The pattern of hammer speed during a hammer throw and influence of gravity on its fluctuations

Hammer speed at release is one of the most important factors contributing to the distance of a hammer throw. Hammer speed follows a generally increasing trend during the throw, with one fluctuation per turn. The purpose of the present paper was to quantify the influence of gravity on the speed fluctuations. Eight experienced hammer throwers were studied with three-dimensional filming methods. Instantaneous values of hammer velocity and speed were calculated from the film data. The rate of change of hammer speed due to the tangential component of gravity was computed, and integrated to calculate the accumulated contribution of gravity to hammer speed at all instants of the throw. These values were subtracted from the corresponding values of hammer speed. The amplitude of the fluctuations was reduced in the corrected speed functions, indicating a contribution of gravity to the original fluctuations. However, the fluctuations were still clearly present in the corrected speed functions, indicating the existence of other causal factors.     

Influence of contraction force and speed on muscle fiber conduction velocity during dynamic voluntary exercise.

Before using electromyographic (EMG) variables such as muscle fiber conduction velocity (MFCV) and the mean or median frequency (MDF) of an EMG power spectrum as indicators of muscular fatigue during dynamic exercises, it is necessary to determine the influence of a joint angle, contraction force and contraction speed on the EMG variables. If these factors affect the EMG variables, their influence must be removed or compensated for before discussing fatigue. The vastus lateralis of eight normal healthy male adults was studied. EMG signals during non-fatiguing dynamic knee extension exercises were detected with a three-bar active surface electrode array. EMG variables were calculated from the detected signals and compared with the angle of the knee joint, the extension torque and the extension speed. The extension torque was set at four levels with 10% intervals between 40 and 70% of the maximum voluntary contraction. The extension speed was set at five levels with 60 degrees /s intervals between 0 and 240 degrees /s. Because the joint angle unsystematically affected the MFCV, EMG variables at a given joint angle were extracted for comparison. The influence of the extension torque and speed on the extracted EMG variables was clarified with an ANOVA and a regression analysis. The statistical analyses showed that MFCV increased with the extension torque but did not depend on the extension speed. In contrast, MDF was independent of the extension torque but was dependent on the extension speed. MDF thus showed a behavior different from that of MFCV. It became clear that if MFCV is used as an indicator of muscular fatigue during dynamic exercises, it is at least necessary to extract MFCV at a predetermined joint angle and then remove the influence of extension torque on MFCV.     

Effects of speed and distance of muscle shortening on force depression during voluntary contractions

The purpose of this study was to determine the influence of speed and distance of muscle shortening on the amount of force depression for voluntary contractions. Two experimental tests were performed. In the first test, subjects performed isometric knee extensor contractions following muscle shortening produced by isokinetic knee extensions over the range 25-50 degrees. In the second test, subjects performed isometric knee extensor contractions following muscle shortening produced by isokinetic knee extensions at two speeds: 20 and 240 degrees /s. Knee extensor moments, surface electromyographical (EMG) signals of quadriceps femoris, and interpolated twitch moments were measured during all contractions and were compared with the corresponding values obtained during purely isometric contractions. Force depression following muscle shortening for the voluntary contractions tested in this study did not depend on the distance or the speed of muscle shortening. These results are in contrast to the corresponding results in the literature obtained using artificial electrical stimulation in which force depression was always found to be directly related to the distance of shortening and inversely related to the speed of shortening. The difference in force depression as a function of the distance and speed of muscle shortening between voluntary and artificial electrical stimulation may be associated with changes in activation following the voluntary shortening contractions, whereas activation is controlled and constant in all artificial stimulation protocols.     

