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1.
Adv Exp Med Biol ; 1232: 339-345, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31893429

RESUMO

We used a miniature broadband NIRS system to monitor concentration changes in brain oxygenation (oxy- and deoxy- haemoglobin [HbO2], [HHb]) and oxidised cytochrome-c-oxidase ([oxCCO]) during a high +Gz acceleration, induced by a human centrifuge, on two healthy experienced volunteers (2 male, 34 and 37 years). We performed a sequence of several +Gz exposures that were terminated at the onset of visual symptoms (loss of peripheral vision). Systemic parameters were recorded (i.e. heart rate, blood pressure and arterial saturation), and brain tissue blood volume changes ([HbT] = [HbO2] + [HHb]) and oxygen delivery ([HbDiff] = [HbO2] - [HHb]) were calculated. Volunteer 1 demonstrated a decrease in [HbT] of -3.49 ± 0.02 µMol and [HbDiff] of -3.23 ± 0.44 µMol, and an increase of [oxCCO] of 0.42 ± 0.01µMol. Volunteer 2 demonstrated a decrease in [HbDiff] of -4.37 ± 0.23 µMol, and no significant change in [HbT] (0.53 ± 0.06 µMol) and [oxCCO] (0.09 ± 0.06 µMol). The variability of the brain metabolic response was related to the level of ischaemia, suggesting that suppression of metabolism was due to lack of glucose substrate delivery rather than oxygen availability.


Assuntos
Aceleração , Complexo IV da Cadeia de Transporte de Elétrons , Hemodinâmica , Espectroscopia de Luz Próxima ao Infravermelho , Adulto , Encéfalo/enzimologia , Encéfalo/metabolismo , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Voluntários Saudáveis , Humanos , Masculino , Estresse Oxidativo , Oximetria/instrumentação , Oxigênio/metabolismo
2.
J Sports Sci ; 38(3): 336-342, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31795818

RESUMO

A decrease in speed when sprinting on the bend compared with the straight has been attributed to kinetic, kinematic and spatiotemporal modifications. Although maximal speed is dependent on an athlete's ability to accelerate, there is limited research investigating the acceleration phase of bend sprinting. This study used a lower limb and trunk marker set with 15 optoelectronic cameras to examine kinematic and spatiotemporal variables of the lower limb during sprinting on the bend and straight. Nine sprinters completed up to six 30 m maximal effort trials in bend (radius 36.5 m, lane one) and straight conditions. An increase in body lateral lean at touchdown resulted in a number of asymmetric kinematic modifications. Whilst the left limb demonstrated a greater peak hip adduction, peak hip internal rotation and peak ankle eversion on the bend compared with the straight, the right limb was characterised by an increase in peak hip abduction. These results demonstrate that kinematic modifications start early in the race and likely accumulate, resulting in greater modifications at maximal speed. It is recommended that strength and conditioning programmes target the hip, ankle and foot in the non-sagittal planes. In addition, sprint training should prioritise specificity by occurring on the bend.


Assuntos
Extremidade Inferior/fisiologia , Corrida/fisiologia , Atletismo/fisiologia , Aceleração , Tornozelo/fisiologia , Fenômenos Biomecânicos , Pé/fisiologia , Quadril/fisiologia , Humanos , Joelho/fisiologia , Postura/fisiologia , Rotação , Estudos de Tempo e Movimento , Adulto Jovem
3.
J Sports Sci ; 38(3): 343-350, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31809646

RESUMO

Resolving intra-stride accelerations from training and game data routinely collected by athlete tracking devices is rarely attempted, even though these data can provide important insights into the physical condition of athletes. This study describes in detail a novel analysis tool which uses accelerometer-based measures of step variability to assess longitudinal consistency of stride technique. The performance of the analysis tool was examined by combining results from the analysis of data collected over the course of an Australian Football League season with instances of missed or modified training. Results demonstrated increased gait-related trunk acceleration variability when training was modified due to load or accumulated game and training activity (p = 0.02) and reduced trunk acceleration variability in the week following a training modification due to any injury described as "ankle", "heel", or any other description that would loosely refer to a joint or bone in the leg (p = 0.01). These results support the findings of recent research which used a slightly modified version of the same analysis tool to demonstrate an increase in gait-related trunk acceleration variability with the increased acute physical load.


