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1.
In many sports, athletes perform motor tasks that simultaneously require both speed and accuracy for success, such as kicking a ball. Because of the biomechanical trade-off between speed and accuracy, athletes must balance these competing demands. Modelling the optimal compromise between speed and accuracy requires one to quantify how task speed affects the dispersion around a target, a level of experimental detail not previously addressed. Using soccer penalties as a system, we measured two-dimensional kicking error over a range of speeds, target heights, and kicking techniques. Twenty experienced soccer players executed a total of 8466 kicks at two targets (high and low). Players kicked with the side of their foot or the instep at ball speeds ranging from 40% to 100% of their maximum. The inaccuracy of kicks was measured in horizontal and vertical dimensions. For both horizontal and vertical inaccuracy, variance increased as a power function of speed, whose parameter values depended on the combination of kicking technique and target height. Kicking precision was greater when aiming at a low target compared to a high target. Side-foot kicks were more accurate than instep kicks. The centre of the dispersion of shots shifted as a function of speed. An analysis of the covariance between horizontal and vertical error revealed right-footed kickers tended to miss below and to the left of the target or above and to the right, while left-footed kickers tended along the reflected axis. Our analysis provides relationships needed to model the optimal strategy for penalty kickers.  相似文献   
2.
These experiments examined the changes in ventilation during a 40-s ramp increase in exercise load, produced by increasing either the speed of the treadmill or the grade, to equivalent end-points of oxygen uptake. Six subjects underwent five trials each for grade and speed, while ventilation was monitored breath-by-breath. For each subject, ventilation versus time for all five of the speed trials was plotted on a single graph and fitted by linear regression. The data for the grade trials were similarly treated. For all subjects, the slope of the regression line for the speed plots was found to be significantly (P < 0.05) greater than that for the grade plots. We concluded that these experimental results support the hypothesis that the neural drive to ventilation persists as exercise continues and is proportionately related to the frequency of limb movement.  相似文献   
3.
The present study investigated the feasibility and reliability of continuous relative phase (CRP) and deviation phase (DP) to assess intersegmental hind limb coordination pattern and coordination variability in rats during walking. Twenty-six adult rats walked at 8 m/min, 12 m/min and 16 m/min while two-dimensional kinematics were recorded. Segment angles and segment angular velocities of the paw, shank and thigh on the left hind-limb were extracted from 15 strides and CRP was calculated for the paw-shank and shank-thigh coupling. The effect of walking speed on the time point average curve of the CRP (ACRP) and DP and on the mean ACRP and mean DP was established by statistical parametric mapping (SPM) and a one-way ANOVA for repeated measures. Absolute and relative reliability were assessed by measurement error and intra-class correlation coefficient. The SPM analysis revealed time dependent differences in the effect of speed. Thus, the CRP of the paw-shank coupling decreased with increasing speed during most of the gait cycle while the CRP of the shank-thigh coupling was decreased during the swing phase. The session-to-session reliability was fair to good for the coordination measure and poor for the variability measure.  相似文献   
4.
AAA+ chaperone ClpX has been suggested to be a modulator of prokaryotic cytoskeletal protein FtsZ, but the details of recognition and remodeling of FtsZ by ClpX are largely unknown. In this study, we have extensively investigated the nature of FtsZ polymers and mechanisms of ClpX-regulated FtsZ polymer dynamics. We found that FtsZ polymerization is inhibited by ClpX in an ATP-independent manner and that the N-terminal domain of ClpX plays a crucial role for the inhibition of FtsZ polymerization. Single molecule analysis with high speed atomic force microscopy directly revealed that FtsZ polymer is in a dynamic equilibrium between polymerization and depolymerization on a time scale of several seconds. ClpX disassembles FtsZ polymers presumably by blocking reassembly of FtsZ. Furthermore, Escherichia coli cells overproducing ClpX and N-terminal domain of ClpX show filamentous morphology with abnormal localization of FtsZ. These data together suggest that ClpX modulates FtsZ polymer dynamics in an ATP-independent fashion, which is achieved by interaction between the N-terminal domain of ClpX and FtsZ monomers or oligomers.  相似文献   
5.
Synopsis Oxygen uptake (Vo 2) was measured in carp of approximately 40 cm length swimming at controlled variable oxygen tensions (Po 2). At Po 2> 120 mm Hg Vo 2 increased with an increase in swimming speed from 5.6 to 11.3 cm · sec–1. Extrapolation of Vo 2 to zero activity at Po 2 = 140 mm Hg revealed a standard O2 uptake of 36.7 ml O2 · kg–1 · h–1 at 20° C. At the lowest swimming speed (5.6 cm · s–1) the oxygen uptake increased when the water Po 2 was reduced. A near doubling in Vo 2 was seen at Po 2 = 70 mm Hg compared to 140 mm Hg. At higher swimming speeds in hypoxic water Vo 2 decreased relative to the values at low swimming speeds. As a result the slope of the lines expressing log Vo 2 as a function of swimming speed decreased from positive to negative values with decreasing Po 2 of the water. pH of blood from the caudal vein drawn before and at termination of swimming at Po 2 = 70 mm Hg and 100 mm Hg did not show any decrease in relation to rest values at Po 2 = 140 mm Hg. Blood lactate concentration did not increase during swimming at these tensions.  相似文献   
6.
