Rapid Changes In Direction Research Articles

Curing Hydrodynamic Instability During Balanced Plug Cementing

Summary It is shown how the flow from pumping cement through an open-ended pipe very quickly changes direction and the cement flows upward. This rapid change in flow direction indicates that a diverter tool, which leads the cement slurry perpendicularly out of a closed-ended pipe, does not have any function. The placement of a balanced plug is feasible. However, a high-density fluid above a lighter fluid is not stable. The phenomenon is known as Rayleigh-Taylor instability. In principle, to be reasonably stable, the interface must be horizontal. The longer the interface is, the more unstable is this case. Thus, it is difficult, or sometimes impossible, to create a stable situation in a deviated well section, especially if the well section diameter is large. Observations show that it is possible to modify density differences, thickening time, and viscosity differences such that the success rate can be between 40% and 60%. Using a floatable cement foundation tool, this success rate increased to more than 95% in North Sea applications. The use of such a tool is described, and its performance is justified by a numerical analysis of cement flow.

Assessment of low‐frequency aeroacoustic emissions of a wind turbine under rapidly changing wind conditions based on an aero‐servo‐elastic CFD simulation

AbstractA meteorologically challenging situation that represents a demanding control task (rotational speed, pitch and yaw) for a wind turbine is presented and its implementation in a simulation is described. A high‐fidelity numerical process chain, consisting of the computational fluid dynamics (CFD) solver FLOWer, the multi‐body system (MBS) software SIMPACK and the Ffowcs Williams‐Hawkings code ACCO, is used. With it, the aerodynamic, servoelastic and aeroacoustic (<20 Hz) behaviour of a generic wind turbine during a meteorological event with strong and rapid changes in wind speed and direction is investigated. A precursor simulation with the meteorological model system PALM is deployed to generate realistic inflow data. The simulated strong controller response of the wind turbine and the resulting aeroelastic behaviour are analysed. Finally, the low‐frequency sound emissions are evaluated and the influence of the different operating and flow parameters during the variable inflow is assessed. It is observed that the wind speed and, linked to it, the rotational speed as well as the turbulence intensity are the main influencing factors for the emitted low‐frequency sound power of the wind turbine. Yawed inflow, on the other hand, has little effect unless it changes the operational mode to load reduction, resulting in a swap of the main emitter from the blades to the tower.

Rapid Change in the Direction of Hand Movement to Increase Hand Propulsion During Front Crawl Swimming.

This study aims to investigate the difference in hand acceleration induced by rapid changes in hand movement directions and propulsion between fast and slow groups of swimmers during front crawl swimming. Twenty-two participants, consisting of 11 fast and 11 slow swimmers, performed front crawl swimming at their maximal effort. Hand acceleration and velocity and the angle of attack were measured using a motion capture system. The dynamic pressure approach was used to estimate hand propulsion. In the insweep phase, the fast group attained significantly higher hand acceleration than the slow group in the lateral and vertical directions (15.31 [3.44]m·s-2 vs 12.23 [2.60]m·s-2 and 14.37 [1.70]m·s-2 vs 12.15 [1.21]m·s-2), and the fast group exerted significantly larger hand propulsion than the slow group (53 [5]N vs 44 [7]N). Although the fast group attained large hand acceleration and propulsion during the insweep phase, the hand velocity and the angle of attack were not significantly different in the 2 groups. The rapid change in hand movement direction could be considered in the technique of underwater arm stroke, particularly in the vertical direction, to increase hand propulsion during front crawl swimming.

