Although there are many virtual reality (VR) applications in sports, only a handful of studies visualized the whole body. There is still a lack of understanding, how much of the own body must be ...visualized in the head-mounted display (HMD) based VR, to ensure fidelity and similar performance outcome as in the real-world. In the current study, 20 young and healthy participants completed three tasks in a real and virtual environment: balance task, grasping task, and throwing task with a ball. The aim was to find out the meaning of the visualization of different body parts for the quality of movement execution and to derive future guidelines for virtual body presentation. In addition, a comparison of human performance between reality and VR, with whole-body visualization was made. Focusing on the main goal of the current study, there were differences within the measured parameters due to the visualization of different body parts. In the balance task, the differences within the VR body visualization consisted mainly through no-body visualization (NB) compared to the other visualization types defined as whole-body (WB), WB except feet (NF), as well as WB except feet and legs (NLF). In the grasping task, the different body visualization seemed to have no impact on the participants' performances. In the throwing task, the whole-body visualization led to higher accuracy compared to the other visualization types. Regarding the comparison between the conditions, we found significant differences between reality and VR, which had a large effect on the parameters time for completion in the balance and grasping task, the number of foot strikes on the beam in the balance task, as well as the subjective estimation of the difficulty for all tasks. However, the number of errors and the quality of the performances did not differ significantly. The current study was the first study comparing sports-related tasks in VR and reality with further manipulations (occlusions of body parts) of the virtual body. For studies analyzing perception and sports performance or for VR sports interventions, we recommend the visualization of the whole body in real-time.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
For realistic and reliable full-body visualization in virtual reality, the HTC VIVE Tracker could be an alternative to highly complex and cost- and effort-intensive motion capture systems such as ...Vicon. Due to its lighter weight and smaller dimensions, the latest generation of trackers is proving to be very promising for capturing human movements. The aim of this study was to investigate the accuracy of the HTC VIVE Tracker 3.0 compared to the gold-standard Vicon for different arrangements of the base stations and various velocities during an athletic movement. Therefore, the position data from three trackers attached to the hip, knee and ankle of one sporty participant were recorded while riding a bicycle ergometer at different pedaling frequencies and different base station arrangements. As parameters for the measurement accuracy, the trajectories of the linear motion of the knee and the circular motion of the ankle were compared between VIVE and Vicon by calculating the spatial distance from the raw data at each point in time. Both the pedaling frequency and the arrangement of the base stations significantly affected the measurement accuracy, with the lowest pedaling frequency of 80 rpm and the rectangular arrangement recommended by the manufacturer showing the smallest spatial differences of 10.4 mm ± 4.5 mm at the knee and 11.3 mm ± 5.1 mm at the ankle. As the pedaling frequency increased gradually (120 rpm and 160 rpm), the measurement accuracy of the trackers per step decreased less at the knee (approximately 5 mm) than at the ankle (approximately 10 mm). In conclusion, the measurement accuracy for various athletic skills was high enough to enable the visualization of body limbs or the entire body using inverse kinematics in VR on the one hand and, on the other hand, to provide initial insights into the quality of certain techniques at lower speeds in sports science research. However, the VIVE trackers are not suitable for exact biomechanical analyses.
We investigated, in depth, the interrelations among structure, magnetic properties, relaxation dynamics and magnetic hyperthermia performance of magnetic nanoflowers. The nanoflowers are about 39 nm ...in size, and consist of densely packed iron oxide cores. They display a remanent magnetization, which we explain by the exchange coupling between the cores, but we observe indications for internal spin disorder. By polarized small-angle neutron scattering, we unambiguously confirm that, on average, the nanoflowers are preferentially magnetized along one direction. The extracted discrete relaxation time distribution of the colloidally dispersed particles indicates the presence of three distinct relaxation contributions. We can explain the two slower processes by Brownian and classical Néel relaxation, respectively. The additionally observed very fast relaxation contributions are attributed by us to the relaxation of disordered spins within the nanoflowers. Finally, we show that the intrinsic loss power (ILP, magnetic hyperthermia performance) of the nanoflowers measured in colloidal dispersion at high frequency is comparatively large and independent of the viscosity of the surrounding medium. This concurs with our assumption that the observed relaxation in the high frequency range is primarily a result of internal spin relaxation, and possibly connected to the disordered spins within the individual nanoflowers.
