Body movements during the off-ice execution of back spins in figure skating

Using an optoelectronic motion capture system, we quantitatively assessed the arrangement of body segments and the displacement of the horizontal projection of the center of mass (CM) in seven skaters performing off-ice back spins on a rotating device (spinner). The position of the CM at the beginning of the spins was not a determining factor, but its rapid stabilization towards the center of the spinner, together with the achievement of a stable arrangement of trunk and limbs, was crucial to get the dynamic equilibrium, necessary for a lasting performance. At full spinning, however, there was an indicative variety of individual body postures. A final deceleration, associable with the loss of body equilibrium, was detected in the last spin of most of skaters.In conclusion, the current investigation demonstrated that the off-ice execution of back spin, a critical movement of ice skating, can be measured in laboratory, thus providing quantitative information to both the skaters and the coaches. The analysis is not invasive, and it may be proposed also for longitudinal evaluations of skating and postural training.     

Binding Sites of the Polyamines Putrescine,Cadaverine, Spermidine and Spermine on A- and B-DNA Located by Simulated Annealing

Abstract

Molecular dynamics simulations with simulated annealing are performed on polyamine-DNA systems in order to determine the binding sites of putrescine, cadaverine, spermidine and spermine on A- and B-DNA. The simulations either contain no additional counterions or sufficient Na⁺ ions, together with the charge on the polyamine, to provide 73% neutralisation of the charges on the DNA phosphates. The stabilisation energies of the complexes indicate that all four polyamines should stabilise A-DNA in preference to B-DNA, which is in agreement with experiment in the case of spermine and spermidine, but not in the case of putrescine or cadaverine. The major groove is the preferred binding site on A-DNA of all the polyamines. Putrescine and cadaverine tend to bind to the sugar-phosphate backbone of B-DNA, whereas spermidine and spermine occupy more varied sites, including binding along the backbone and bridging both the major and minor grooves.     

Neuromuscular performance of Bandal Chagui: Comparison of subelite and elite taekwondo athletes

With the aim of comparing kinematic and neuromuscular parameters of Bandal Chagui kicks between 7 elite and 7 subelite taekwondo athletes, nine Bandal Chaguis were performed at maximal effort in a selective reaction time design, simulating the frequency of kicks observed in taekwondo competitions. Linear and angular leg velocities were recorded through 3D motion capture system. Ground reaction forces (GRF) were evaluated by a force platform, and surface electromyographic (sEMG) signals were evaluated in the vastus lateralis, biceps femoris, rectus femoris, tensor fasciae lata, adductor magnus, gluteus maximus, gluteus medius, and gastrocnemius lateralis muscles of the kicking leg. sEMG data were processed to obtain the cocontraction indices (CI) of antagonist vs. overall (agonist and antagonist) muscle activity. CI was measured for the hip and knee, in flexion and extension, and for hip abduction. Premotor, reaction (kinetic and kinematic), and kicking times were evaluated. Timing parameters, except kinetic reaction time, were faster in elite athletes. Furthermore, CI and angular velocity during knee extension, foot and knee linear velocity, and horizontal GRF were significantly higher in elite than in subelite athletes. In conclusion, selected biomechanical parameters of Bandal Chagui appear to be useful in controlling the training status of the kick and in orienting the training goal of black belt competitors.     

Lower-limb muscle function during sidestep cutting

To investigate lower-limb muscle function during sidestep cutting, prior studies have analysed electromyography (EMG) data together with three dimensional motion analysis. Such an approach does not directly quantify the biomechanical role of individual lower-limb muscles during a sidestep cut. This study recorded three dimensional motion analysis, ground reaction force (GRF) and EMG data for eight healthy males executing an unanticipated sidestep cut. Using a musculoskeletal modelling approach, muscle function was determined by computing the muscle contributions to the GRFs and lower-limb joint moments. We found that bodyweight support (vertical GRF) was primarily provided by the vasti, gluteus maximus, soleus and gastrocnemius. These same muscles, along with the hamstrings, were also primarily responsible for modulating braking and propulsion (anteroposterior GRF). The vasti, gluteus maximus and gluteus medius were the key muscles for accelerating the centre-of-mass towards the desired cutting direction by generating a medially-directed GRF. Our findings have implications for designing retraining programs to improve sidestep cutting technique.     

