Reaction forces and bone maturation in taekwondo: comparison with and without tatami

Childbirth-related injuries are one of the main causes of pelvic floor dysfunction. To attempt to avoid serious tears during delivery, an episiotomy can be performed. In this study, we intended to investigate the biomechanical performance of the pelvic floor muscles after performing different episiotomies using a physics-based computational model which includes the pelvic floor muscles and the fetus. Previous biomechanical studies have analysed the mechanical effects of single incisions of different lengths; in this study, we intend to analyse the implications of multiple small incisions, evaluating the reaction forces, the stress on the muscles and the loss of tissue integrity sustained by the pelvic floor. The obtained results predict that an episiotomy delivery reduces the likelihood of macroscopic levator trauma by decreasing the stress on the region of insertion of the rectal area of the levator ani in the symphysis pubis . From the mechanical point of view, multiple incisions do not bring benefits compared to larger incisions. However, nothing can be ascertained about the clinical benefit of such an approach.

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Running ground reaction forces across footwear conditions are predicted from the motion of two body mass components

Journal of Applied Physiology ◽

10.1152/japplphysiol.00925.2018 ◽

2019 ◽

Vol 126 (5) ◽

pp. 1315-1325 ◽

Cited By ~ 3

Author(s):

Andrew B. Udofa ◽

Kenneth P. Clark ◽

Laurence J. Ryan ◽

Peter G. Weyand

Keyword(s):

Ground Reaction Force ◽

Lower Limb ◽

Reaction Force ◽

Ground Reaction Forces ◽

Vertical Ground Reaction Force ◽

Time Patterns ◽

Foot Strike ◽

Reaction Forces ◽

Vertical Ground ◽

Force Time

Although running shoes alter foot-ground reaction forces, particularly during impact, how they do so is incompletely understood. Here, we hypothesized that footwear effects on running ground reaction force-time patterns can be accurately predicted from the motion of two components of the body’s mass (mb): the contacting lower-limb (m1 = 0.08mb) and the remainder (m2 = 0.92mb). Simultaneous motion and vertical ground reaction force-time data were acquired at 1,000 Hz from eight uninstructed subjects running on a force-instrumented treadmill at 4.0 and 7.0 m/s under four footwear conditions: barefoot, minimal sole, thin sole, and thick sole. Vertical ground reaction force-time patterns were generated from the two-mass model using body mass and footfall-specific measures of contact time, aerial time, and lower-limb impact deceleration. Model force-time patterns generated using the empirical inputs acquired for each footfall matched the measured patterns closely across the four footwear conditions at both protocol speeds ( r2 = 0.96 ± 0.004; root mean squared error = 0.17 ± 0.01 body-weight units; n = 275 total footfalls). Foot landing angles (θF) were inversely related to footwear thickness; more positive or plantar-flexed landing angles coincided with longer-impact durations and force-time patterns lacking distinct rising-edge force peaks. Our results support three conclusions: 1) running ground reaction force-time patterns across footwear conditions can be accurately predicted using our two-mass, two-impulse model, 2) impact forces, regardless of foot strike mechanics, can be accurately quantified from lower-limb motion and a fixed anatomical mass (0.08mb), and 3) runners maintain similar loading rates (ΔFvertical/Δtime) across footwear conditions by altering foot strike angle to regulate the duration of impact. NEW & NOTEWORTHY Here, we validate a two-mass, two-impulse model of running vertical ground reaction forces across four footwear thickness conditions (barefoot, minimal, thin, thick). Our model allows the impact portion of the impulse to be extracted from measured total ground reaction force-time patterns using motion data from the ankle. The gait adjustments observed across footwear conditions revealed that runners maintained similar loading rates across footwear conditions by altering foot strike angles to regulate the duration of impact.