Musculoskeletal Injuries in Ice Hockey: A Review of Epidemiology, Risk Factors, Mechanisms, and Rehabilitation

Hockey players must have good coordination skills, agility, and control of their body movements. The main movement pattern is the skating, which consists of a support and a swing phase. Those who skate effectively can reach speeds up to 48 km/h. Traumatic injuries predominate in hockey, with medial collateral ligament injury being the most common injury in both genders (44/1,000 h). Overuse injuries account for a smaller proportion of injuries, with the hip joint being the most affected area. One of the most important internal risk factors is a previous injury. External risk factors relate to the level of play, player position, and the characteristics of the game. Repetitive skating patterns can cause femoroacetabular impingement syndrome. Inadequate skating technique results in a knee valgus position, which can damage the medial collateral ligament. Rapid changes of direction cause an injury of the hip adductor muscles. Torsional forces in the ankle during skating can lead to high ankle fractures, and shear forces between the tendons and the stiff tongue of the skate can lead to tendon inflammation. Prevention activities should include strengthening of the hip, knee and shoulder girdle muscles, and sport-specific exercises early in the season. At the end of the article, rehabilitation strategies for specific injuries are also discussed.

GNSS Reconstrainted Visual–Inertial Odometry System Using Factor Graphs

Monocular vision sensors are often affected by the rapid direction change in load platform and violent illumination change when the mobile device moves autonomously with high maneuverability. The images collected by the visual sensor will also have a lot of dynamic blur, which together with the weak texture environment reduces the continuity and accuracy of the visual autonomous navigation system. To enhance the stability of the system, in the letter, we propose a vision-led multisource data fusion navigation algorithm. The system combines the visual information for trajectory estimation, adds the inertial measurement unit (IMU) measurement information to the sliding window for optimization, and finally uses the global navigation satellite system (GNSS) data as a reconstraint condition through factor graph optimization to further optimize the trajectory accuracy. Experiments on the public datasets containing a variety of different scene categories show that the trajectory tracking results generated by our algorithm are more complete and stable and can better meet the system’s autonomous navigation requirements.

The physiology of ice hockey performance: An update.

Ice hockey is an intense team sport characterized by repeated bursts of fast-paced skating, rapid changes in speed and direction and frequent physical encounters. These are performed in on-ice shifts of ~30-80 s interspersed with longer sequences of passive recovery, resulting in about 15-25 min on-ice time per player. Nearly 50% of the distance is covered at high-intensity skating speeds and with an accentuated intense activity pattern in forwards compared to defensemen. During ice hockey match-play, both aerobic and anaerobic energy systems are significantly challenged, with the heart rate increasing toward maximum levels during each shift, and with great reliance on both glycolytic and phosphagen ATP provision. The high-intensity activity pattern favors muscle glycogen as fuel, leading to pronounced reductions despite the relatively brief playing time, including severe depletion of a substantial proportion of individual fast- and slow-twitch fibers. Player-tracking suggests that the ability to perform high-intensity skating is compromised in the final stages of a game, which is supported by post-game reductions in repeated-sprint ability. Muscle glycogen degradation, in particular in individual fibers, as well as potential dehydration and hyperthermia, may be prime candidates implicated in exacerbated fatigue during the final stages of a game, whereas multiple factors likely interact to impair exercise tolerance during each shift. This includes pronounced PCr degradation, with potential inadequate resynthesis in a proportion of fast-twitch fibers in situations of repeated intense actions. Finally, the recovery pattern is inadequately described, but seems less long-lasting than in other team sports.

Method of Changing Running Direction of Cheetah-Inspired Quadruped Robot.

The rapid change of motion direction during running is beneficial to improving the movement flexibility of the quadruped robot, which is of great relevance to its research. How to make the robot change its motion direction during running and achieve good dynamic stability is a problem to be solved. In this paper, a method to change the running direction of the cheetah-inspired quadruped robot is proposed. Based on the analysis of the running of the cheetah, a dynamic model of the quadruped robot is established, and a two-level stability index system, including a minimum index system and a range index system, is proposed. On this basis, the objective function based on the stability index system and optimization variables, including leg landing points, trunk movement trajectory, and posture change rule, are determined. Through these constraints, the direction changes with good dynamic stability of the cheetah-inspired quadruped robot during running is realized by controlling the leg parameters. The robot will not roll over during high-speed movement. Finally, the correctness of the proposed method is proven by simulation. This paper provides a theoretical basis for the quadruped robot's rapid change of direction in running.