Influence of IMU position and orientation placement errors on ground reaction force estimation

Wearable inertial measurement units (IMU) have been proposed to estimate GRF outside of specialized laboratories, however the precise influence of sensor placement error on accuracy is unknown. We investigated the influence of IMU position and orientation placement errors on GRF estimation accuracy. Methods: Kinematic data from twelve healthy subjects based on marker trajectories were used to simulate 1848 combinations of sensor position placement errors (range ± 100 mm) and orientation placement errors (range ± 25°) across eight body segments (trunk, pelvis, left/right thighs, left/right shanks, and left/right feet) during normal walking trials for baseline cases when a single sensor was misplaced and for the extreme cases when all sensors were simultaneously misplaced. Three machine learning algorithms were used to estimate GRF for each placement error condition and compared with the no placement error condition to evaluate performance. Results: Position placement errors for a single misplaced IMU reduced vertical GRF (VGRF), medio-lateral GRF (MLGRF), and anterior-posterior GRF (APGRF) estimation accuracy by up to 1.1%, 2.0%, and 0.9%, respectively and for all eight simultaneously misplaced IMUs by up to 4.9%, 6.0%, and 4.3%, respectively. Orientation placement errors for a single misplaced IMU reduced VGRF, MLGRF, and APGRF estimation accuracy by up to 4.8%, 7.3%, and 1.5%, respectively and for all eight simultaneously misplaced IMUs by up to 20.8%, 23.4%, and 12.3%, respectively. Conclusion: IMU sensor misplacement, particularly orientation placement errors, can significantly reduce GRF estimation accuracy and thus measures should be taken to account for placement errors in implementations of GRF estimation via wearable IMUs.     

Optimal shear cushion stiffness at different gait speeds

The present study quantified the effects of different shear cushion stiffness on the time to peak posterior shear force (TPPSF), peak posterior shear force (PPSF), average posterior loading rate (APLR), and maximum posterior loading rate (MPLR) at different locomotion speeds using a custom-made sliding platform, as well as to identify the optimal stiffness of shear cushion. Twelve male collegiate students (heel-strikers) performed walking at 1.5 m/s, jogging at 2.5 m/s, and running at 3.5 m/s. A custom-made sliding platform was used to provide the different shear cushion conditions. The shear cushion conditions were fixed (a fixed platform; control group), stiff (K = 2746 N/m), medium stiff (K = 2256 N/m), medium soft (K = 1667 N/m), and soft (K = 1079 N/m). The results showed that all cushion conditions produced sliding displacement and delayed the TPPSF during walking, jogging, and running compared with fixed condition. The APLR and MPLR were lowest under medium soft condition during walking, while the PPSF was similar between medium soft and soft conditions. For jogging and running, the PPSF as well as APLR and MPLR were the lowest under medium stiff condition except the maximum PLR was similar among stiff, medium stiff, and medium soft conditions during running. In conclusion, shear cushion produces appropriate sliding displacement and effectively delays the TPPSF to provide the musculoskeletal system additional time to absorb the impact and reduce loading. The present study demonstrates optimal stiffness of shear cushion at different traveling speeds and suggests that a shear cushion system can be applied in future designs of cushion structures.     

