Gliding Phase Research Articles

Gas gangrene-associated gliding motility is regulated by the Clostridium perfringens CpAL/VirSR system

Clostridium perfringens strains cause a wide variety of human and animal disease, including gas gangrene or myonecrosis. Production of toxins required for myonecrosis, PFO and CPA, is regulated by the C. perfringens Agr-like (CpAL) system via the VirSR two-component system. Myonecrosis begins at the site of infection from where bacteria migrate deep into the host tissue likely using a previously described gliding motility phenotype. We therefore assessed whether gliding motility was under the control of the CpAL/VirSR regulon. The migration rate of myonecrosis-causing C. perfringens strain 13 (S13) was investigated during a 96 h period, including an adaptation phase with bacterial migration (∼1.4 mm/day) followed by a gliding phase allowing bacteria faster migration (∼8.6 mm/day). Gliding required both an intact CpAL system, and signaling through VirSR. Mutants lacking ΔagrB, or ΔvirR, were impaired for onward gliding while a complemented strain S13ΔagrB/pTS1303 had the gliding phenotype restored. Gene expression studies revealed upregulated transcription of pili genes (pilA1, pilA2 and pilT) whose encoded proteins were previously found to be required for gliding motility and CpAL/VirSR-regulated pfoA and cpa toxin genes. Compared to S13, transcription of cpa and pfoA significantly decreased in S13ΔagrB, or S13ΔvirR, strains but not that of pili genes. Further experiments demonstrated that mutants S13ΔpfoA and S13Δcpa migrated at the same rate as S13 wt. We demonstrated that CpAL/VirSR regulates C. perfringens gliding motility and that gliding bacteria have an increased transcription of toxin genes involved in myonecrosis.

Improving data acquisition speed and accuracy in sport using neural networks

ABSTRACT Video analysis is used in sport to derive kinematic variables of interest but often relies on time-consuming tracking operations. The purpose of this study was to determine speed, accuracy and reliability of 2D body landmark digitisation by a neural network (NN), compared with manual digitisation, for the glide phase in swimming. Glide variables including glide factor; instantaneous hip angles, trunk inclines and horizontal velocities were selected as they influence performance and are susceptible to digitisation propagation error. The NN was “trained” on 400 frames of 2D glide video from a sample of eight elite swimmers. Four glide trials of another swimmer were used to test agreement between the NN and a manual operator for body marker position data of the knee, hip and shoulder, and the effect of digitisation on glide variables. The NN digitised body landmarks 233 times faster than the manual operator, with digitising root-mean-square-error of ~4-5 mm. High accuracy and reliability was found between body position and glide variable data between the two methods with relative error ≤5.4% and correlation coefficients >0.95 for all variables. NNs could be applied to greatly reduce the time of kinematic analysis in sports and facilitate rapid feedback of performance measures.

Glide Time Relates to Mediolateral Plantar Pressure Distribution Rather Than Ski Edging in Ski Skating.

The purpose of this study was (i) to assess the differences in relative glide time and both ski edging angle and plantar pressure mediolateral distribution in skiers of different levels and (ii) to further investigate the relationships between the aforementioned variables. Twelve male cross-country skiers (6 national and 6 regional level) skied at 4.2 m s−1 on a 2.5° uphill snow track using the V2 technique. The relative glide time (in percentage of contact time) and mediolateral plantar pressure distribution variables (asymmetry index, ASI) were derived from pressure insole measurements. Ski edging angle variables were calculated from an Inertial Measurement Unit placed on the ski. Minimum, maximum, mean, and range of both ASI and ski edging angle were computed over the gliding phase, giving information about the beginning, end, and throughout the gliding phase. Relative glide time was significantly higher, and minimum and mean ASI were significantly lower in the national- than in the regional-level skiers. Relative glide time was strongly negatively correlated to minimum ASI (i.e., plantar pressure mostly on the foot lateral side at the beginning of gliding phase) and strongly positively correlated to ASI range. These results may reflect a larger body mass transfer above the ski from the beginning of the gliding phase to increase gliding, especially in the national-level skiers. Ski edging angle seems less relevant to discriminate skiers' level of performance. These results have direct consequences on how technique must be taught to young cross-country skiers.

Giant Slalom: Analysis of Course Setting, Steepness and Performance of Different Age Groups - A Pilot Study.