The dynamic, thermal and material structures of sea-land breeze circulation at the coastal of Ningbo, East China Sea

The high-resolution dynamic, thermal and material structures of sea-land breeze circulation (SLB) were observed at the coastal of Ningbo, East China Sea from November 2019 to May 2020, with wind profile lidar, microwave radiometer and particulate matter lidar. The results show that SLB occurs more frequently in spring (22 days) than in winter (18 days). The horizontal wind speed is generally less than 8 m·s−1, and the vertical wind speed is less than 0.17 m·s−1. The maximum U wind component is 3.2 m·s−1 and 2.4 m·s−1 in spring and winter, respectively. The U wind component and its gradient show that the circulation heights of sea breeze in winter and spring are 1.3 km and 1.8 km, respectively. The heights of land breeze (LB) in winter and spring are 0.65 km and 1.1 km, respectively. The horizontal wind speed shows that the prevailing heights of sea breeze (SB) in winter and spring are 0.9 km and 1.3 km, respectively. The prevailing heights of LB in winter and spring are 0.4 km and 0.7 km, respectively. The boundary layer height during SB is about 1.1 km, and the residual layer height during LB is about 0.6 km at night. The development of SLB in winter is obviously different from that in spring, the transition process is about 2 h shorter than that in spring. With the rapid change of wind speed and direction, the turbulent kinetic energy reaches 3.5m2·s−2 on about 1.0–1.2 km in the circulation. The maximum of TKE in spring is higher than that in winter. The changes of temperature and absolute humidity are similar in winter and spring. Particulate matter was confined within the boundary layer of SLB, much lower than the circulation height. When the SB speed increases, the PM10 concentration decreases. PM10 has a zonal distribution at 400 m in spring.

Exploring the limits to turning performance with size and shape variation in dogs.

Manoeuvrability, the ability to make rapid changes in direction, is central to animal locomotion. Turning performance may depend on the ability to successfully complete key challenges including: withstanding additional lateral forces, maintaining sufficient friction, lateral leaning during a turn and rotating the body to align with the new heading. We filmed high-speed turning in domestic dogs (Canis lupus familiaris) to quantify turning performance and explore how performance varies with body size and shape. Maximal speed decreased with higher angular velocity, greater centripetal acceleration and smaller turning radii, supporting a force limit for wider turns and a friction limit for sharp turns. Variation in turning ability with size was complex: medium sized dogs produced greater centripetal forces, had relatively higher friction coefficients, and generally aligned the body better with the heading compared with smaller and larger bodied dogs. Body shape also had a complex pattern, with longer forelimbs but shorter hindlimbs being associated with better turning ability. Further, although more crouched forelimbs were associated with an increased ability to realign the body in the direction of movement, more upright hindlimbs were related to greater centripetal and tangential accelerations. Thus, we demonstrate that these biomechanical challenges to turning can vary not only with changes in speed or turning radius, but also with changes in morphology. These results will have significant implications for understanding the link between form and function in locomotory studies, but also in predicting the outcome of predator-prey encounters.

Palynofacies and sea level changes in the Upper Cretaceous of the Yola Basin, Northern Benue Trough, Northeastern Nigeria

Upper Cretaceous sediments (Numanha and Lamja Formations) in the Yola basin of Northern Benue Trough have been investigated in order to characterize the particulate organic matter (POM) in the samples. The aim is to understand the rapid facies changes in both vertical and lateral direction of the formations and the relative abundance of the different organic components within the sections. The investigation involved 62 samples from four outcrop sections. The analysis involved series of laboratory procedure ranging from sample preparation, chemical treatment with HCl and HF, sieving, slide cover and completion then the counting of 300 particles per sample. The samples yielded sufficient organic residues for detailed palynofacies analysis. The organic constituents observed in the studied samples have been classified into phytoclast, palynomorp and amorphous organic matter groups. The phytoclast group predominates in almost all the sections followed by the palynomorp group with little amount of amorphous organic matter (AOM). The palynofacies parameters used for the study are the continental/ marine and opaque/translucent ratios which led to the construction of the sea-level variation pattern for the formations using Tilia 2.0.2 program.

Two-Experiment Examination of Habitual and Manipulated Foot Placement Angles on the Kinetics, Kinematics, and Muscle Forces of the Barbell Back Squat in Male Lifters.