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Effect of guide rail profile errors on the motion accuracy for a heavy-duty hydrostatic turntable

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406219845406 ◽

2019 ◽

Vol 233 (15) ◽

pp. 5350-5362 ◽

Cited By ~ 1

Author(s):

Yongsheng Zhao ◽

Hongchao Wu ◽

Congbin Yang ◽

Ligang Cai ◽

Zhifeng Liu

Keyword(s):

Machine Tool ◽

Reynolds Equation ◽

Machining Accuracy ◽

Guide Rail ◽

Heavy Duty ◽

Motion Equations ◽

Rotating Speed ◽

Proposed Model ◽

Reaction Forces ◽

Profile Errors

The motion accuracy of hydrostatic turntable is the key in improving the machining accuracy of heavy-duty machine tool. However, the motion accuracy of hydrostatic turntable depends not only on the offset load but also on the rotating speed of the turntable as well as the profile errors of the guide rails. In this paper, a simulation model is developed to analyze the effect of guide rail profile errors on the motion accuracy of hydrostatic turntable. The reaction forces of preload thrust bearing and hydrostatic circular oil pads are obtained based on the Reynolds equation of the lubricant film. The motion equations of hydrostatic turntable are derived in which the profile errors of two guide rails are considered. The results show that the motion accuracy of hydrostatic turntable can be affected by wavelength, amplitude of profile errors and speed, and offset load of turntable. Finally, the motion accuracy of heavy-duty hydrostatic turntable used in XCKA28105 type turning and milling composite machine tool is obtained by using the presented method. Comparing with the experimental results, the proposed model can be used to predict the machining accuracy caused by the profile errors of guide rails for any heavy-duty hydrostatic turntable.

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Horizon radiation reaction forces

Journal of High Energy Physics ◽

10.1007/jhep10(2020)026 ◽

2020 ◽

Vol 2020 (10) ◽

Author(s):

Walter D. Goldberger ◽

Ira Z. Rothstein

Keyword(s):

Black Hole ◽

Equations Of Motion ◽

Finite Size ◽

Radiation Reaction ◽

Effective Field ◽

Compact Objects ◽

Finite Size Effect ◽

Binary Black Holes ◽

Dissipative Effects ◽

Reaction Forces

Abstract Using Effective Field Theory (EFT) methods, we compute the effects of horizon dissipation on the gravitational interactions of relativistic binary black hole systems. We assume that the dynamics is perturbative, i.e it admits an expansion in powers of Newton’s constant (post-Minkowskian, or PM, approximation). As applications, we compute corrections to the scattering angle in a black hole collision due to dissipative effects to leading PM order, as well as the post-Newtonian (PN) corrections to the equations of motion of binary black holes in non-relativistic orbits, which represents the leading order finite size effect in the equations of motion. The methods developed here are also applicable to the case of more general compact objects, eg. neutron stars, where the magnitude of the dissipative effects depends on non-gravitational physics (e.g, the equation of state for nuclear matter).

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A Bio-Inspired Compliance Planning and Implementation Method for Hydraulically Actuated Quadruped Robots with Consideration of Ground Stiffness

Sensors ◽

10.3390/s21082838 ◽

2021 ◽

Vol 21 (8) ◽

pp. 2838

Author(s):

Xiaoxing Zhang ◽

Haoyuan Yi ◽

Junjun Liu ◽

Qi Li ◽

Xin Luo

Keyword(s):

Harmonic Oscillation ◽

Ground Surface ◽

Legged Locomotion ◽

Soft Ground ◽

Quadruped Robots ◽

In Series ◽

Reaction Forces ◽

Implementation Method ◽

The Stability ◽

Natural Dynamics

There has been a rising interest in compliant legged locomotion to improve the adaptability and energy efficiency of robots. However, few approaches can be generalized to soft ground due to the lack of consideration of the ground surface. When a robot locomotes on soft ground, the elastic robot legs and compressible ground surface are connected in series. The combined compliance of the leg and surface determines the natural dynamics of the whole system and affects the stability and efficiency of the robot. This paper proposes a bio-inspired leg compliance planning and implementation method with consideration of the ground surface. The ground stiffness is estimated based on analysis of ground reaction forces in the frequency domain, and the leg compliance is actively regulated during locomotion, adapting them to achieve harmonic oscillation. The leg compliance is planned on the condition of resonant movement which agrees with natural dynamics and facilitates rhythmicity and efficiency. The proposed method has been implemented on a hydraulic quadruped robot. The simulations and experimental results verified the effectiveness of our method.