Introduction: Giant slalom is the core discipline of alpine skiing, and each race has its own specific course and terrain characteristics. These variations may explain differences in the speed and time per turn profiles, which are essential for performance development and injury prevention. This study aims to address the differences in course setting and steepness of the different course sections (flat—medium—steep) and compare them to the performance parameters among young (U12, U14, U16) and older (U18, U21, elite) male athletes.Methods: The study examined a total sample size of 57 male athletes; 7 from elite level, 11 from U21, 13 from U18, 6 from U16, 13 from U14, and 7 from U12. The athletes wore a portable global navigation satellite system (GNSS) sensor to extract performance parameters. The course profiles and gate positions of nine runs were measured with differential GNSS. The runs were divided into flat, medium and steep sections. From the performance parameters (speed, time per turn, etc.) and the course setting variables, the mean value per section was calculated and used for the further analysis.Results: In total, 192 run sections from 88 runs were recorded and analyzed. Comparisons between course settings in young and older classes showed no significant differences. However, the turning angles and horizontal gate distances were smaller in flat sections. Average speed (49.77 vs. 65.33 km/h) and time per turn (1.74 vs. 1.41 s) differed significantly between young and U21/elite categories. In medium terrain sections U21 and elite athletes spent more time in the gliding phase compared to all other athletes.Discussion: It seems to be a reasonable that, given similar course setting and steepness, speed increases concurrently with the technical and tactical skills of the athlete. Moreover, the finding that the elite athletes spent more time in the gliding phase could be crucial for understanding technique and performance development in young athletes.

A novel reduced-order guidance and control scheme for hypersonic gliding vehicles

A novel analytical model between roll, pitch rates and components of acceleration of the hypersonic vehicle is established, and a reduced-order gliding guidance and control (G&C) design approach for the hypersonic vehicle is proposed in this paper. The six-degree-of-freedom (6DOF) dynamical and kinematic equations of the hypersonic vehicle in the gliding phase are described. An analytical model suitable for the bank to turn (BTT) control strategy is derived by connecting body rates with components of acceleration in the ballistic coordinate system. A novel reduced-order guidance and control design model with respect to quasi-equilibrium gliding flight is deduced and converted into the strict feedback form. The three channel body rates are treated as pseudo-inputs for tracking errors of flight path angle and heading angle of the hypersonic vehicle. Then, the commanded control surface fin deflections of the hypersonic vehicle are obtained by controlling tracking errors of the flight path angle, heading angle, and the body rates by adopting the block dynamic surface control method. In this paper, the aerodynamic coefficient interpolation process for obtaining the commanded angle of attack and bank angle based on expectant guidance overload is avoided. Meanwhile, the control loop of tracking Euler angles for getting the desired body rates is also elided. Finally, effectiveness and robustness of the novel G&C design method are verified and investigated. Moreover, the feasibility of entering quasi-equilibrium gliding phase only depending on the aerodynamic control mechanism is discussed.

A framework of trajectory design and optimization for the hypersonic gliding vehicle

Trajectory of Hypersonic Gliding Vehicles (HGV) designed and optimized generally is an especial path with actual task requirements, which mostly provide feasible flight information for the design of guidance and control system. This paper mainly presents a framework of trajectory design and optimization for HGV, and differences between design and optimization results are discussed. In the first part of the framework, the trajectory is designed mainly by the programming angle commands. Specifically, the pitch angle as the control variable in the boost phase, and the angle of attack (AOA) as the control variable in the glide phase are considered. Then, establishing a trajectory optimization model, which has coincident initial and terminal conditions with the trajectory design part if it's reasonable, and additional constraints. Applying a Legendre-Gauss-Radau (LGR) orthogonal collocation method for solving the problem. In this part, Firstly, low density collocation points are set in the algorithm to find the feasible trajectory, and then further increase the density of collocation points to optimize to get more information about the state and control of the trajectory points. Finally, several initial parameters of the glide phase are discussed, which have a great influence on the flight performance. Numerical simulation indicates that the effectiveness of the proposed framework for the real task scenarios is amazing.

