Distance estimation in the third dimension in desert ants

Desert ants of the genus Cataglyphis perform large-scale foraging excursions from which they return to their nest by path integration. They do so by integrating courses steered and the distances travelled into a continually updated home vector. While it is known that the angular orientation is based on skylight cues, it still is largely enigmatic how the ants measure distances travelled. We extended the ants' task into the third dimension by training them to walk within an array of uphill and downhill channels, and later testing them on flat terrain, or vice versa. In these tests the ants indicated homing distances that did not correspond to the distances actually travelled, but to the ground distances; that is, to the sum of the horizontal projections of the uphill and downhill segments of the ants' paths. These results suggest a much more sophisticated mechanism of distance estimation than hitherto thought. The ants must be able to measure the slopes of undulating terrain and to integrate this information into their "odometer" for the distance estimation process.     

The influence of geographic variations on the muscular activity in selected sports movements

Surface EMG (SEMG) has been used frequently to study motion techniques or skills, body positions, material or equipment used, training-methodology and learning processes in sports and ergonomics. Little if any information is available on the effect of the geographical environment on the neuromuscular control of an athlete or workman during his/her performance or effort.

Motions were chosen in Alpine skiing and cycling.

Thirty-one certified ski instructors and twelve professional road cyclists participated in the study of geographical variance and its impact on muscle activity.

SEMG was measured from the agonists and antagonists of the upper- and lower limb. Skiers were measured on downhill slopes ranging from 19 to 51% while the cyclists performed with different saddle positions on 2, 7 and 12% slope inclinations, respectively.

Verification of the variation of muscular intensity (IEMG) over the slope inclination during a simulated giant slalom indicated that the muscular activity increased with increasing slope angle and decreased with decreasing slope angle, while heart rate measured with short-range radio telemetry increased at a constant rate between start and finish independent of the geographical variations.

In a direct descent on different slopes % levels the integrated EMG is well related to the inclination (r=0.82) confirming the findings of the giant slalom.

In cycling we found that, regardless of the pelvis position, the muscular intensity of lower limb muscles increased with increasing slope inclination, while the muscular intensity of the arms decreased with the same increasing slope inclination. In addition the decreased intensity of the arm muscles remained significantly higher with the pelvis (saddle) fully forward.

The geography of the terrain did influence the neuromuscular work and therewith probably the performance also. The influence however, varies with specific circumstances and is coupled with items of variability of the equipment used and the body regions involved.     

How gate setup and turn radii influence energy dissipation in slalom ski racing

This study examined whether gate setup and turn radii influence energy dissipation in slalom skiing. 3D kinematical measurements were performed over two runs on the same slope in a WC slalom competition with two different gate setups: 1) open gates (OG) and 2) open gates with a delayed gate (DG). Using the arithmetic mean of the skis' turn radii (R(AMS)) the slalom turns were divided into 1) initiation phase (R(AMS) > 15 m) and steering phase (R(AMS) < 15 m). The results show differences between OG and DG regarding: 1) the absolute center of gravity's (CG) velocity, 2) absolute acceleration, 3) CG turn radii and R(AMS), 4) ground reaction forces (F) and 5) energy dissipation during skiing (all p < .05). In both gate setups the highest F and the highest energy dissipation were present in the steering phase, whereas the correlation between R(AMS) and energy dissipation was low (OG: r = .364 and DG: r = .214, both p < .001). In summary, compared with plain open gates, an additional delayed gate prolonged the turn radii and decreased energy dissipation in the beginning of the initiation phase, despite the fact that the relative frequency of occurrence of the highest energy dissipation was higher in DG.     