This two-experiment study aimed to examine the effects of different habitual foot placement angles and also the effects of manipulating the foot placement angle on the kinetics, three-dimensional kinematics and muscle forces of the squat. In experiment 1, seventy lifters completed squats at 70% of their one repetition maximum using a self-preferred placement angle. They were separated based on their habitual foot angle into three groups HIGH, MEDIUM and LOW. In experiment 2, twenty lifters performed squats using the same relative mass in four different foot placement angle conditions (0°, 21°, 42° and control). Three-dimensional kinematics were measured using an eight-camera motion analysis system, ground reaction forces (GRF) using a force platform, and muscle forces using musculoskeletal modelling techniques. In experiment 1, the impulse of the medial GRF, in the descent and ascent phases, was significantly greater in the HIGH group compared to LOW, and in experiment 2 statistically greater in the 42° compared to the 21°, 0° and control conditions. Experiment 2 showed that the control condition statistically increased quadriceps muscle forces in relation to 0°, whereas the 0° condition significantly enhanced gluteus maximus, gastrocnemius and soleus forces compared to control. In experiment 1, patellofemoral joint stress was significantly greater in the HIGH group compared to LOW, and in experiment 2, patellar and patellofemoral loading were statistically greater in the control compared to the 42°, 21°, 0° and control conditions. Owing to the greater medial GRF’s, increased foot placement angles may improve physical preparedness for sprint performance and rapid changes of direction. Reducing the foot angle may attenuate the biomechanical mechanisms linked to the aetiology of knee pathologies and to promote gluteus maximus, gastrocnemius and soleus muscular development. As such, though there does not appear to be an optimal foot placement angle, the observations from this study can be utilised by both strength and conditioning and sports therapy practitioners seeking to maximise training and rehabilitative adaptations.

Chasing Flies: The Use of Wingbeat Frequency as a Communication Cue in Calyptrate Flies (Diptera: Calyptratae).

Simple SummarySome of the fastest and most agile flying insects are the calyptrate flies which include blow flies, flesh flies, and house flies. The current study compared the wingbeat frequency of four species, representing four genera of these flies, recorded in free flight and analyzed using sound editor and analysis software. Wingbeat frequency was found to differ between the four species and between sexes. Such findings provide insight into how flies are communicating and show promise for the use of wingbeat frequency as a novel methodology to identify fly specimens.The incidental sound produced by the oscillation of insect wings during flight provides an opportunity for species identification. Calyptrate flies include some of the fastest and most agile flying insects, capable of rapid changes in direction and the fast pursuit of conspecifics. This flight pattern makes the continuous and close recording of their wingbeat frequency difficult and limited to confined specimens. Advances in sound editor and analysis software, however, have made it possible to isolate low amplitude sounds using noise reduction and pitch detection algorithms. To explore differences in wingbeat frequency between genera and sex, 40 specimens of three-day old Sarcophaga crassipalpis, Lucilia sericata, Calliphora dubia, and Musca vetustissima were individually recorded in free flight in a temperature-controlled room. Results showed significant differences in wingbeat frequency between the four species and intersexual differences for each species. Discriminant analysis classifying the three carrion flies resulted in 77.5% classified correctly overall, with the correct classification of 82.5% of S. crassipalpis, 60% of C. dubia, and 90% of L. sericata, when both mean wingbeat frequency and sex were included. Intersexual differences were further demonstrated by male flies showing significantly higher variability than females in three of the species. These observed intergeneric and intersexual differences in wingbeat frequency start the discussion on the use of the metric as a communication signal by this taxon. The success of the methodology demonstrated differences at the genus level and encourages the recording of additional species and the use of wingbeat frequency as an identification tool for these flies.