Reentry guidance by accelerated fractional-order particle swarm optimization method

PurposeThe aim of this study is to design a guidance method to generate a smoother and feasible gliding reentry trajectory, a highly constrained problem by formalizing the control variables profile.Design/methodology/approachA novel accelerated fractional-order particle swarm optimization (FAPSO) method is proposed for velocity updates to design the guidance method for gliding reentry flight vehicles with fixed final energy.FindingsBy using the common aero vehicle as a test case for the simulation purpose, it is found that during the initial phase of the longitudinal guidance, there are oscillations in the state parameters which cause to violate the path constraints. For the glide phase of the longitudinal guidance, the path constraints have higher values because of the increase in the atmosphere density.Research limitations/implicationsThe violation in the path constraints may compromise the flight vehicle safety, whereas the enforcement assures the flight safety by flying it within the reentry corridor.Originality/valueAn oscillation suppression scheme is proposed by using the FAPSO method during the initial phase of the reentry flight, which smooths the trajectory and enforces the path constraints partially. To enforce the path constraints strictly in the glide phase, ultimately, another scheme by using the FAPSO method is proposed. The simulation results show that the proposed algorithm is efficient to achieve better convergence and accuracy for nominal as well as dispersed conditions.

Deformation mechanisms and crack routes of CrAlN coatings

CrAlN coatings possess high hardness and thermal stability, but also increased brittleness due to strong covalent AlN bonding. With poor plasticity due to frozen perfect dislocation activities, individual columnar grain acts as the fundamental deformation element that controls overall deformation via grain boundary activities. Damage tolerance can be thus improved by high compressive stress that hinders grain boundary glide and volume-dilation phase transition. By investigating deformation structure, we also found that zigzagged cracking modes might be attributed to atomic-scale hardening heterogeneity. Additionally, stress-induced nano-twinning was found, which also contributes to the improved fracture resistance.

An Analysis of the Tradeoff Between Fuel Consumption and Ride Comfort for the Pulse and Glide Driving Strategy

Pulse and glide (PnG) is a driving strategy that controls vehicles in a more fuel-efficient way than driving at a constant speed does. It can be applied by the driver or, which is more likely, by an automated system with autonomy level one or higher. During the pulse phase, the vehicle is accelerated to operate the combustion engine and transmission at higher efficiency. During the following glide phase, the vehicle decelerates and the engine is decoupled from the drive train. The optimal pulse and glide strategy – as addressed in previous studies – implies high acceleration values and abrupt transitions between pulse and glide, which both degrade the ride comfort. A driveability study on PnG conducted recently identified that the acceleration, the jerk during the transitions and the duration of the glide phase have to be limited to reach the desired level of ride comfort. Thresholds have been derived for a level-eight calibration, i.e. a PnG operation that is noticeable only to skeptical customers. We use the results of the study to also provide thresholds for a level-seven calibration, i.e. a PnG operation that is noticeable to all customers without being disturbing. Subsequently, we establish a correlation between ride comfort and fuel consumption by comparing the fuel savings of three different driveability calibrations: level eight, level seven and a calibration without driveability constraints. The simulations are performed for a D-segment vehicle and two different gasoline engines. With reference to constant speed, the fuel savings of the level-seven calibration are larger than 30% below 40 km/h, decreasing gradually with increasing speed. They are around ten percent higher than those of the level-eight calibration and only a few percent lower than those of a PnG operation without driveability constraints. Hence, the level-seven calibration can nearly exploit the maximal fuel-saving potential of PnG, and, as it is not disturbing, should be considered for practical applications of PnG. The PnG strategy can be applied to any vehicle equipped with a combustion engine that features the engine-off functionality, which is the case for mild and full hybrids and for some micro hybrids. However, considering that the benefit of PnG increases with increasing engine size, the fuel saving potential of PnG is highest for micro and mild hybrids as these vehicles are commonly equipped with larger engines than full hybrids.

Microstructure evolution and adiabatic heating during dynamic biaxial deformation of a 304 stainless steel

This study focuses on the microstructure evolution and adiabatic heating during high strain rate biaxial deformation of a 304 stainless steel. Adiabatic heating is measured in situ during drop weight impact testing of the studied material. The considerable temperature rise induced by adiabatic heating (up to 184.3 °C when impacted with 140 J) is detected. The microstructure was analyzed by X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) techniques. Dislocation glide, twinning and austenite-martensite phase transformation are operating during high strain rate plastic deformation. The XRD analysis shows a steady increase of α′-martensite fraction (up to 36%) with plastic strain (up to 0.8), whereas the fraction of intermediate ε-martensite remains negligible (<0.5%). The biaxial stress compensated the possible impediment of martensitic transformation caused by adiabatic heating and the increasing stacking fault energy (SFE). Nanotwins having a width of ~5 nm–~20 nm are inhomogeneously distributed in the microstructure. Interrelationship between adiabatic heating, deformation mechanisms and microstructure evolution is discussed.

