvae, which swim with one (Artemia franciscana), two (Carcinus maenas) or five (Homarus americanus) pairs of propulsive limbs. The relative change in the surface area and volume ratios of the locomotor structures are also demonstrated.     

Approximation of the functional kinematics of posterior stabilised total knee replacements using a two-dimensional sagittal plane patello-femoral model: comparing model approximation to in vivo measurement

Previous in vivo studies have observed that current designs of posterior stabilised (PS) total knee replacements (TKRs) may be ineffective in restoring normal kinematics in Late flexion. Computer-based models can prove a useful tool in improving PS knee replacement designs. This study investigates the accuracy of a two-dimensional (2D) sagittal plane model capable of predicting the functional sagittal plane kinematics of PS TKR implanted knees against direct in vivo measurement. Implant constraints are often used as determinants of anterior–posterior tibio-femoral positioning. This allowed the use of a patello-femoral modelling approach to determine the effect of implant constraints. The model was executed using motion simulation software which uses the constraint force algorithm to achieve a solution. A group of 10 patients implanted with Scorpio PS implants were recruited and underwent fluoroscopic imaging of their knees. The fluoroscopic images were used to determine relative implant orientation using a three-dimensional reconstruction method. The determined relative tibio-femoral orientations were then input to the model. The model calculated the patella tendon angles (PTAs) which were then compared with those measured from the in vivo fluoroscopic images. There were no significant differences between the measured and calculated PTAs. The average root mean square error between measured and modelled ranged from 1.17° to 2.10° over the flexion range. A sagittal plane patello-femoral model could conceivably be used to predict the functional 2D kinematics of an implanted knee joint. This may prove particularly useful in optimising PS designs.