Flight speed of seabirds in relation to wind speed and direction

We studied flight speed among all major seabird taxa. Our objectives were to provide further insight into dynamics of seabird flight and to develop allometric equations relating ground speed to wind speed and direction for use in adjusting seabird density estimates (calculated from surveys at sea) for the effect of bird movement. We used triangulation at sea to estimate ground speeds of 1562 individuals of 98 species. Species sorted into 25 “groups” based on similarity in ground speeds and taxonomy. After they were controlled for differences inground speed, the 25 groups sorted into eight major “types” on the basis of response to wind speed and wind direction. Wind speed and direction explained 1664% of the variation in ground speed among seabird types. For analyses on air speed (ground speed minus apparent wind speed), we divided the 25 groups according to four flight styles: gliding, flap-gliding, glide-flapping and flapping. Tailwind speed had little effect on air speed of gliders (albatrosses and large gadfly petrels), but species that more often used flapping decreased air speed with increase in tailwinds. All species increased air speeds significantly with increased headwinds. Gliders showed the greatest increase relative to increase in headwind speed and flappers the least. With tailwind flight, air speeds were greatest among species with highest wing loading for each flight style except gliders, which showed no relationship. For headwind flight, species with higher wing loading had higher air speeds; however, the relation was weaker in flappers compared with species using some amount of gliding. In contrast, analyses for air speed ratio (i.e. difference between air speed in acrosswinds [with no apparent wind] and speed flown into headwinds, or with tailwinds, divided by speed acrosswind) revealed that among species using some flapping, and with lower wing loading (surface-feeding shearwaters, small gadfly petrels, storm petrels, phalaropes, gulls and terns), adjusted air speeds more than those with higher wing loading (alcids, “diving shearwaters”, “Manx-type shearwaters”, pelicans, boobies and cormorants). As a result, most flappers of low wing loading flew much faster than V_mr (the most energy efficient air speed per distance flown) when flying into headwinds. We suggest that better-than-predicted gliding performance with acrosswinds and tailwinds of large gadfly petrels, compared with albatrosses, resulted from a different type of “soaring” not previously described in seabirds.     

The effect of wind speed and direction on the distribution of sewage-associated bacteria

A study of the relationship between wind and the distribution of sewage-associated bacteria was undertaken at a location where the sewage was discharged into the sea adjacent to the mouth of a river. The numbers of presumptive Escherichia coli were determined in 149 sea-water samples taken from three locations at distances of 1.9, 2.4 and 4.3 km from the outfall. On each sampling occasion, data on the wind speed and direction in the 3 h prior to collection of the samples were also collected. Analysis of these data demonstrated a significant role for wind speed and direction. With respect to wind direction, the numbers of presumptive E. coli present in a sample were significantly higher when the sample site lay downwind of the outfall. Wind speed was shown to have an influence on the numbers of presumptive E. coli only when the sample site was downwind of the outfall. In an analysis of 61 samples, an inverse correlation (r2 = 0.73) between salinity and log presumptive E. coli numbers was demonstrated. These data demonstrate that wind speed and direction at the time of sampling significantly influence the numbers of presumptive E. coli detected in any sea-water sample. It is argued that failure to pay sufficient attention to these parameters in the design of monitoring programmes may result in the generation of data that could provide a seriously distorted picture of the microbiological status of a water body.     

Local effects of wind speed and direction on the phytoplankton of the Southern Bight

The causes of the exceptionally early blooms of Ceratium spp.in the Southern Bight of the North Sea during the early 1970sare re-assessed. This localised event is found to coincide witha change in the meridional circulation over the North Sea inthe late winter and early spring, with abnormally strong northerliesduring the 1960s giving way to strengthened southerlies duringthe early 1970s. Such a change in wind direction can be expected(both from observation and simulation) to bring about a lesswidespread distribution of turbid coastal water in the SouthernBight and the marked reduction in windfetch may also have servedto decrease watercolumn turbidity through its effect on theincidence of long-period swell. These processes may be reinforcedby associated changes in the quantity of turbid runoff dischargedby the Rhine. The advanced blooms of Ceratium spp. in the early1970s are attributed both to these effects and to an increasedfrequency of light winds (decreased wind mixing) in the earlymonths of the year.     