Assuntos
Acelerometria/instrumentação , Monitores de Aptidão Física , Análise da Marcha , Perna (Membro)/fisiologia , Corrida/fisiologia , Futebol/fisiologia , Aceleração , Adulto , Austrália , Fenômenos Biomecânicos , Comportamento Competitivo/fisiologia , Sistemas de Informação Geográfica , Humanos , Masculino , Movimento/fisiologia , Condicionamento Físico Humano/fisiologia , Tronco/fisiologia , Adulto Jovem
4.
J Sports Sci ; 38(1): 29-37, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31631783

RESUMO

This study investigated the role of reactive and eccentric strength in stiffness regulation during maximum velocity sprinting (Vmax) in team sport athletes compared with highly trained sprinters. Thirteen team sport athletes and eleven highly trained sprinters were recruited. Vmax was measured using radar, and stiffness regulation was inferred from modelled vertical and leg spring stiffness. Reactive strength (RSI) was determined from a 0.50 m drop jump, and an eccentric back squat was used to assess maximum isoinertial eccentric force. Trained sprinters attained a higher Vmax than team sport athletes, partly due to a briefer contact time and higher vertical stiffness. Trained sprinters exhibited a moderately higher RSI via the attainment of a briefer and more forceful ground contact phase, while RSI also demonstrated large to very large associations with vertical stiffness and Vmax, respectively. Isoinertial eccentric force was largely correlated with Vmax, but only moderately correlated with vertical stiffness. Reactive and eccentric strength contribute to the ability to regulate leg spring stiffness at Vmax, and subsequently, the attainment of faster sprinting speeds in highly trained sprinters versus team sport athletes. However, stiffness regulation appears to be a task-specific neuromuscular skill, reinforcing the importance of specificity in the development of sprint performance.


Assuntos
Desempenho Atlético/fisiologia , Extremidade Inferior/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Condicionamento Físico Humano , Corrida/fisiologia , Aceleração , Adulto , Fenômenos Biomecânicos , Estudos Transversais , Feminino , Humanos , Masculino , Adulto Jovem
5.
J Sports Sci ; 38(1): 53-61, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31623521

RESUMO

This study aimed 1) to examine the validity of inertial measurement unit (IMU)-based hip flexion strength test, and 2) to investigate the hip flexion strength test as an indicator of sprint performance. Eight males performed five repeated hip flexion-extension, while leg motion was recorded using an IMU and a motion capture system (Mocap). As the second experiment, 24 male athletes performed the IMU-based hip flexion strength test and sprinted 50 m, during which step-to-step ground reaction force (GRF) was recorded. The strength test variables were calculated using IMU and Mocap data including angular impulse, mean moment, and positive and negative work and power. Using GRF data, step-to-step spatiotemporal variables were obtained. The results showed high intra-class correlation coefficient and correlation coefficient (both >0.909) between IMU and Mocap for angular impulse, mean moment, positive work and power. The hip flexion mean moment showed significant correlation with running speed from the 5th-8th step section onwards. The angular impulse, mean moment, positive work and power are recommended to be used for the IMU-based hip flexion strength test variables in terms of accuracy and validity. Moreover, the proposed IMU-based hip flexion strength test can be an indicator for better sprinting performance.


Assuntos
Desempenho Atlético/fisiologia , Teste de Esforço/métodos , Quadril/fisiologia , Força Muscular/fisiologia , Corrida/fisiologia , Aceleração , Adulto , Fenômenos Biomecânicos , Humanos , Masculino , Reprodutibilidade dos Testes , Estudos de Tempo e Movimento , Adulto Jovem
6.
J Sports Sci ; 38(1): 62-69, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31623527

RESUMO

This study investigated whether using an inertial measurement unit (IMU) can identify different walking conditions, including level walking (LW), descent (DC) and ascent (AC) slope walking as well as downstairs (DS) and upstairs (US) walking. Thirty healthy participants performed walking under five conditions. The IMU was stabilised on the exterior of the left shoe. The data from IMU were used to establish a customised prediction model by cut point and a prediction model by using deep learning method. The accuracy of both prediction models was evaluated. The customised prediction model combining the angular velocity of dorsi-plantar flexion in the heel-strike (HS) and toe-off (TO) phases can distinctly determine real conditions during DC and AC slope, DS, and LW (accuracy: 86.7-96.7%) except for US walking (accuracy: 60.0%). The prediction model established by deep learning using the data of three-axis acceleration and three-axis gyroscopes can also distinctly identify DS, US, and LW with 90.2-90.7% accuracy and 84.8% and 82.4% accuracy for DC and AC slope walking, respectively. In conclusion, inertial measurement units can be used to identify walking patterns under different conditions such as slopes and stairs with customised prediction model and deep learning prediction model.