Himalayan porter's specialization: metabolic power, economy, efficiency and skill

Carrying heavy loads in the Himalayan region is a real challenge. Porters face extreme ranges in terrain condition, path steepness, altitude hypoxia and climate for 6-8h a day, many months a year, since they were boys. It has been previously shown that, when carrying loads on level terrain, porters' metabolic economy is higher than in Caucasians but the reasons are still unknown. We monitored Nepalese porters both during 90 km trekking in Khumbu Valley and at two different altitudes (3490 and 5050 m above sea-level), where they were compared to Caucasian mountaineers during (22%) gradient walking. Both subject groups carried a load of up to 90% body mass. The remarkably higher performance of porters during uphill locomotion (+60% in speed, +39% mechanical power) is only partly explained by the lower cost of loaded walking (-20%), being also the result of a better cardio-circulatory adaptation to altitude, which generates a higher mass-specific metabolic power (+30%). Consequently, Nepalese porters show higher efficiency, both during uphill and downhill loaded walking. Their higher economy on steep paths cannot be ascribed to a better exchange between potential and kinetic energy, as in our experiments the body centre of mass travelled monotonically uphill (or downhill). A different oscillation pattern of the loaded head-trunk segment, together with the analysis of the different components of the mechanical work during load carrying, suggests that achieved motor skills in balancing the loaded body segment above the hip could play a role in determining the better economy of porters.     

Relative vs. absolute physiological measures as predictors of mountain bike cross-country race performance

The aims of this study were to document the effect terrain has on the physiological responses and work demands (power output) of riding a typical mountain bike cross-country course under race conditions. We were particularly interested in determining whether physiological measures relative to mass were better predictors of race performance than absolute measures. Eleven A-grade male cross-country mountain bike riders (VO2max 67.1 +/- 3.6 ml x kg(-1) x min(-1)) performed 2 tests: a laboratory-based maximum progressive exercise test, and a 15.5-km (six 2.58-km laps) mountain bike cross-country time trial. There were significant differences among the speed, cadence, and power output measured in each of 8 different terrain types found in the cross-country time trial course. The highest average speed was measured during the 10-15% downhill section (22.7 +/- 2.6 km x h(-1)), whereas the cadence was highest in the posttechnical flat sections (74.3 +/- 5.6 rpm) and lowest on the 15-20% downhill sections (6.4 +/- 12.1 rpm). The highest mean heart rate (HR) was obtained during the steepest (15-20% incline) section of the course (179 +/- 8 b x min(-1)), when the power output was greatest (419.8 +/- 39.7 W). However, HR remained elevated relative to power output in the downhill sections of the course. Physiological measures relative to total rider mass correlated more strongly to average course speed than did absolute measures (peak power relative to mass r = 0.93, p < 0.01, vs. peak power r = 0.64, p < 0.05; relative VO2max r = 0.80, p < 0.05, vs. VO2max r = 0.66, p < 0.05; power at anaerobic threshold relative to mass r = 0.78, p < 0.05, vs. power at anaerobic threshold r = 0.5, p < 0.05). This suggests that mountain bike cross-country training programs should focus upon improving relative physiological values rather than focusing upon maximizing absolute values to improve performance.     

Distance and non-randomness of seed dispersal by the dwarf cassowary Casuarius bennetti

To determine the sources of dispersed seeds I inserted unique tags in fallen Aglaia aff flavida seeds before dwarf cassowaries (Casuanus bennetti) ate the fruits containing the seeds Thirty naturally-dispersed, marked seeds were re-located in cassowary droppings m a 400 ha study area The distribution of seed dispersal distances did not differ significantly from a normal distribution with a mean dispersal distance of 388 m, SD= 196 8 Mean distance of dispersed seeds to nearest mature conspecific tree was 170 m, SD= 108 4, dispersed seeds usually landed closer to other conspecifics than their parent The estimated distribution of all seeds (including many undispersed seeds) was leptokurtic, creating high densities near source trees (>0 035 seeds m^-2 within 100 m of bole) that quickly tapered off (<0 002 seeds m^-2 > 100 m from the bole), any density dependent effects are liable to be manifest only near parent trees
Cassowary movement patterns and resting behavior caused non-random dispersal of seeds Seeds were preferentially moved to level sites uphill from their source trees along routes that did not cross.steep terrain Undispersed seeds generally landed downhill from source trees This population of Aglaia would probably contract downhill into smaller, fragmented populations m the absence of cassowary-mediated dispersal     

Migratory Orientation: Magnetic Compass Orientation of Garden Warblers (Sylvia borin) after a Simulated Crossing of the Magnetic Equator