Influence of environmental factors on shot put and hammer throw range

On the rotating Earth, in addition to the Newtonian gravitational force, two additional relevant inertial forces are induced, the centrifugal and Coriolis forces. Using computer modelling for typical release heights and optimal release angles, we compare the influence of Earth rotation on the range of the male hammer throw and shot put with that of air resistance, wind, air pressure and temperature, altitude and ground obliquity. Practical correction maps are presented, by which the ranges achieved at different latitudes and/or with different release directions can be corrected by a term involving the effect of Earth rotation. Our main conclusion and suggestion is that the normal variations of certain environmental factors can be substantially larger than the smallest increases in the world records as acknowledged by the International Amateur Athletic Federation and, therefore, perhaps these should be accounted for in a normalization and adjustment of the world records to some reference conditions. Although this suggestion has certainly been made before, the comprehensiveness of our study makes it even more compelling. Our numerical calculations contribute to the comprehensive understanding and tabulation of these effects, which is largely lacking today.     

Influence of counterions radius on the polymerization of actin

The G–F transformation of actin was studied in terms of an interaction between different counterions and actin. macroion by means of electrometric measurements. Due to the polyelectrolyte-structure of the actin molecule, the electrostatic interactions must play a predominant role. In this sense the influence of the counterion radius has been investigated.     

Influence of closed skill and open skill warm-ups on the performance of speed, change of direction speed, vertical jump, and reactive agility in team sport athletes

In this study, we evaluated the efficacy of two different dynamic warm-up conditions, one that was inclusive of open skills (i.e., reactive movements) and one that included only preplanned dynamic activities (i.e., closed skills) on the performance of speed, change of direction speed, vertical jump, and reactive agility in team sport athletes. Fourteen (six male, eight female) junior (mean +/- SD age, 16.3 +/- 0.7 year) basketball players participated in this study. Testing was conducted on 2 separate days using a within-subjects cross-over study design. Each athlete performed a standardized 7-minute warm-up consisting of general dynamic movements and stretching. After the general warm-up, athletes were randomly allocated into one of two groups that performed a dynamic 15-minute warm-up consisting entirely of open or closed skills. Each of the warm-up conditions consisted of five activities of 3 minute duration. At the completion of the warm-up protocol, players completed assessments of reactive agility, speed (5-, 10-, and 20-m sprints), change of direction speed (T-test), and vertical jump. No significant differences (p > 0.05) were detected among warm-up conditions for speed, vertical jump, change of direction speed, and reactive agility performances. The results of this study demonstrate that either open skill or closed skill warm-ups can be used effectively for team sport athletes without compromising performance on open skill and closed skill tasks.     

Influence of gait speed on the control of mediolateral dynamic stability during gait initiation

This study investigated the influence of gait speed on the control of mediolateral dynamic stability during gait initiation. Thirteen healthy young adults initiated gait at three self-selected speeds: Slow, Normal and Fast. The results indicated that the duration of anticipatory postural adjustments (APA) decreased from Slow to Fast, i.e. the time allocated to propel the centre of mass (COM) towards the stance-leg side was shortened. Likely as an attempt at compensation, the peak of the anticipatory centre of pressure (COP) shift increased. However, COP compensation was not fully efficient since the results indicated that the mediolateral COM shift towards the stance-leg side at swing foot-off decreased with gait speed. Consequently, the COM shift towards the swing-leg side at swing heel-contact increased from Slow to Fast, indicating that the mediolateral COM fall during step execution increased as gait speed rose. However, this increased COM fall was compensated by greater step width so that the margin of stability (the distance between the base-of-support boundary and the mediolateral component of the “extrapolated centre of mass”) at heel-contact remained unchanged across the speed conditions. Furthermore, a positive correlation between the mediolateral extrapolated COM position at heel-contact and step width was found, indicating that the greater the mediolateral COM fall, the greater the step width. Globally, these results suggest that mediolateral APA and step width are modulated with gait speed so as to maintain equivalent mediolateral dynamical stability at the time of swing heel-contact.     