Assuntos
Acelerometria/instrumentação , Aprendizado Profundo , Subida de Escada/fisiologia , Caminhada/fisiologia , Aceleração , Adulto , Fenômenos Biomecânicos , Feminino , Humanos , Masculino , Movimento/fisiologia , Análise e Desempenho de Tarefas , Dispositivos Eletrônicos Vestíveis , Adulto Jovem
7.
J Sports Sci ; 38(1): 46-52, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31658889

RESUMO

The purpose of this study was to determine the influence of pelvis and torso angular jerk on a performance indicator of hitting, specifically hand velocity. Eighteen softball athletes were analysed (20.3 ± 1.6 years; 164.9 ± 24.9 cm; 74.4 ± 14.0 kg). Participants were instructed to execute 3 maximum effort swings off a stationary tee at the middle "strike-zone" location. Angular jerk data were analysed during the acceleration phase of the swing, the time between foot contact and ball contact. Quadratic regression analyses were conducted to examine the relationship of minimal pelvis angular jerk and minimal torso angular jerk to angular hand velocity at ball contact. No significant relationship was found between pelvis angular jerk and angular hand velocity at ball contact (r = 0.192, p = 0.754). The curvilinear regression model for pelvis angular jerk produced: R2 = 0.037; F (2, 17) = 0.288; p = 0.754. Lack of significant findings suggests a relationship between jerk and angular hand velocity does not exist within female softball hitting. Future research should investigate the timing of minimal jerk through the acceleration phase as a predictor of angular hand velocity, rather than the value of jerk itself.


Assuntos
Desempenho Atlético/fisiologia , Beisebol/fisiologia , Mãos/fisiologia , Pelve/fisiologia , Tronco/fisiologia , Aceleração , Fenômenos Biomecânicos , Feminino , Humanos , Destreza Motora/fisiologia , Movimento/fisiologia , Estudos de Tempo e Movimento , Adulto Jovem
8.
Forensic Sci Int ; 306: 110060, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31785511

RESUMO

In order to investigate potential causal relations between the shaking of infants and injuries, biomechanical studies compare brain and skull dynamic behavior during shaking to injury thresholds. However, performing shaking tolerance research on infants, either in vivo or ex vivo, is extremely difficult, if not impossible. Therefore, infant injury thresholds are usually estimated by scaling or extrapolating adult or animal data obtained from crash tests or whiplash experiments. However, it is doubtful whether such data accurately matches the biomechanics of shaking in an infant. Hence some thresholds may be inappropriate to be used for the assessment of inflicted head injury by shaking trauma in infants. A systematic literature review was conducted to 1) provide an overview of existing thresholds for head- and neck injuries related to violent shaking, and 2) to identify and discuss which thresholds have been used or could be used for the assessment of inflicted head injury by shaking trauma in infants. Key findings: The majority of studies establishing or proposing injury thresholds were found to be based on loading cycle durations and loading cycle repetitions that did not resemble those occurring during shaking, or had experimental conditions that were insufficiently documented in order to evaluate the applicability of such thresholds. Injury thresholds that were applied in studies aimed at assessing whether an injury could occur under certain shaking conditions were all based on experiments that did not properly replicate the loading characteristics of shaking. Somewhat validated threshold scaling methods only exist for scaling concussive injury thresholds from adult primate to adult human. Scaling methods that have been used for scaling other injuries, or for scaling adult injury thresholds to infants were not validated. There is a clear and urgent need for new injury thresholds established by accurately replicating the loading characteristics of shaking.