Case Study: Automated Stringer Detection Boosts Drilling Efficiency With Less Downtime

_ Horizontal drilling has evolved over decades to become a trusted well construction technique in mature oil-producing regions. However, many challenges remain in geologically complex drilling environments. One challenging drilling scenario arises when the drill bit encounters hard stringers interbedded within softer formations like sandstone. The sudden change in rock mechanics in moving from the formation to the stringer often results in deflection of the drill bit and a deviation in the well path known as a dogleg. The rapid directional changes caused by doglegs lower drilling efficiency by moving the drilling assembly off its planned path, and sometimes, out of the desired reservoir zone. The static loads generated in a dogleg can damage the bottomhole assembly (BHA) and lead to premature bit wear, shortened run life, higher maintenance costs, and more trips downhole. The curved path also increases the risk of stuck casing or completions strings, which can prevent the well from being completed to planned target depth (TD). An operator of a mature field in the North Sea faced such challenges while drilling multilateral wells through reservoir sections containing hard calcite stringers interspersed in sand formations with low unconfined compressive strength. The operator aimed to keep its lifting costs low by increasing the gross rate of penetration (ROP) through these sections. But the doglegs created at each stringer often required pulling back to perform a costly, time-consuming reaming operation to smooth out the well path and allow drilling to continue to TD. On average, the operator amassed 2.7 hours of invisible lost time (ILT) on reaming for every 3,300 ft (1000 m) drilled and achieved significantly lower gross ROP—both of which increased the operator’s per-well lifting costs above plan. Working with the operator, Baker Hughes developed an automated stringer detection service that would identify stringers earlier than previously possible to minimize local doglegs, reduce reaming time, and efficiently deliver wells to plan. Developing an Early-Warning Stringer Detection Service With operator input, the service provider developed an automated service that provided reliable, consistent, and early stringer detection to guide fast corrective action. The service includes an automated stringer-detection module embedded in an advanced measurement-while-drilling (MWD) sensor sub. The sub contains several dynamic sensors that collect a range of vibration and load measurements. The detection module uses a physics-based algorithm that combines two MWD measurements—tangential acceleration and dynamic torque at the bit—to calculate a value for high-frequency torsional oscillation (HFTO) in the BHA. HFTOs are torsional vibrations with frequencies between 50 Hz and 450 Hz that only occur during bit-rock interactions in hard formations. The distinct change in HFTO response during the transition from soft formations to hard formations makes it a leading indicator for detecting stringers in real time during drilling.

Associations between lower limb eccentric muscle capability and change of direction speed in basketball and tennis players.

BackgroundThe ability to perform a quick and rapid change of direction (CoD) is an important determinant of success in a variety of sports. Previous studies have already highlighted that eccentric strength is a dominant predictor of CoD. However, these studies evaluated eccentric strength through a limited number of outcome measures and used small sample sizes.MethodsA total of 196 athletes participated in the study. The aim of our study was to investigate: (1) the correlation between eccentric outcome measures derived from different tests (Nordic hamstring exercise (NHE), countermovement jump (CMJ) and flywheel (FW) squats), (2) the association between eccentric outcome measures and CoD 90°, CoD 180°; and (3) proportion of explained variance in CoD performance.ResultsVery large associations (r = 0.783, p < 0.001) were observed between peak torque during NHE (NHEPT) and force impulse during the eccentric phase of CMJ (CMJFI). Small to moderate correlations were calculated between peak eccentric force in flywheel squats and peak eccentric force in CMJ (r = 0.220–035, p < 0002). All eccentric CMJ outcome measures and NHEPT were reported as moderate negative associations with both CoD tests. Eccentric measures explained 25.1% of the variance in CoD 90° (CMJPF, NHEPT, F0.125 –peak eccentric force during FW squats with 0.125 kg m2 load), while the same outcome measures explained 37.4% of the variance for CoD 180°.ConclusionOur results suggest that different measures of eccentric strength specifically contribute to CoD performance. Therefore, for successful CoD performance, different aspects of eccentric strength training should be considered in testing and training (maximal eccentric strength, eccentric-concentric actions with fast execution).