The 3D path of body centre of mass during adult human walking on force treadmill

Three-dimensional (3D) path of the body centre of mass (CM) over an entire stride was computed from ground reaction forces during walking at constant average speed on a treadmill mounted on 3D force sensors. Data were obtained from 18 healthy adults at speeds ranging from 0.30 to 1.40 m s^?1, in 0.1 m s^?1 increments. Six subsequent strides were analyzed for each subject and speed (total strides=1296). The test session lasted about 30 min (10 min for walking). The CM path had an upward concave figure-of-eight shape that was highly consistent within and across subjects. Vertical displacement of the CM increased monotonically as a function of walking speed. The forward and particularly lateral displacements of the CM showed a U-shaped relationship to speed. The same held for the total 3D displacement (25.6–16.0 cm, depending on the speed). The results provide normative benchmarks and suggest hypotheses for further physiologic and clinical research. The familiar inverted pendulum model might be expanded to gyroscopic, “spin-and-turn” models. Abnormalities of the 3D path might flag motor impairments and recovery.     

Eccentric exercise increases EMG amplitude and force fluctuations during submaximal contractions of elbow flexor muscles.

The purpose of this study was to determine the effect of eccentric exercise on the ability to exert steady submaximal forces with muscles that cross the elbow joint. Eight subjects performed two tasks requiring isometric contraction of the right elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at four submaximal target forces (5, 20, 35, 50% MVC) while electromyography (EMG) was recorded from elbow flexor and extensor muscles. These tasks were performed before, after, and 24 h after a period of eccentric (fatigue and muscle damage) or concentric exercise (fatigue only). MVC force declined after eccentric exercise (45% decline) and remained depressed 24 h later (24%), whereas the reduced force after concentric exercise (22%) fully recovered the following day. EMG amplitude during the submaximal contractions increased in all elbow flexor muscles after eccentric exercise, with the greatest change in the biceps brachii at low forces (3-4 times larger at 5 and 20% MVC) and in the brachialis muscle at moderate forces (2 times larger at 35 and 50% MVC). Eccentric exercise resulted in a twofold increase in coactivation of the triceps brachii muscle during all submaximal contractions. Force fluctuations were larger after eccentric exercise, particularly at low forces (3-4 times larger at 5% MVC, 2 times larger at 50% MVC), with a twofold increase in physiological tremor at 8-12 Hz. These data indicate that eccentric exercise results in impaired motor control and altered neural drive to elbow flexor muscles, particularly at low forces, suggesting altered motor unit activation after eccentric exercise.     

The effect of attempted ballistic training on the force and speed of movements

Athletes in sports requiring explosive movements might benefit from a unique form of training in which a limb is restrained while the athlete attempts ballistic (explosive) movements. We investigated the effects of such ballistic training and conventional resistance training on force and speed of front kicks, side kicks, and palm strikes of martial artists. We assigned subjects randomly to an experimental group (n = 13) or a control (normal martial art training) group (n = 9). Conventional resistance training produced a gain of 12% (95% likely limits +/- 13%) in front kick force relative to the control group. Overall ballistic training and conventional resistance training decreased side kick force by 15% (+/-14%), but movement speeds increased by 11-21% (+/-13-17%). Responses to ballistic training were generally more marked in more highly skilled athletes. Attempted ballistic training may be a beneficial adjunct to resistance training for skilled athletes in sports where speed rather than force is critical.     