Since the birds' magnetic compass works as an inclination compass using the axial course of the magnetic field lines and their inclination, transequatorial migrants have to reverse their reaction with respect to the magnetic field after crossing the magnetic equator. Garden Warblers, long distance migrants breeding in Europe and wintering in tropical and southern Africa, were tested during autumn in the local geomagnetic field on the northern hemisphere. The experimental group was exposed to a field with horizontal field lines, simulating equator crossing, at the beginning of October; afterwards the birds were tested in the local geomagnetic field again. While the controls showed southerly tendencies during the entire season, the experimentals reversed their directional tendencies after staying in the horizontal field and now preferred northerly directions. In a field of the southern hemisphere, this preference corresponds to a southern course which would have meant the continuation of their migration flight.     

Trekking poles increase physiological responses to hiking without increased perceived exertion

Trekking poles are used by hikers for improved stability and lowered leg fatigue due to increased upper body muscle involvement. However, the weight of the poles and exaggerated upper body movement when using poles may increase total energy expenditure at a given walking speed. Few studies have investigated the physiological responses of hiking with trekking poles outside the laboratory setting. The purposes of this study were to determine if trekking poles altered physiological responses to hiking on varied terrain, and whether responses between trials were dependent on the grade of the terrain. Fourteen recreational hikers completed four hiking trials over a course that included sustained sections of flat (0 +/- 1% grade), steep uphill (>10% grade), gradual uphill (5% grade), gradual downhill (-5% grade) and steep downhill (<-10% grade) terrain. Subjects walked at a self-selected speed that was matched across trials using time-splits and a metronome. Two trials were conducted with hiking poles and two without poles. [latin capital V with dot above]O2 was significantly elevated (p <0.05) during the pole trials (1502.9 +/- 510.7 ml/min) compared to the no-pole trials (1362.4 +/- 473.2 ml/min). Similarly, ventilatory efficiency ([latin capital V with dot above]E) (43.1 +/- 9.6; 38.3 +/- 10.1 L/min) and heart rate (HR) (112.1 +/- 9.7; 105.7 +/- 10.4 bt/min) were significantly higher during the pole trials than the no-pole trials. However, ratings of perceived exertion (RPE) was not altered by pole condition (8.5 +/- 0.7; 8.4 +/- 0.8). Comparisons within each grade revealed significantly higher physiological responses for [latin capital V with dot above]O2, [latin capital V with dot above]E and HR in the pole-condition at all grades, with no significant variable*grade interactions. RPE measures were not significantly different between pole trials at any grade. These data suggest that trekking poles may be a beneficial tool for increasing caloric expenditure, as energy production increased during exercise without increased perceptions of effort.     

How Do Ants Make Sense of Gravity? A Boltzmann Walker Analysis of Lasius niger Trajectories on Various Inclines

The goal of this study is to describe accurately how the directional information given by support inclinations affects the ant Lasius niger motion in terms of a behavioral decision. To this end, we have tracked the spontaneous motion of 345 ants walking on a 0.5×0.5 m plane canvas, which was tilted with 5 various inclinations by rad ( data points). At the population scale, support inclination favors dispersal along uphill and downhill directions. An ant''s decision making process is modeled using a version of the Boltzmann Walker model, which describes an ant''s random walk as a series of straight segments separated by reorientation events, and was extended to take directional influence into account. From the data segmented accordingly ( segments), this extension allows us to test separately how average speed, segments lengths and reorientation decisions are affected by support inclination and current walking direction of the ant. We found that support inclination had a major effect on average speed, which appeared approximately three times slower on the incline. However, we found no effect of the walking direction on speed. Contrastingly, we found that ants tend to walk longer in the same direction when they move uphill or downhill, and also that they preferentially adopt new uphill or downhill headings at turning points. We conclude that ants continuously adapt their decision making about where to go, and how long to persist in the same direction, depending on how they are aligned with the line of maximum declivity gradient. Hence, their behavioral decision process appears to combine klinokinesis with geomenotaxis. The extended Boltzmann Walker model parameterized by these effects gives a fair account of the directional dispersal of ants on inclines.     