Effects of Density Current, Diurnal Heating, and Local Terrain on the Mesoscale Environment Conducive to the Yarnell Hill Fire

The Yarnell Hill Fire, triggered by dry lightning on 28 June 2013, was initiated by hot and dry westerly winds, which rapidly shifted to north-northeast by convective-induced outflows. This sudden wind shift led to the demise of 19 firefighters. This study focuses on the environment and its predictive potential in terms of erratically changing the fire spread. Three numerical sensitivity tests are performed investigating the evolving synoptic-meso-β scale environmental wind flow: (1) deactivating the evaporative cooling, (2) deactivating surface-driven diurnal heating/cooling, and (3) removing the mountain. Results show the strong north-northeasterly wind induced by the density current(s) and the diurnal surface sensible heating played the most significant roles in enhancing the mesoscale environment conducive to the rapid change in the fire spread direction. While the mountain played a less significant role in weakening the magnitude of the airflow affecting the fire, it still had an impact. Additionally, the Hot-Dry-Windy (HDW) index is calculated to determine its predictor role with respect to the atmosphere affecting the fire. The focus is not on feedback from explicit fire heating on the larger environment but rather the role of the environmental physical processes in causing the convectively induced rapid wind shifts.

The Role of the Non-Playing Hand during Topspin Forehand in Table Tennis

Theoretical tutorials and the scientific literature do not provide information on the proper use of the non-playing hand in table tennis. This study aimed to evaluate the course of the movement in the joints of the non-playing limb during a table tennis topspin forehand stroke (played after a backspin ball) and to determine the inter-individual movement variability. The study involved 12 male table tennis players (178.7 ± 5.5 cm, 70.0 ± 6.6 kg, 23 ± 3 y) at a competitive level. The participants performed one topspin forehand as a response to a backspin ball. Kinematics were measured using an Inertial Motion Unit–MR3 myoMuscle Master Edition system. Changes in the angles of the upper limb joints (with particular emphasis on the non-playing hand) during the forehand topspin were analyzed. A novel method of normalized function of variance was used to characterize areas of high/low variability of movement. Most of the movements in the joints of the non-playing limb were performed symmetrically to the playing one, especially in the hitting phase. A rapid change of direction characterizes these movements, just before or during the hitting phase, which may indicate a supportive, ‘driving’ character for these movements. High inter-individual variability for the duration of the entire movement cycle in both limbs was observed; higher in the non-playing limb. This perhaps indicates a greater degree of individualization on the non-playing side.

The effect of ankle supports on lower limb biomechanics during functional tasks: A systematic review with meta-analysis

Background: Ankle sprains are common in the athletic population, and are costly for patients in terms of healthcare use. Ankle sprains are even more common in sports that require athletes to perform rapid changes in movement and direction. The most prevalent type of ankle sprain is lateral ankle sprain that typically occur in participants during activities such as running, jumping and agility activities. Ankle supports have been widely used in the rehabilitation of ankle sprains as they have proven to be effective in reducing re-injury rates.

Modelling the dynamics of change in the technical skills of young basketball players: The INEX study.

Although technical skills are a prerequisite for success in basketball, little is known about how they develop over time. In this study, we model the trajectories of technical skill development in young basketball players and investigate the effects of training experience, training volume, body composition, maturity status, physical performance, and club characteristics on skill development. A total of 264 male basketballers from five age-cohorts (11 to 15 years of age) were followed consecutively over three years using a mixed-longitudinal design. Technical skills, training experience and volume, basic anthropometrics, body composition, biological maturation and physical performance were assessed bi-annually. A multilevel hierarchical linear model was used for trajectory analysis. Non-linear trends (p < 0.01) were observed in speed shot shooting, control dribble, defensive movement, slalom sprint, and slalom dribble. Being more experienced and physically fitter had a significant (p < 0.05) positive effect on technical skill development; greater fat-free mass negatively affected skills demanding quick running and rapid changes of direction with or without the ball (p < 0.05). Training volume and biological age did not explain differences in technical skill development (p > 0.05). Moreover, belonging to different clubs had no significant influence on the technical skills trajectories of players. Our findings highlight the important role that individual differences play, over and beyond club structure, in developing skills. Findings improve our understanding on how technical skills develop during adolescence through training, growth, and biological maturation.