Improving estimates of diving lung volume in air-breathing marine vertebrates.

The air volume in the respiratory system of marine tetrapods provides a store of O2 to fuel aerobic metabolism during dives; however, it can also be a liability, as the associated N2 can increase the risk of decompression sickness. In order to more fully understand the physiological limitations of different air-breathing marine vertebrates, it is therefore important to be able to accurately estimate the air volume in the respiratory system during diving. One method that has been used to do so is to calculate the air volume from glide phases - periods of movement during which no thrust is produced by the animal - which many species conduct during ascent periods, when gases are expanding owing to decreasing hydrostatic pressure. This method assumes that there is conservation of mass in the respiratory system, with volume changes only driven by pressure. In this Commentary, we use previously published data to argue that both the respiratory quotient and differences in tissue and blood gas solubility potentially alter the mass balance in the respiratory system throughout a dive. Therefore, near the end of a dive, the measured volume of gas at a given pressure may be 12-50% less than from the start of the dive; the actual difference will depend on the length of the dive, the cardiac output, the pulmonary shunt and the metabolic rate. Novel methods and improved understanding of diving physiology will be required to verify the size of the effects described here and to more accurately estimate the volume of gas inhaled at the start of a dive.

Glide guidance for reusable launch vehicles using analytical dynamics

This paper proposes a novel glide guidance law for the reusable launch vehicle (RLV), in which longitudinal and lateral paths are separately designed to quickly derive guidance commands. First, an altitude profile is designed in the longitudinal plane. Using this profile, the terminal altitude, flight path angle, and position are naturally met and the quasi-equilibrium glide condition (QEGC) is easily satisfied. Second, analytical solutions of altitude, velocity, and flight path angle are deduced in the glide phase; so the values of path constraints and performance index can also be analytical calculated. Third, a new concept of virtual target is proposed to design the lateral motion. By analytically determining the virtual target with the solutions in the glide phase, the cross-range is online adjusted to control the dissipation in velocity. Finally, the guidance law is proposed based on these analytical solutions. In the guidance law, longitudinal and lateral motions are controlled by online updating the profile and revising the virtual target, respectively. Integration-based predictors are unnecessary in comparison with conventional guidance laws, so a short guidance period can be used to improve the robustness. The effectiveness and the robustness of the proposed method are demonstrated with various scenarios and Monte Carlo simulation, respectively.

Kinematic analysis of the kick start from OSB12

Introduction: Start performance in swimming plays a major role in determining the final standings, especially in sprint races. The purpose of the study was to determine kinematic parameters underlying the kick start from OSB12 in terms of the kick plate position and shoulder positioning at the start. Material and methods: The sample included 8 non-randomly recruited performance-level swimmers whose average age, body height, and body weight was 17.4 ± 1.8 years, 182.2 ± 3.4 cm and 81.00 ± 3.9 kg, respectively. To measure the kinematic parameters, we used the SwimPro camera system. The parameter rs measured included angular parameters and kinematic parameters for each of the start phases: block phase, flight phase, and water phase. We processed the collected biomechanical data using the Statistica 12.0 software. To determine significant differences between the kick plate positions in three types of start, we applied the Mann-Whitney U test. Results: We found significant differences (p&lt;0.05) in the selected kinematic parameters in all phases, which depended on the OSB12 kick plate position and basic starting position (front-, neutral-, and rear-weighted). The greatest differences in the parameters measured were found between the front-weighted start and rear-weighted start. We may conclude that performance-level swimmers should adjust the rear kick plate to positions 3 and 4 and assume the following starting position: front knee angle between 131° and 133°, rear knee angle around 80°, and trunk angle between 40° and 41°. This starting position affects the flight phase, namely takeoff angle (40⁰-41⁰), head position at takeoff (1.33-1.38 m), flight time and distance (0.346-0.368 s; 2.74-2.79 m), entry angle (38⁰). The starting position also affects the glide phase, namely the glide time and distance (0.532-0.536 s; 2.22-2.26 m) and maximum depth (-0.91-0.92 m). Conclusions: The results of the study show that swimmers produced shorter times to 5 meters and higher velocity at 5 meters compared with other starting positions and OSB12 kick plate positions.