Oxygen delivery does not limit peak running speed during incremental downhill running to exhaustion

Oxygen consumption (VO2), ventilation (VI), respiratory exchange ratio (R), stride frequency and blood lactate concentrations were measured continuously in nine trained athletes during two continuous incremental treadmill runs to exhaustion on gradients of either 0 degree or -3 degrees. Compared to the run at 0 degree gradient, the athletes reached significantly higher maximal treadmill velocities but significantly lower VO2, VI, R and peak blood lactate concentrations (P less than 0.001) during downhill running. These lower VO2 and blood lactate concentrations at exhaustion indicated that factors other than oxygen delivery limited maximal performance during the downhill run. In contrast, stride frequencies were similar at each treadmill velocity; the higher maximal speed during the downhill run was achieved with a significantly longer stride length (P less than 0.001); maximal stride frequency was the same between tests. Equivalent maximal stride frequencies suggested that factors determining the rate of lower limb stride recovery may have limited maximal running speed during downhill running and, possibly, also during horizontal running.     

无线电颈圈定位数据应用于卧龙大熊猫移动规律的研究

本文分析了1981 ～ 1983 年卧龙自然保护区6 只大熊猫的无线电定位数据,结合DEM 高程数据,应用地理信息系统(GIS)工具进行了大熊猫的垂直移动(海拔变化)和水平移动(2 个相邻日的移动距离变化)规律研究。应用了“箱图” 法和Mann-Whitney U test 统计检验方法进行分析比较。结果显示:卧龙地区的大熊猫从每年的4 月份起从2 800 m以上的高海拔区域下移至2 600 m左右的低海拔区域,在较低海拔生活至6 月底,然后上移回到2 800 m的高海拔区域,表明大熊猫存在“季节性垂直移动”。大熊猫的2 个相邻日移动距离年平均值为550 m;在4 月份的水平移动距离最大,达到700 多米,而在夏秋季的水平移动距离较小,为400 m上下。本研究中的雌雄体大熊猫在移动形式(海拔变化、相邻日移动距离变化) 上存在差异,雌体大熊猫下移海拔变化较雄体明显,但相邻日移动距离却明显比雄体小。本研究结果可为野外大熊猫监测和保护工作提供科学依据。     

Energetics and passive dynamics of the ankle in downhill walking

This study investigated the energetics of the human ankle during the stance phase of downhill walking with the goal of modeling ankle behavior with a passive spring and damper mechanism. Kinematic and kinetic data were collected on eight male participants while walking down a ramp with inclination varying from 0° to 8°. The ankle joint moment in the sagittal plane was calculated using inverse dynamics. Mechanical energy injected or dissipated at the ankle joint was computed by integrating the power across the duration of the stance phase. The net mechanical energy of the ankle was approximately zero for level walking and monotonically decreased (i.e., became increasingly negative) during downhill walking as the slope decreased. The indication is that the behavior of the ankle is energetically passive during downhill walking, playing a key role in dissipating energy from one step to the next. A passive mechanical model consisting of a pin joint coupled with a revolute spring and damper was fit to the ankle torque and its parameters were estimated for each downhill slope using linear regression. The passive model demonstrated good agreement with actual ankle dynamics as indicated by low root-mean-square error values. These results indicate the stance phase behavior of the human ankle during downhill walking may be effectively duplicated by a passive mechanism with appropriately selected spring and damping characteristics.     

Discrimination Contours for Moving Sounds Reveal Duration and Distance Cues Dominate Auditory Speed Perception

Evidence that the auditory system contains specialised motion detectors is mixed. Many psychophysical studies confound speed cues with distance and duration cues and present sound sources that do not appear to move in external space. Here we use the ‘discrimination contours’ technique to probe the probabilistic combination of speed, distance and duration for stimuli moving in a horizontal arc around the listener in virtual auditory space. The technique produces a set of motion discrimination thresholds that define a contour in the distance-duration plane for different combination of the three cues, based on a 3-interval oddity task. The orientation of the contour (typically elliptical in shape) reveals which cue or combination of cues dominates. If the auditory system contains specialised motion detectors, stimuli moving over different distances and durations but defining the same speed should be more difficult to discriminate. The resulting discrimination contours should therefore be oriented obliquely along iso-speed lines within the distance-duration plane. However, we found that over a wide range of speeds, distances and durations, the ellipses aligned with distance-duration axes and were stretched vertically, suggesting that listeners were most sensitive to duration. A second experiment showed that listeners were able to make speed judgements when distance and duration cues were degraded by noise, but that performance was worse. Our results therefore suggest that speed is not a primary cue to motion in the auditory system, but that listeners are able to use speed to make discrimination judgements when distance and duration cues are unreliable.     