A record of the lower Mammoth geomagnetic polarity reversal from a marine succession in the Boso Peninsula, central Japan

SUMMARY Palaeomagnetic records from geological archives provide significant information about the nature of geomagnetic polarity reversals; however, there are few detailed palaeomagnetic records of pre-Pleistocene reversals. The lower Mammoth Subchron boundary (late Pliocene) is recorded in a 10-m interval of a marine succession deposited at high accumulation rates (9–66 cm kyr–1) in the Boso Peninsula, central Japan. Here, we report a continuous palaeomagnetic record of the lower, normal to reverse boundary interval of the Mammoth Subchron, including the geomagnetic field direction and relative palaeointensity, with an average temporal resolution of ca. 800 yr. A hybrid method of thermal demagnetization at 200 °C and progressive alternating field demagnetization were used to effectively extract the primary palaeomagnetic component, which is carried by magnetite. The lower Mammoth transition is characterized by palaeomagnetic direction of instability and decay of the relative palaeointensity, and occurred from late Marine Isotope Stage MG3 (3351 ka) to MG2 (3336 ka) or MG1 (3331 ka), spanning 15–20 kyr. Virtual geomagnetic poles (VGPs), calculated from primary palaeomagnetic directions, rapidly rebounded twice from southern latitudes to northern latitudes within the transition. In contrast to the complex lower Mammoth reversal behaviour recorded in the Boso Peninsula succession, records from a lava sequence in O'ahu (Hawai'i) reveal a rebound following a 180° directional change, and those from a marl succession in Sicily (Italy) indicate a single rapid directional change. Diverse geomagnetic field evolution among these three sections is reflected resolution difference among the records likely in combination with an influence of non-axial dipole field.

Epidemiology of Foot and Ankle Injuries in NCAA Jumping Athletes in the United States During 2009-2014

Background:Foot and ankle injuries comprise a significant proportion of all injuries sustained by National Collegiate Athletic Association (NCAA) athletes. In particular, sports that combine jumping and rapid changes in direction are associated with increased lower extremity injuries.Purpose:To describe the epidemiology of foot and ankle injuries in men’s and women’s jumping sports, including NCAA men’s and women’s basketball, women’s volleyball, and women’s gymnastics, during the 2009-2010 through 2013-2014 seasons.Study Design:Descriptive epidemiology study.Methods:Injury-surveillance data were obtained from the NCAA Injury Surveillance Program for the 2009-2010 through 2013-2014 seasons. Injuries were examined by mechanism, activity during injury, and participation restriction time. Injury rates per 1000 athlete-exposures (AEs), injury rate ratios, and risk ratios with 95% CIs were calculated. Reported sex differences were calculated for men’s and women’s basketball. All 95% CIs not containing 1.0 were considered statistically significant.Results:A total of 1136 players sustained foot and ankle injuries (483 male and 653 female) over 612,680 AEs. These injuries resulted in a combined rate of 1.85 per 1000 AEs (95% CI, 1.75-1.97). Ankle sprains were the most common injury (63.7%), with lateral ligamentous complex injuries making up 77.1% of all ankle sprains. The most common foot injury varied based on sport and sex. Ankle injury rates were higher in male versus female basketball players (injury rate ratio, 1.33 [95% CI, 1.13-1.57]), but foot injury rates did not differ. Among basketball and volleyball players, player contact during jumping was the most common injury mechanism. Female gymnasts had higher overuse injury rates than other athletes (0.49/1000 AEs [95% CI, 0.30-0.74]; P < .002). Overall, female basketball players were 1.81 times more likely to sustain an overuse injury than male basketball players (95% CI, 1.02-3.20; P = .02).Conclusion:The most common foot and ankle injury sustained in collegiate jumping sports was a lateral ligamentous complex ankle sprain. Injury-prevention programs focusing on ankle flexibility, strength, and proprioception may help to alleviate the injury burden and lessen severity. Improving the anticipation of contact during jumping and landing may reduce injury rates and increase player safety. The increased prevalence of overuse injuries in female collegiate athletes competing in jumping sports necessitates further investigation to reduce injury rates through prevention and training programs.