Objective: This study aimed to compare young female kendo athletes and sex-matched non-athlete controls to determine if there are differences in handgrip strength between the groups, and if so, at what age these differences appear. Methods: Thirty-three female kendo athletes (mean age [SD]: 9.5 [1.8] years) and 33 sex-matched female non-athlete controls (mean age [SD]: 9.3 [1.8] years) between the ages of 6 and 12 years participated in this study. Handgrip strength was measured using a Smedley dynamometer, and the average value of both hands was used for analysis. The kendo experience was determined when they started practice. Handgrip strength was compared between groups. Statistical moderation was used to determine if the relationship between group and handgrip strength depended upon the age of the participant. Results: Female kendo athletes exhibited significantly higher handgrip strength compared to female non-athlete controls both before (4.5 kg [95% CI: 1.9, 7.03]) and after (2.4 kg [95% CI: 0.7, 3.9]) adjusting for body mass. Adjusting for body mass, we observed that the relationship between group and handgrip strength depended on the child's age (group Å~ age, t = 2.75, p = 0.007). Using the Johnson-Neyman procedure, we identified statistically significant differences between groups starting from 8.3 years old and above. Without adjusting for body mass, significant differences appeared from 8.0 years old and above. Below that age, differences between groups were minimal and not statistically different. Conclusion: Our findings suggest that sports (e.g., kendo) requiring grasping equipment with the hands may help improve handgrip strength in adulthood.

Objectives: Novel three-dimensional (3D) motion analysis methods using omnidirectional cameras are developed and a new framework is presented to integrate this analysis with immersive Virtual Reality (VR) motion feedback. This study addresses the limitations of sports motion analysis that relies on narrow-field-of-view conventional cameras. Design: Employing a novel methodological and experimental design, new mathematical operations tailored to the spherical projection of omnidirectional cameras were developed and validated. Subsequently, the dual application of the design was demonstrated in quantitative analysis and experiential feedback. Methods: New 3D reconstruction algorithms, inspired by the Direct Linear Transformation (DLT) and Non-Linear Transformation (NLT) principles but adapted for omnidirectional imagery, were developed. These methods utilize the longitude and latitude of celestial sphere images to determine the camera ray direction, thereby enabling the determination of the camera position/orientation (DLT-inspired method) or the relative position/orientation of the cameras (NLT-inspired method). A separate purely geometric method for minimal-calibration 2D position determination using two omnidirectional cameras was also proposed. Omnidirectional imagery data were then used to generate immersive 360° VR content for motion feedback using a Head-Mounted Display (HMD). Results: The DLT-inspired 3D reconstruction method achieved an error of 0.22% relative to the calibrated space volume, and the NLT-inspired method achieved an error of 0.34%, both comparable to the accuracy of the gold standard methods. These methods drastically reduce the required number of cameras and technical complexity. Furthermore, omnidirectional recordings were successfully transformed into immersive VR content, enabling an embodied re-experience of movement. Conclusions: Omnidirectional cameras have successfully overcome the field-of-view and complexity limitations of traditional DLT/NLT methods, achieving high-accuracy 3D motion analysis with minimal camera units. The integration of this precise analysis with immersive VR motion feedback results in a powerful, unified framework that accelerates motor-skill acquisition and performance enhancement. Thus, this study paves the way for the next generation of real-time mobile motion intelligence systems in sports science.

The regular participation in physical activity through resistance and endurance type exercise is associated with improvements in multiple physiological systems and is associated with improvement in markers of health. There are well established fitness principles for increasing aerobic capacity, muscular strength, muscular size, endurance, etc. The effectiveness of exercise protocols is sometimes judged based on whether the protocols are capable of improving those aforementioned outcomes. What is less discussed is whether it is necessary to emphasize “improvement” when the goal is maximizing the health span. Objectives: To discuss whether there is a reason to progress beyond the minimum guidelines when the goal is health. Design and Methods: Narrative Review. Results: A review of recent papers on physical activity provide a compelling case for the importance of physical activity for reducing morbidity and premature mortality. It is clear that doing even a little bit of physical activity is likely to be beneficial for health. Some work has also found additional improvement beyond the minimum recommended guidelines. Conclusions: Meeting the guidelines for physical activity is associated with numerous beneficial health outcomes. The ultimate goal is for individuals to maintain sufficient amounts of physical activity across their entire life span. For some, pushing themselves in exercise could be the motivation they need to maintain an exercise protocol for decades. For others, always having to push the boundaries is a deterrent and the goal could be to focus on achieving participation in the behavior rather than a focus on some change in outcome (e.g. strength).