Stabilization for a chain of saturating integrators arising in the visual landing of aircraft with sampling

We provide a new output feedback control design for a chain of saturating integrators with imprecise output measurements where the outputs can also contain delays and sampling. Using a backstepping approach that leads to pointwise delays in the control and a dynamic extension, we prove input-to-state stability using a new dynamic extension approach. We utilize our main result to solve a problem in the visual landing of aircraft in the glide phase in the presence of delayed and sampled image processing.

Flight, symmetry and barb angle evolution in the feathers of birds and other dinosaurs.

There has been much discussion over whether basal birds (e.g. Archaeopteryx and Confuciusornis) exhibited active flight. A recent study of barb angles has suggested they likely could not but instead may have exhibited a gliding phase. Pennaceous primary flight feathers were proposed to show significant shifts in barb angle values of relevance to the inference of flight in these extinct taxa. However, evolutionary trends in the evolution of these barb angle traits in extant volant taxa were not analysed in a phylogenetic frame. Neither the ancestral crown avian condition nor the condition in outgroup dinosaurs with symmetrical feathers were assessed. Here, we expand the fossil sample and reanalyse these data in a phylogenetic frame. We show that extant taxa, including strong flyers (e.g. some songbirds), show convergence on trailing barb angles and barb angle asymmetry observed in Mesozoic taxa that were proposed not to be active fliers. Trailing barb angles in these Mesozoic taxa are similar to symmetrical feathers in outgroup dinosaurs, indicating that selective regimes acted to modify primarily the leading-edge barb angles. These trends inform dynamics in feather shape evolution and challenge the notion that barb angle and barb angle ratios in extant birds directly inform the reconstruction of function in extinct stem taxa.

Efferent modulation of spontaneous lateral line activity during and after zebrafish motor commands.

Accurate sensory processing during movement requires the animal to distinguish between external (exafferent) and self-generated (reafferent) stimuli to maintain sensitivity to biologically relevant cues. The lateral line system in fishes is a mechanosensory organ that experiences reafferent sensory feedback, via detection of fluid motion relative to the body generated during behaviors such as swimming. For the first time in larval zebrafish (Danio rerio), we employed simultaneous recordings of lateral line and motor activity to reveal the activity of afferent neurons arising from endogenous feedback from hindbrain efferent neurons during locomotion. Frequency of spontaneous spiking in posterior lateral line afferent neurons decreased during motor activity and was absent for more than half of swimming trials. Targeted photoablation of efferent neurons abolished the afferent inhibition that was correlated to swimming, indicating that inhibitory efferent neurons are necessary for modulating lateral line sensitivity during locomotion. We monitored calcium activity with Tg(elav13:GCaMP6s) fish and found synchronous activity between putative cholinergic efferent neurons and motor neurons. We examined correlates of motor activity to determine which may best predict the attenuation of afferent activity and therefore what components of the motor signal are translated through the corollary discharge. Swim duration was most strongly correlated to the change in afferent spike frequency. Attenuated spike frequency persisted past the end of the fictive swim bout, suggesting that corollary discharge also affects the glide phase of burst and glide locomotion. The duration of the glide in which spike frequency was attenuated increased with swim duration but decreased with motor frequency. Our results detail a neuromodulatory mechanism in larval zebrafish that adaptively filters self-generated flow stimuli during both the active and passive phases of locomotion.NEW & NOTEWORTHY For the first time in vivo, we quantify the endogenous effect of efferent activity on afferent gain control in a vertebrate hair cell system during and after locomotion. We believe that this pervasive effect has been underestimated when afferent activity of octavolateralis systems is characterized in the current literature. We further identify a refractory period out of phase with efferent control and place this gain mechanism in the context of gliding behavior of freely moving animals.

Aerodynamic study of the corrugated airfoil at ultra-low Reynolds number

In this study, Aeshna cyanea dragonfly forewing mid-cross-section corrugated airfoil was simulated at ultra-low Reynolds number. The corrugated airfoil was compared with its smooth counterpart to study the effect of the corrugations upon the aerodynamic performance. Unsteady two-dimensional laminar flow was solved using FLUENT. This study was divided into gliding phase and flapping phase. In the gliding phase, the corrugated airfoil produced a higher lift force with respect to the profiled airfoil at both tested Reynolds numbers ([Formula: see text], [Formula: see text]) with comparable drag coefficient for all the tested angles of attack. In the flapping phase, both the corrugated airfoil and the flat-plate have a very similar flow behavior which yields a very similar aerodynamic performance at Re[Formula: see text]. A structural analysis was performed to compare the corrugated airfoil with the flat-plate. The analysis revealed the superiority of the corrugated airfoil over the flat-plate in decreasing the deflection under the applied load. The reduced frequency was varied to study its impact on the aerodynamic performance. By increasing the reduced frequency, the thrust and the lift forces increased by [Formula: see text]% and [Formula: see text]%, respectively. Any increase in the reduced frequency will increase lift and thrust forces, but the propulsive efficiency will deteriorate.