Energy sources in alpine skiing (giant slalom)

The energy cost of a giant slalom event was measured in eight skiers of national level. The lap lasted on average 82 s. VO2 was measured during the first, the second and the last third of the lap in different trials and also during recovery from a complete lap. Blood lactate was measured at the end of a lap. From the data obtained it was possible to calculate that: a) VO2, as measured during the lap, would correspond at steady state to 80% of the VO2max of the subjects; b) the total metabolic power delivered during the lap should be equal to about 72 ml O2 X kg-1 X min-1, corresponding to 120% of VO2max of the subjects. Considering the short duration of the trial and the power output delivered during maximal efforts on a bicycle ergometer, it appears that the giant slalom is not a very high energy demanding event.     

Grip and limb force limits to turning performance in competition horses

Manoeuverability is a key requirement for successful terrestrial locomotion, especially on variable terrain, and is a deciding factor in predator-prey interaction. Compared with straight-line running, bend running requires additional leg force to generate centripetal acceleration. In humans, this results in a reduction in maximum speed during bend running and a published model assuming maximum limb force as a constraint accurately predicts how much a sprinter must slow down on a bend given his maximum straight-line speed. In contrast, greyhounds do not slow down or change stride parameters during bend running, which suggests that their limbs can apply the additional force for this manoeuvre. We collected horizontal speed and angular velocity of heading of horses while they turned in different scenarios during competitive polo and horse racing. The data were used to evaluate the limits of turning performance. During high-speed turns of large radius horizontal speed was lower on the bend, as would be predicted from a model assuming a limb force limit to running speed. During small radius turns the angular velocity of heading decreased with increasing speed in a manner consistent with the coefficient of friction of the hoof-surface interaction setting the limit to centripetal force to avoid slipping.     

Perceptual distance and the moon illusion

The elevated moon usually appears smaller than the horizon moon of equal angular size. This is the moon illusion. Distance cues may enable the perceptual system to place the horizon moon at an effectively greater distance than the elevated moon, thus making it appear as larger. This explanation is related to the size-distance invariance hypothesis. However, the larger horizon moon is usually judged as closer than the smaller zenith moon. A bias to expect an apparently large object to be closer than a smaller object may account for this conflict. We designed experiments to determine if unbiased sensitivity to illusory differences in the size and distance of the moon (as measured by d') is consistent with SDIH. A moon above a 'terrain' was compared in both distance and size to an infinitely distant moon in empty space (the reduction moon). At a short distance the terrain moon was adjudged as both closer and smaller than the reduction moon. But these differences could not be detected at somewhat greater distances. At still greater distances the terrain moon was perceived as both more distant and larger than the reduction moon. The distances at which these transitions occurred were essentially the same for both distance and size discrimination tasks, thus supporting SDIH.     

Variation of pelvic diameters due to different scanning positions--the experimental study

The distortion of human pelvis X ray scans, due to different scanning positions, can cause huge mistakes in estimation of pelvic diameters. The aim of the study was to quantify distortion of pelvic diameters in relation to scanning inclination angles. Twenty anatomically defined spots on the pelvis of a young male cadaver, freed of soft tissues, were marked with 3 mm metal balls. The digitalized X-ray scans were made with seven different but similar inclination angles, and marked spots were recognized by computer software. Obstetrical-gynecological (Ob-Gyn), horizontal and vertical diameters were measured between marked spots, and percentages of distortion were calculated for each new scanning position. Twenty seven distances on human pelvis from seven X-ray scans varied from -35.9% to 28.3%, on average 0.47%. This study has pointed to a high variation of vertical pelvic dimensions (4.94 +/- 5.73%), consequently making them unreliable in the estimation of general pelvic shape, and low variation of horizontal dimensions (0.92 +/- 0.61%). Generally, the percentage of variation of pelvic dimensions highly increases with inclination angle, in frontal and sagittal plane. Alteration of scanning distance by 4 cm has a weak influence on pelvic diameters. The most reliable Ob-Gyn pelvic diameter was conjugata diagonalis, then diameters obliqua prima and secunda, with an average length deviations of 3.4, 4.0, and 6.0% respectively. The conjugata anatomica was the most unreliable with an average variation of 11.5%.     