Effects of wind speed and direction on monthly fluctuations of <Emphasis Type="Italic">Cladosporium</Emphasis> conidia concentration in the air

This study determined the relationship between airborne concentration of Cladosporium spp. spores and wind speed and direction using real data (local wind measured by weather station) and modelled data (air mass flow computed with the aid of HYbrid Single Particle Lagrangian Trajectory model). Air samples containing fungal conidia were taken at an urban site (Worcester, UK) for a period of five consecutive years using a spore trap of the Hirst design. A threshold of ≥6000 s m^?3 (double the clinical value) was applied in order to select high spore concentration days, when airborne transport of conidia at a regional scale was more likely to occur. Collected data were then examined using geospatial and statistical tools, including circular statistics. Obtained results showed that the greatest numbers of spore concentrations were detected in July and August, when C. herbarum, C. cladosporioides and C. macrocarpum sporulate. The circular correlation test was found to be more sensitive than Spearman’s rank test. The dominance of either local wind or the air mass on Cladosporium spore distributions varied between examined months. Source areas of this pathogen had an origin within the UK territory. Very high daily mean concentrations of Cladosporium spores were observed when daily mean local wind speed was v _s ≤ 2.5 m s^?1 indicating warm days with a light breeze.     

Testing visual sensitivity to the speed and direction of motion in lizards

Testing visual sensitivity in any species provides basic information regarding behaviour, evolution, and ecology. However, testing specific features of the visual system provide more empirical evidence for functional applications. Investigation into the sensory system provides information about the sensory capacity, learning and memory ability, and establishes known baseline behaviour in which to gauge deviations (Burghardt, 1977). However, unlike mammalian or avian systems, testing for learning and memory in a reptile species is difficult. Furthermore, using an operant paradigm as a psychophysical measure of sensory ability is likewise as difficult. Historically, reptilian species have responded poorly to conditioning trials because of issues related to motivation, physiology, metabolism, and basic biological characteristics. Here, I demonstrate an operant paradigm used a novel model lizard species, the Jacky dragon (Amphibolurus muricatus) and describe how to test peripheral sensitivity to salient speed and motion characteristics. This method uses an innovative approach to assessing learning and sensory capacity in lizards. I employ the use of random-dot kinematograms (RDKs) to measure sensitivity to speed, and manipulate the level of signal strength by changing the proportion of dots moving in a coherent direction. RDKs do not represent a biologically meaningful stimulus, engages the visual system, and is a classic psychophysical tool used to measure sensitivity in humans and other animals. Here, RDKs are displayed to lizards using three video playback systems. Lizards are to select the direction (left or right) in which they perceive dots to be moving. Selection of the appropriate direction is reinforced by biologically important prey stimuli, simulated by computer-animated invertebrates.     

Strength training reduces force fluctuations during anisometric contractions of the quadriceps femoris muscles in old adults.

The greater fluctuations in motor output that are often exhibited by old adults can be reduced with strength training. The purpose of the study was to determine the effect of strength and steadiness training by old adults on fluctuations in force and position during voluntary contractions with the quadriceps femoris muscle. Healthy old adults (65-80 yr) completed 16 wk of heavy-load (80% of maximum, n = 11) strength training, heavy-load steadiness training (n = 6), or no training (n = 9). Steadiness training required subjects to match the angular displacement about the knee joint to a constant-velocity template. The Heavy-Load group experienced a 5.5% increase in muscle volume, a 25% increase in maximal voluntary contraction force, and a 26% increase in the one-repetition (1-RM) load. The Heavy-Load Steady group experienced increases of 11.5, 31, and 36%, respectively. The maximal electromyogram signal of quadriceps femoris increased by 51% in the two training groups. The coefficient of variation (CV) for force during submaximal isometric contractions did not change with training for any group. Although both training groups also experienced a reduction in CV for force during anisometric contractions with a 50% 1-RM load, the standard deviation of position did not change with time for any group. The Heavy-Load Steady group also experienced a reduction in CV for force during the training contractions performed with the 80% 1-RM load. Thus strength training reduced the force fluctuations of the quadriceps femoris muscles during anisometric contractions but not during isometric contractions.     