Forces on hockey players: vectors, work, energy and angular momentum

Non-traditional examples can be very inspiring for students. This paper applies classical mechanics to different ways of skating in ice hockey. Skating blades glide easily along the ice in the direction of the blade. Horizontal forces on the skates are thus essentially perpendicular to the blade. Speed skaters glide long distances on each skate before pushing off for the next stride. A hockey player running for the puck may take a number quite short steps in a short explosive rush before shifting to longer strides, where the recurring need to change direction requires additional work by the skater. This paper investigates an alternative stride, with a longer gliding phase in a circular arc, where the centripetal force provided by the ice acting on the skates changes the direction of motion, without the need for additional energy. In addition, the conservation of angular momentum leads to increased speed as the centre of mass is shifted closer to the centre of the circular arc. Finally, we discuss an angular-momentum-based technique to reverse the direction of motion as fast as possible.

On the competition between dislocation transmission and crack nucleation at phase boundaries

The interaction of dislocations with phase boundaries is a complex phenomenon, that is far from being fully understood. A two-dimensional Peierls-Nabarro finite element (PN-FE) model for studying edge dislocation transmission across fully coherent and non-damaging phase boundaries was recently proposed. This paper brings a new dimension to the complexity by extending the PN-FE model with a dedicated cohesive zone model for the phase boundary. With the proposed model, a natural interplay between dislocations, external boundaries and the phase boundary, including decohesion of that boundary, is provided. It allows one to study the competition between dislocation transmission and phase boundary decohesion. Commonly, the interface potentials required for glide plane behaviour and phase boundary decohesion are established through atomistic simulations. They are corresponding to the misfit energy intrinsic to a system of two bulks of atoms that are translated rigidly with respect to each other. It is shown that the blind utilisation of these potentials in zero-thickness interfaces (as used in the proposed model) may lead to a large quantitative error. Accordingly, for physical consistency, the potentials need to be reduced towards zero-thickness potentials. In this paper a linear elastic reduction is adopted. With the reduced potentials for the glide plane and the phase boundary, the competition between dislocation transmission and phase boundary decohesion is studied for an 8-dislocation pile-up system. Results reveal a strong influence of the phase contrast in material properties as well as the phase boundary toughness on the outcome of this competition. In the case of crack nucleation, the crack length shows an equally strong dependency on these properties.

Skater's Cramp: A Possible Task-Specific Dystonia in Dutch Ice Skaters.

ABSTRACTBackgroundSkater's cramp is an involuntary lower leg movement in skilled speed skaters. We aim to evaluate whether skater's cramp is compatible with task‐specific dystonia.MethodsA case‐control study tested 5 speed skaters exhibiting symptoms of skater's cramp and 5 controls. Affected skaters completed a standardized questionnaire and neurological examination. Video analyses included skating normally, intensely, and with extra mass around the skater's ankles. An Inertial Motion Capturing (IMC) device mounted on both skates provided angular velocity data for both feet.ResultsMedian time of onset of skater's cramp occurred after 12 (range 3–22) years of speed skating. Skater's cramp appeared as task specific; its onset was sudden and correlated to stress and aberrant proprioception. Symptoms presented acutely and consistently during skating, unilaterally in 4 and bilaterally in 1 skater. Visually, skater's cramp was an active, patterned, and person‐specific jerking of a skater's foot, either exo‐ or endorotationally. It presented asymmetrically, repeating persistently as the foot neared the end of the swing phase. The skater's affected leg had a longer swing phase (median, 1.37 [interquartile range {IQR}, 0.35]/1.18 [IQR, 0.24] seconds; P < 0.01), a shorter glide phase (median, 1.09 [IQR, 0.25]/1.26 (IQR, 0.29) seconds; P < 0.01), and higher angular velocity during the jerking motion. Symptoms remained constant irrespective of speed or extra mass around the ankle (P > 0.05). No significant differences between legs were detected in the control group.ConclusionsObserved clinical, visual, and kinematic data could be an early and tentative indication of task‐specific dystonia.