The effects of wind and posture on the aerodynamic performance during the flight stage of skiing

Numerical simulation is conducted to evaluate the wind and posture effects on the aerodynamic performance of a skier during the flight stage. Both steady and unsteady models are applied on a 2D geometry. Using the Fluent code, the fundamental equations of fluid flow are solved simultaneously. In particular we focus on the influence of wind speed and direction on aerodynamic forces with several different postures of the skier in steady modeling. For a chosen case, the unsteady models are used to predict the transient characteristics of streamline distributions and aerodynamic forces. It is found that the skier's postures, wind speed, and direction play a significant role. The wind condition affects the pressure force (the form drag) on the skier and makes it a resistance or thrust regarding wind directions. The optimized posture with a minimization of resistance under a facing wind is determined as a moving-forward body of the skier. The unsteady modeling reveals that the wake around the skier and aerodynamic forces are strongly dependent on time. This initial study not only provides a qualitative and theoretical basis for the athletes to understand the effects of wind and postures, and then to optimize their postures according to the wind condition during the flight stage of skiing, but also builds the foundation for the systematic study of skiing process with more advanced CFD models in the future.     

Quantification of water squirting by juvenile fluted giant clams (<Emphasis Type="Italic">Tridacna squamosa</Emphasis> L.)

The giant clam species Tridacna crocea, T. deresa, T. gigas, T. maxima and Hippopus hippopus are known to exhibit squirting behaviour, ejecting a stream of water either from their exhalant or inhalant siphon. Here, for the first time, squirting in juvenile fluted giant clams, T. squamosa, was measured. By analysing stills from video recordings it was possible to determine the horizontal and vertical distances travelled by each squirt above the water line, the cross-sectional area of the water jet, and the angle of squirt perpendicular to the horizontal axis of the giant clam. The weight of each “aerial squirt” was measured by collecting the displaced water. Using these parameters, the initial velocity, force and pressure exerted by each squirt on an object was calculated. Strong positive correlations were observed between shell length and weight of seawater and force exerted by aerial squirts. We also modelled the pressures that would be experienced by underwater targets. The simulated “underwater squirts” indicate the pressure produced rapidly decreases with distance from the clam.     

Combination of BMI and Waist Circumference for Identifying Cardiovascular Risk Factors in Whites

Objective: BMI (kilograms per meters squared) and waist circumference (WC) (measured in centimeters) are each associated with the risk of developing cardiovascular disease (CVD). Therefore, a combination of the two may be more effective in identifying subjects at risk than either alone. The present study sought to identify the combination of BMI and WC that has the strongest association with CVD risk factors in whites. Research Methods and Procedures: Subjects were 8712 white men and women from the Third National Health and Nutrition Examination Survey. The optimal combination of BMI and WC was developed using logistic regression models with BMI and WC as predictors and CVD risk factors as outcomes. The combined measure of BMI and WC using current cut‐off points was also examined. Sensitivity, specificity, and receiver operating characteristics curves were compared between the combined measures and BMI alone. Results: For white men, the optimal combination of BMI and WC for identifying CVD risk factors was 0.68 × BMI + 0.32 × WC. This combination generated a score that better estimated the odds of having CVD risk factors than either alone. For white women, WC alone largely determined the likelihood of having CVD risks. The combination of BMI and WC using current cut‐off points may provide an improved measure of CVD risk. Combined measures showed a higher sensitivity or a shorter distance in receiver operating characteristic curves in the identification of CVD risk factors. Discussion: Combined measures of BMI and WC may provide a higher overall test performance for CVD risk factors and may be useful in some ethnic groups as an improved means of screening subjects for further evaluation in the clinical setting.