Visual anticipation is essential for performance in sports. This review provides information on the differences between stimulus presentations and motor responses in eye-tracking studies and ...considers virtual reality (VR), a new possibility to present stimuli. A systematic literature search on PubMed, ScienceDirect, IEEE Xplore, and SURF was conducted. The number of studies examining the influence of stimulus presentation (in situ, video) is deficient but still sufficient to describe differences in gaze behavior. The seven reviewed studies indicate that stimulus presentations can cause differences in gaze behavior. Further research should focus on displaying game situations via VR. The advantages of a scientific approach using VR are experimental control and repeatability. In addition, game situations could be standardized and movement responses could be included in the analysis.
Virtual reality (VR) has become a common tool and is often considered for sport-specific purposes. Despite the increased usage, the transfer of VR-adapted skills into the real-world (RW) has not yet ...been sufficiently studied, and it is still unknown how much of the own body must be visible to complete motoric tasks within VR. In addition, it should be clarified whether older adults also need to perceive their body within VR scenarios to the same extent as younger people extending the usability. Therefore, younger (18-30 years old) and elderly adults (55 years and older) were tested (n = 42) performing a balance-, grasping- and throwing task in VR (HMD based) accompanied with different body visualization types in VR and in the RW having the regular visual input of body's components. Comparing the performances between the age groups, the time for completion, the number of steps (balance task), the subjective estimation of difficulty, the number of errors, and a rating system revealing movements' quality were considered as examined parameters. A one-way ANOVA/Friedmann with repeated measurements with factor body visualization was conducted to test the influence of varying body visualizations during task completion. Comparisons between the conditions RW, VR were performed using the t-Tests/Wilcoxon tests, and to compare both age groups young, old, t-Tests for independent samples/Mann-Whitney-U-Test were used. The analyses of the effect of body visualization on performances showed a significant loss in movement's quality when no body part was visualized (p < .05). This did not occur for the elderly adults, for which no influence of the body visualization on their performance could be proven. Comparing both age groups, the elderly adults performed significantly worse than the young age group in both conditions (p < .05). In VR, both groups showed longer times for completion, a higher rating of tasks' difficulty in the balance and throwing task, and less performance quality in the grasping task. Overall, the results suggest using VR for the elderly with caution to the task demands, and the visualization of the body seemed less crucial for generating task completion. In summary, the actual task demands in VR could be successfully performed by elderly adults, even once one has to reckon with losses within movement's quality. Although more different movements should be tested, basic elements are also realizable for elderly adults expanding possible areas of VR applications.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Virtual reality is increasingly applied to support physical training and improve athletes’ performance in sports. Nevertheless, there is a research deficit in that, especially in martial arts, it has ...not yet been shown to what extent the response behavior of athletes in virtual reality is the same as in the real world. If this can be confirmed, a transfer of VR-adapted skills to RW can be expected and sports training in a virtual environment can be applied to improve sports performance. Since the response behavior is essential for many sports, this study compares it in karate kumite to the competition-important attack (Kizami-Zuki) of a real and a virtual opponent. Experienced karate athletes wore a head-mounted display and were asked to respond quickly and efficiently to 22 karate attacks, of which eight were Kizami Zuki’s attacks. Using a video-based movement assessment, karate experts quantified the response behavior with the parameters ‘time for response’, ‘response quality’ and ‘kind of response’. Results show no significant differences in ‘time for response’ and ‘kind of response’ between both conditions (virtual reality vs. real world). Only the ‘response quality’ was rated better in real world than in virtual reality. It is concluded that the ‘time of response’ and ‘kind of response’ for karate kumite athletes in virtual reality are similar to that in the real world.