Assuntos
Fenômenos Biomecânicos/fisiologia , Síndrome do Bebê Sacudido/fisiopatologia , Aceleração , Animais , Lesão Axonal Difusa/fisiopatologia , Medicina Legal/métodos , Traumatismos Cranianos Fechados/fisiopatologia , Humanos , Lactente , Hemorragias Intracranianas/fisiopatologia , Modelos Biológicos , Lesões do Pescoço/fisiopatologia , Hemorragia Retiniana/fisiopatologia
9.
J Sports Sci ; 38(3): 248-255, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31726955

RESUMO

Accelerometers are often placed on the tibia to measure segmental accelerations, and external mechanical load during running. However, in applied sport settings it is sometimes preferable to place accelerometers on the dorsal foot to avoid tibial impact injuries. This study aimed to quantify the differences in accelerations measured at the dorsal foot compared with the distal tibia during running. Sixteen recreationally active participants performed a sprint protocol on a non-motorised treadmill. Accelerometers were positioned bilaterally on the medial tibia (TIBLeft and TIBRight), and bilateral dorsal foot surfaces (DORLeft and DORRight). Continuous acceleration signal waveform analysis was performed using one-dimensional statistical parametric mapping (1DSPM). Resultant accelerations were greater for DORLeft than TIBLeft for 60% of the gait cycle (p < 0.001) and greater for DORRight than TIBRight for 50% of the gait cycle (p < 0.003). The larger accelerations at the dorsal foot than the tibia can be explained by movement at the ankle joint, and the placement location relative to the hip. The dorsal foot location can be used to effectively measure accelerations and external mechanical load when it is not feasible to place the accelerometer on the tibia, however results between the two locations should not be compared.


Assuntos
Acelerometria/instrumentação , Monitores de Aptidão Física , Pé/fisiologia , Corrida/fisiologia , Tíbia/fisiologia , Aceleração , Adulto , Articulação do Tornozelo/fisiologia , Fenômenos Biomecânicos , Estudos de Viabilidade , Feminino , Quadril/fisiologia , Humanos , Masculino , Movimento/fisiologia , Percepção/fisiologia , Esforço Físico/fisiologia , Adulto Jovem
10.
Sports Biomech ; 19(2): 141-156, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29972337

RESUMO

The aim of this study was to investigate spatiotemporal and kinematic changes between the initial acceleration, transition and maximum velocity phases of a sprint. Sagittal plane kinematics from five experienced sprinters performing 50-m maximal sprints were collected using six HD-video cameras. Following manual digitising, spatiotemporal and kinematic variables at touchdown and toe-off were calculated. The start and end of the transition phase were identified using the step-to-step changes in centre of mass height and segment angles. Mean step-to-step changes of spatiotemporal and kinematic variables during each phase were calculated. Firstly, the study showed that if sufficient trials are available, step-to-step changes in shank and trunk angles might provide an appropriate measure to detect sprint phases in applied settings. However, given that changes in centre of mass height represent a more holistic measure, this was used to sub-divide the sprints into separate phases. Secondly, during the initial acceleration phase large step-to-step changes in touchdown kinematics were observed compared to the transition phase. At toe-off, step-to-step kinematic changes were consistent across the initial acceleration and transition phases before plateauing during the maximal velocity phase. These results provide coaches and practitioners with valuable insights into key differences between phases in maximal sprinting.


Assuntos
Aceleração , Corrida/fisiologia , Adulto , Desempenho Atlético/fisiologia , Fenômenos Biomecânicos , Índice de Massa Corporal , Feminino , Humanos , Masculino , Tutoria , Postura/fisiologia , Estudos de Tempo e Movimento , Adulto Jovem
11.
Sports Biomech ; 19(2): 168-179, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29877754

RESUMO

The aim of this study was to investigate whether changes on foot-stretcher height were associated with characteristics of better rowing performance. Ten male rowers performed a 200 m rowing trial at their racing rate at each of three foot-stretcher heights. A single scull was equipped with an accelerometer to collect boat acceleration, an impeller with embedded magnets to collect boat speed, specially designed gate sensors to collect gate force and angle, and a compact string potentiometer to collect leg drive length. All sensor signals were sampled at 50 Hz. A one-way repeated measures ANOVA showed that raising foot-stretcher position had a significant reduction on total gate angle and leg drive length. However, a raised foot-stretcher position had a deeper negative peak of boat acceleration at the catch, a lower boat fluctuation, a faster leg drive speed, a larger gate force for the port and starboard side separately. This could be attributed to the optimisation of the magnitude and direction of the foot force with a raised foot-stretcher position. Although there was a significant negative influence of a raised foot-stretcher position on two kinematic variables, biomechanical evidence suggested that a raised foot-stretcher position could contribute to the improvement of rowing performance.