The use of ground beetles (Coleoptera: Carabidae) in conservation assessments of exposed riverine sediment habitats in Scotland and northern England

Exposed riverine sediments (ERS) are an important invertebrate habitat. Ground beetle data from pitfall trap surveys of 165 sites in the catchments of the Rivers Carron, Nith, Spey, Tweed and Eden and from 48 sites in the catchments of the Rivers Blyth, Breamish, Coquet, Glen, Pont, South Tyne, Till, Tweed and Tyne were used to produce ERS habitat classifications in Scotland and northern England respectively. Within each habitat type the quality of sites were assessed using indices based on rarity and fidelity values and using species richness as a measure of diversity. Considerable variation in these indices was seen within and between habitat types, showing potential for their use in assessing site quality and for ranking sites within habitats. The use of standardised invertebrate survey and distribution data, together with species assemblage information, for the conservation of invertebrate habitat types as an alternative to the use of selected indicator species, is discussed.     

Alien plant species composition and associations with anthropogenic disturbance in North American forests

A probability-based sampling scheme was used to survey plant species composition in forests of 16 states in seven geopolitical regions of the United States (California, Colorado, Minnesota, and parts of the Pacific Northwest, Southeast, Mid-Atlantic, and Northeast) in 1994. The proportion of alien species relative to the total species number and to canopy cover in the ground stratum (0–0.6 m height) was evaluated in 279 plots. Visually evident anthropogenic disturbances (e.g., artificial regeneration, logging, prescribed burning, and grazing by livestock), if any, were recorded on each plot. In each of the seven regions we quantified (1) the percentage of the number of species and total cover comprised of alien species, (2) the difference in these percentages for disturbed and undisturbed plots, and (3) the origin or native range for the alien species.The percentage of alien species ranged from approximately 4.5% (Colorado) to approximately 13.2% (California). The percentage of alien species cover ranged from approximately 1.5% in Colorado to 25% in California. In five regions, species introduced from temperate Eurasia comprised the largest proportion of alien species and cover. In the Southeast, species introduced from far eastern and subtropical Asia dominated the alien flora. In the Mid-Atlantic, the majority of alien species was Eurasian and the majority of alien species cover consisted of far eastern and subtropical Asian species.The proportion of plots in which at least one alien species was recorded was significantly higher in disturbed than undisturbed plots in the Southeast and marginally significantly higher ($p=0.053$) in the Northeast. These results are consistent with other published studies that indicate that anthropogenic disturbance affects the structure and composition of both the ground stratum and upper canopy of forest habitats. In other regions, however, no significant differences were found.     

神经网络提高肝细胞癌磁共振波谱诊断正确率

通过评价31磷磁共振波谱(31Phosphorus Magnetic Resonance Spectroscopy,31P-MRS)来辨别三种诊断类型:肝细胞癌,正常肝和肝硬化。运用反向传输神经网络(BP)和径向基函数神经网络(RBF)分析31P-MRS数据,分别建立神经网络模型,进行肝细胞癌的诊断分类以期提高识别率。实验结果证明,应用神经网络模型后,31P-MR波谱对活体肝细胞癌的诊断正确率从89.47%提高到97.3%,且BP更优于RBF。     

Electrophysiological identification of the sugar cell in antennal taste sensilla of the predatory ground beetle Pterostichus aethiops

By single sensillum tip recording technique, in addition to the salt and pH cells found in antennal taste sensilla of some ground beetles earlier, the third chemosensory cell of four innervating these large sensilla was electrophysiologically identified as a sugar cell in the ground beetle Pterostichus aethiops. This cell generated action potentials of considerably smaller amplitude than those of the salt and pH cells, and phasic-tonically responded to sucrose and glucose over the range of 1-1000 mM tested. Responses were concentration dependent, with sucrose generating more spikes than glucose. During the first second of the response, maximum rates of firing of the sugar cell reached up to 19 and 37 imp/s when stimulated with 1000 mM glucose and sucrose, respectively. Three to four seconds later, the responses decreased close to zero. Both sugars are important in plant carbohydrate metabolism. These ground dwelling insects may come into contact with live and decayed plant material everywhere in their habitat including their preferred overwintering sites in brown-rot decayed wood. In conclusion, we hypothesize that high content of soluble sugars in their overwintering sites and refugia is unfavourable for these ground beetles, most probably to avoid contact with dangerous fungi.