Path curvature discrimination: dependence on gaze direction and optical flow speed

Many experimental approaches to the control of steering rely on the tangent point (TP) as major source of information. The TP is a good candidate to control self-motion. It corresponds to a singular and salient point in the subject's visual field, and its location depends on the road geometry, the direction of self-motion relative to the road and the position of the driver on the road. However, the particular status of the TP in the optical flow, as a local minimum of flow speed, has often been left aside. We therefore assume that the TP is actually an optimal location in the dynamic optical array to perceive a change in the trajectory curvature. In this study, we evaluated the ability of human observers to detect variations in their path curvature from optical flow patterns, as a function of their gaze direction in a virtual environment. We simulated curvilinear self-motion parallel to a ground plane. Using random-dot optic flow stimuli of brief duration and a two-alternative forced-choice adaptive procedure, we determined path curvature discrimination thresholds, as a function of gaze direction. The discrimination thresholds are minimal for a gaze directed toward a local minimum of optical flow speed. A model based on Weber fraction of the foveal velocities (ΔV/V) correctly predicts the relationship between experimental thresholds and local flow velocities. This model was also tested for an optical flow computation integrating larger circular areas in central vision. Averaging the flow over five degrees leads to an even better fit of the model to experimental thresholds. We also found that the minimal optical flow speed direction corresponds to a maximal sensitivity of the visual system, as predicted by our model. The spontaneous gazing strategies observed during driving might thus correspond to an optimal selection of relevant information in the optical flow field.     

Triple-loop model of path control by head direction and place cells

 Arthropods as well as mammals are able to return straight home after a random search excursion under conditions that are designed to exclude all external cues. After a brief clarification of the terminology, two principal systems of information processing that can achieve this performance are introduced and analysed: Polar versus Cartesian path integration. The different demands and achievements of the two systems are confronted with neurophysiological findings on the functioning of the hippocampus, and with a recent comprehensive model of how the hippocampal place cells perform path integration. To connect the neurophysiological findings with the behavior of the animal, a new model is developed. It achieves three functionally diverse performances: maintenance and control of a compass direction, navigation by path integration, and formation of goals by connecting non-spatial features with their location. This is done by three interconnected feedback loops, set by a common reference variable. Their information-processing structure enables the animal not only to home but also to go straight from any stored goal to any other, without explicit representation of the distance between them, and without a topological arrangement of the store. The model explains behaviors not yet understood and predicts still undiscovered performances. Because it allows the isolation of orienting from storing functions yet also shows how they can be connected, the model may help to reconcile conflicting views on the function of the hippocampus. Received: 17 June 1999 / Accepted in revised form: 20 March 2000     

Influence of wind direction on pollen concentration in the atmosphere

The daily pollen concentration in the atmosphere of Badajoz (SW Spain) was analysed over a 6-year period (1993–1998) using a volumetric aerobiological trap. The results for the main pollination period are compared with the number of hours of wind each day in the four quadrants: 1 (NE), 2 (SE), 3 (SW) and 4 (NW). The pollen source distribution allowed 16 pollen types to be analysed as a function of their distribution in the four quadrants with respect to the location of the trap. Four of them correspond to species growing in an irrigated farmland environment (Amaranthaceae-Chenopodiaceae, Plantago, Scirpus, and Typha), five to riparian and woodland species (Salix, Fraxinus, Alnus, Populus, and Eucalyptus), four to urban ornamentals (Ulmus, Arecaceae, Cupressaceae, and Casuarina), and three which include the most frequent pollen grains of widely distributed species (Poaceae, Quercus, and Olea). The results show that the distribution of the sources and the wind direction play a very major role in determining the pollen concentration in the atmosphere when these sources are located in certain quadrants, and that the widely distributed pollen sources show no relationship with wind direction. In some years the values of the correlations were not maintained, which leads one to presume that, in order to draw significant conclusions and establish clear patterns of the influence of wind direction, a continuous and more prolonged study will be required. Received: 6 May 1999 / Revised: 30 March 2000 / Accepted: 31 March 2000