It is well known that proprioception is composed of the senses of movement and position. Whereas tests of position sense are quite commonly used, tests of the acuity in perception of movement velocity are scarce. In the present study we examined some novel tests for assessing the sense of limb movement velocity, involving replication and discrimination of single-joint movement velocity. Specifically, we investigated: (1) whether replication of limb movement velocity is more accurate following active criterion movements as compared to passive; (2) whether antagonist muscle contraction during passive limb movement enhances velocity discrimination; (3) how criterion movement velocity influences response accuracy; (4) the relationship between movement velocity and movement extent during velocity replication; and (5) whether subjects really base discrimination of velocities on perceived velocity. Sixteen healthy subjects participated in four tests (I-IV). For each test, horizontal abductions were performed about the right glenohumeral joint from the sagittal plane. The subjects were required to actively replicate the velocity of either an active (Test I) or passive (Test II) criterion movement, or judge whether a passive/semipassive (passive during antagonist muscle contraction) movement was faster or slower than a previous passive/semipassive criterion movement (Test III/IV). The results revealed higher response accuracy for Test I compared to Test II and for slower movements compared to faster, but no difference in response accuracy between Test III and IV. For velocity discrimination, the analysis revealed that the subjects based their judgment on the difference between criterion and comparison velocity rather than time or extent cues.  相似文献   
7.
Trichoderma reesei cellobiohydrolase I (TrCel7A) is a molecular motor that directly hydrolyzes crystalline celluloses into water-soluble cellobioses. It has recently drawn attention as a tool that could be used to convert cellulosic materials into biofuel. However, detailed mechanisms of action, including elementary reaction steps such as binding, processive hydrolysis, and dissociation, have not been thoroughly explored because of the inherent challenges associated with monitoring reactions occurring at the solid/liquid interface. The crystalline cellulose Iα and IIII were previously reported as substrates with different crystalline forms and different susceptibilities to hydrolysis by TrCel7A. In this study, we observed that different susceptibilities of cellulose Iα and IIII are highly dependent on enzyme concentration, and at nanomolar enzyme concentration, TrCel7A shows similar rates of hydrolysis against cellulose Iα and IIII. Using single-molecule fluorescence microscopy and high speed atomic force microscopy, we also determined kinetic constants of the elementary reaction steps for TrCel7A against cellulose Iα and IIII. These measurements were performed at picomolar enzyme concentration in which density of TrCel7A on crystalline cellulose was very low. Under this condition, TrCel7A displayed similar binding and dissociation rate constants for cellulose Iα and IIII and similar fractions of productive binding on cellulose Iα and IIII. Furthermore, once productively bound, TrCel7A processively hydrolyzes and moves along cellulose Iα and IIII with similar translational rates. With structural models of cellulose Iα and IIII, we propose that different susceptibilities at high TrCel7A concentration arise from surface properties of substrate, including ratio of hydrophobic surface and number of available lanes.  相似文献   
8.
三叶半夏组培快繁与优良单株的选育   总被引:5,自引:1,他引:4  
本文利用组织培养技术实现了三种不同叶型三叶半夏的快速繁殖,并通过光合生理特征的比较对其优良单株进行了选育。结果表明:半夏能在分化培养基MS+6-BA 1.0 mg/L + NAA 0.2 mg/L+蔗糖3%+琼脂5.0 g/L和离体块茎诱导培养基(1/2 MS+IBA 0.03 mg/L+ NAA 0.01 mg/L+蔗糖5%+琼脂5.0 g/L+AC 0.3 g/L)上快速扩繁,继代繁殖系数为1:6.23,培养3个月后块茎的平均直径达0.88cm。 对其光合生理特征的研究结果表明:三叶半夏是一种典型的阴生植物,其光饱和点为700μmol·photons/s·m2;三种叶型的三叶半夏都存在着明显的光抑制现象,其中柳叶型最明显。本研究所选育的11个单株后代中,以桃叶2号(T2)的净光合速率和产量最高,柳叶2号(L2)对强光的耐受力最强。经过6个月的扩繁,本研究获得优良单株T2和L2离体块茎各1万颗。在温州乐清实验基地中经过1年的大田种植后得优良单株半夏块茎各100kg。  相似文献   
9.
It is becoming increasingly apparent that many pathogen populations, including those of insects, show high levels of genotypic variation. Baculoviruses are known to be highly variable, with isolates collected from the same species in different geographical locations frequently showing genetic variation and differences in their biology. More recent studies at smaller scales have also shown that virus DNA profiles from individual larvae can show polymorphisms within and between populations of the same species. Here, we investigate the genotypic and phenotypic variation of an insect baculovirus infection within a single insect host. Twenty four genotypically distinct nucleopolyhedrovirus (NPV) variants were isolated from an individual pine beauty moth, Panolis flammea, caterpillar by in vivo cloning techniques. No variant appeared to be dominant in the population. The PaflNPV variants have been mapped using three restriction endonucleases and shown to contain three hypervariable regions containing insertions of 70-750 bp. Comparison of seven of these variants in an alternative host, Mamestra brassicae, demonstrated that the variants differed significantly in both pathogenicity and speed of kill. The generation and maintenance of pathogen heterogeneity are discussed.  相似文献   
10.
The effects of temperature on aquatic and terrestrial locomotor performance, including measures of burst speed, endurance, and righting response, the inter-individual correlation between measures of locomotor performance, and the temporal repeatability of performance were assessed in juvenile western painted turtles, Chrysemys picta bellii. Locomotor performance increased as temperature increased, with Q 10 values ranging from 1.33 to 1.98 for burst speed and 2.28 to 2.76 for endurance measures. Righting response performance also increased with temperature. Aquatic and terrestrial measures of locomotor performance were highly correlated; however, righting response was not correlated with any other measure of performance. Measures of terrestrial locomotor performance were highly repeatable over the entire 30-week study period, whereas aquatic locomotor performance was only repeatable through week 12. The righting response was repeatable over a 6-week study period. Both the interindividual variation and temperature effects on locomotor performance likely influences the survival of turtles, especially juveniles, by affecting the length of time turtles are exposed to potential predators and their ability to escape.  相似文献   
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