Virtual reality (VR) is popular across many fields and is increasingly used in sports as a training tool. The reason, therefore, is recently improved display technologies, more powerful computation ...capacity, and lower costs of head-mounted displays for VR. As in the real-world (R), visual effects are the most important stimulus provided by VR. However, it has not been demonstrated whether the gaze behavior would achieve the same level in VR as in R. This information will be important for the development of applications or software in VR. Therefore, several tasks were designed to analyze the gaze accuracy and gaze precision using eye-tracking devices in R and VR. 21 participants conducted three eye-movement tasks in sequence: gaze at static targets, tracking a moving target, and gaze at targets at different distances. To analyze the data, an averaged distance with root mean square was calculated between the coordinates of each target and the recorded gaze points for each task. In gaze accuracy, the results showed no significant differences between R and VR in gaze at static targets (1 m distance,
p
> 0.05) and small significant differences at targets placed at different distances (
p
< 0.05), as well as large differences in tracking the moving target (
p
< 0.05). The precision in VR is significantly worse compared to R in all tasks with static gaze targets (
p
< 0.05). On the whole, this study gives a first insight into comparing foveal vision, especially gaze accuracy and precision between R and VR, and can, therefore, serve as a reference for the development of VR applications in the future.
This pioneering study presents an in-depth biomechanical examinations of soccer’s diving header, aiming to quantify its impact on ball speed enhancement (BSE) and effective offensive range (EOR). ...Despite the diving header’s widespread acclaim and historical significance, there remains a dearth of scientific scrutiny into its biomechanical intricacies. Employing an innovative research design featuring a static hanging ball at varied offensive distances and heights, this study replicates diverse header scenarios. The results of 3D motion quantification have shown that a physically excellent player (identified through the maximal standing long jump test) could reach an EOR around 2.64 times his body height. Furthermore, this study unveils that proficient players could attain BSE surpassing 9 m/s, signifying the diving header’s heightened efficacy compared to traditional heading techniques, which could only result in 4.5 m/s. Correlation analyses unveil noteworthy relationships, highlighting the pivotal role of head speed at impact and the influence of minimizing speed drop and temporal disparities for amplified effectiveness. Considerations for optimizing diving header execution are introduced, emphasizing the necessity for targeted training programs. Despite acknowledged limitations inherent to its pilot nature, this exploration furnishes foundational knowledge to guide subsequent research and practical applications, providing valuable insights into soccer training and skill development through a biomechanical lens.
Since the mechanism of the synthesis of magnetite from a stoichiometric mixture of hematite and iron is still under debate, systematic studies of the phase transformations in such powder mixture ...processed under field assisted sintering conditions, are presented. Phase contributions, grain sizes and stoichiometries of the sintered composites were determined using scanning electron microscopy, high energy X-ray diffraction and Mößbauer spectroscopy. It was shown that with an increasing sintering temperature an accelerated growth of magnetite can be observed, while the amount of hematite decreases. Additionally, intermediate wustite phase was observed with a maximum intensity where iron vanished from the samples. Therefore, it was concluded that the transition from hematite - iron mixture to magnetite actually takes place in two steps. In the first step, iron reduces hematite to magnetite and oxidizes itself to wustite. In the second step, wustite enables the nucleation of magnetite and with the help of hematite it transforms into nearly pure stoichiometric magnetite at higher sintering temperatures. In composites sintered from pure hematite under the same conditions only a minor transition to highly nonstoichiometric magnetite was observed emphasizing the above mentioned route of transformation.
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•Phase transformation of hematite and iron in FAST was investigated.•Hematite and iron transform into magnetite.•First, iron oxides to wustite while hematite reduces partially to magnetite.•Second, wustite and hematite form together pure magnetite.•The obtained magnetite is highly stoichiometric (Fe2.982O4).
CaTiO
is a promising candidate as a pseudo-piezoelectric scaffold material for bone implantation. In this study, pure and magnesium/iron doped CaTiO
are synthesized by sol-gel method and spark plasma ...sintering. Energy dispersive X-ray mapping confirm the homogenous distribution of doping elements in sintered samples. High-energy X-ray diffraction investigations reveal that doping of nanostructured CaTiO
increased the strain and defects in the structure of CaTiO
compared to the pure one. This led to a stronger pseudo-piezoelectric effect in the doped samples. The charge produced in magnesium doped CaTiO
due to the direct piezoelectric effect is (2.9 ± 0.1) pC which was larger than the one produced in pure CaTiO
(2.1 ± 0.3) pC, whereas the maximum charge was generated by iron doped CaTiO
with (3.6 ± 0.2) pC. Therefore, the pseudo-piezoelectric behavior can be tuned by doping. This tuning of pseudo-piezoelectric response provides the possibility to systematically study the bone response using different piezoelectric strengths and possibly adjust for bone tissue engineering.
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