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Estimation of Ground Reaction Forces Based on Knee Joint Acceleration of Lower-Limb Exoskeletons

2020 International Automatic Control Conference (CACS) ◽

10.1109/cacs50047.2020.9289732 ◽

2020 ◽

Author(s):

Tesheng Hsiao ◽

Kinglam Yip ◽

Yun-Jen Chiu

Keyword(s):

Knee Joint ◽

Lower Limb ◽

Ground Reaction Forces ◽

Reaction Forces ◽

Joint Acceleration

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Ground Reaction Forces of Dressage Horses Performing the Piaffe

Animals ◽

10.3390/ani11020436 ◽

2021 ◽

Vol 11 (2) ◽

pp. 436 ◽

Cited By ~ 1

Author(s):

Hilary Mary Clayton ◽

Sarah Jane Hobbs

Keyword(s):

Coefficient Of Variation ◽

Three Dimensional ◽

Individual Variability ◽

The Other ◽

Ground Reaction Forces ◽

High Coefficient ◽

Reaction Forces

The piaffe is an artificial, diagonally coordinated movement performed in the highest levels of dressage competition. The ground reaction forces (GRFs) of horses performing the piaffe do not appear to have been reported. Therefore, the objective of this study was to describe three-dimensional GRFs in ridden dressage horses performing the piaffe. In-ground force plates were used to capture fore and hindlimb GRF data from seven well-trained dressage horses. Peak vertical GRF was significantly higher in forelimbs than in the hindlimbs (7.39 ± 0.99 N/kg vs. 6.41 ± 0.64 N/kg; p < 0.001) with vertical impulse showing a trend toward higher forelimb values. Peak longitudinal forces were small with no difference in the magnitude of braking or propulsive forces between fore and hindlimbs. Peak transverse forces were similar in magnitude to longitudinal forces and were mostly directed medially in the hindlimbs. Both the intra- and inter-individual variability of longitudinal and transverse GRFs were high (coefficient of variation 25–68%). Compared with the other diagonal gaits of dressage horses, the vertical GRF somewhat shifted toward the hindlimbs. The high step-to-step variability of the horizontal GRF components is thought to reflect the challenge of balancing on one diagonal pair of limbs with no forward momentum.

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Injuries in Collegiate Track and Field Jumping: A 2-Year Prospective Surveillance Study

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967120973397 ◽

2021 ◽

Vol 9 (1) ◽

pp. 232596712097339

Author(s):

Shota Enoki ◽

Mami Nagao ◽

Soju Ishimatsu ◽

Takuya Shimizu ◽

Rieko Kuramochi

Keyword(s):

Track And Field ◽

Flexor Hallucis Longus ◽

Injury Incidence ◽

Hamstring Strain ◽

Muscle Rupture ◽

Baseline Information ◽

Long Jump ◽

Reaction Forces ◽

Pole Vault ◽

Type Of Injury

Background: Athletes participating in track and field jumping events (long jump, triple jump, high jump, and pole vault) are exposed to ground-reaction forces on the takeoff leg that are several times their body weight. This can cause injuries specific to such activities. Purpose: To determine the incidence of injuries in collegiate jumpers using the guidelines set forth by a 2014 consensus statement on injury surveillance during track and field events. Study Design: Descriptive epidemiology study. Methods: A total of 51 jumpers between April 2016 and March 2017 and 54 jumpers between April 2017 and March 2018 participated in this study. All athletes were from a single college in Japan. Baseline information on athletes participating in the long jump, triple jump, high jump, and pole vault was collected at study enrollment. Practice and competition exposures were reported by the team trainer. Injury incidence was calculated as the number of injuries per 1000 athlete-exposures (AEs). Results: A total of 147 injuries were reported among 16,998 exposures (8.65 injuries per 1000 AEs). The most common injury locations were the posterior thigh and lateral ankle (17.0%), followed by the posterior foot or toe (12.9%); the most frequent type of injury was strain/muscle rupture/tear (21.1%). The most common injury for long jumpers was ankle sprain (23.3%); for high jumpers, flexor hallucis longus tendinosis (15.8%); and for pole vaulters, hamstring strain (13.2%). Conclusion: The overall characteristics are different for each event; therefore, injuries for each event need to be investigated.

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