Assuntos
Desempenho Atlético/fisiologia , Pé/fisiologia , Navios/instrumentação , Equipamentos Esportivos , Esportes Aquáticos/fisiologia , Aceleração , Adulto , Fenômenos Biomecânicos , Humanos , Perna (Membro)/fisiologia , Masculino , Adulto Jovem
12.
Sports Biomech ; 19(2): 201-211, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29792560

RESUMO

The purpose of this study was to describe the mechanical characteristics of a trampoline circus act and its individual tracks performed in training and shows using a tri-axial accelerometer. A track is an artist's specific role within a choreographed act. Seven male acrobats performed their trampoline act during training and shows while wearing a triaxial accelerometer and reported ratings of perceived exertion (RPE) after each trial. Average acceleration (AVG), root mean square (RMS), root mean to the fourth (RM4), time spent in specific acceleration ranges and RPE were measured/recorded from training and show acts. Paired t-tests compared dependent variables between training and show. Acceleration AVG, RMS and RM4 were significantly higher (p < 0.05) in training than show. RPE was significantly higher (p < 0.05) in show than training. No significant differences existed in time spent in any of the acceleration ranges between training and show. GPS devices have been used to manage workloads in field sports but are inoperable in theatres. But, inertial measurements may be an effective alternative to describe mechanical demands in theatre or arena environments. Wearable technology may be useful to coaches to improve understanding of track demands to manage artist workloads.


Assuntos
Acelerometria/instrumentação , Desempenho Atlético/fisiologia , Ginástica/fisiologia , Condicionamento Físico Humano/fisiologia , Dispositivos Eletrônicos Vestíveis , Aceleração , Adulto , Fenômenos Biomecânicos , Humanos , Masculino , Percepção/fisiologia , Esforço Físico/fisiologia
13.
Sports Biomech ; 19(2): 189-200, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29768121

RESUMO

Cerebral palsy is known to generally limit range of motion and force producing capability during movement. It also limits sprint performance, but the exact mechanisms underpinning this are not well known. One elite male T36 multiple-Paralympic sprint medallist (T36) and 16 well-trained able-bodied (AB) sprinters each performed 5-6 maximal sprints from starting blocks. Whole-body kinematics (250 Hz) in the block phase and first two steps, and synchronised external forces (1,000 Hz) in the first stance phase after block exit were combined to quantify lower limb joint kinetics. Sprint performance (normalised average horizontal external power in the first stance after block exit) was lower in T36 compared to AB. T36 had lower extensor range of motion and peak extensor angular velocity at all lower limb joints in the first stance after block exit. Positive work produced at the knee and hip joints in the first stance was lower in T36 than AB, and the ratio of positive:negative ankle work produced was lower in T36 than AB. These novel results directly demonstrate the manner in which cerebral palsy limits performance in a competition-specific sprint acceleration movement, thereby improving understanding of the factors that may limit performance in elite sprinters with cerebral palsy.


Assuntos
Aceleração , Desempenho Atlético/fisiologia , Paralisia Cerebral/fisiopatologia , Extremidade Inferior/fisiologia , Corrida/fisiologia , Esportes para Pessoas com Deficiência/fisiologia , Adulto , Articulação do Tornozelo/fisiologia , Fenômenos Biomecânicos , Articulação do Quadril/fisiologia , Humanos , Articulação do Joelho/fisiologia , Masculino , Amplitude de Movimento Articular , Adulto Jovem
14.
Accid Anal Prev ; 134: 105297, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31683233

RESUMO

The motorcyclist is exposed to the risk of falling and impacting ground head-first at a wide range of travelling speeds - from a speed limit of less than 50 km/h on the urban road to the race circuit where speed can reach well above 200 km/h. However, motorcycle helmets today are tested at a single and much lower impact speed, i.e. 30 km/h. There is a knowledge gap in understanding the dynamics and head impact responses at high travelling speeds due to the limitation of existing laboratory rigs. This study used a finite element head model coupled with a motorcycle helmet model to simulate head-first falls at travelling speed (or tangential velocity at impact) from 0 to 216 km/h. The effect of different falling heights (1.6 m and 0.25 m) and coefficient of frictions (0.20 and 0.45) between the helmet outer shell and ground were also examined. The simulation results were analysed together with the analytical model to better comprehend rolling and/or sliding phenomena that are often observed in helmet oblique impacts. Three types of helmet-to-ground interactions are found when the helmet impacts ground from low to high tangential velocities: (1) helmet rolling without slipping; (2) a combination of sliding and rolling; and (3) continuous sliding. The tangential impulse transmitted to the head-helmet system, peak angular head kinematics and brain strain increase almost linearly with the tangential velocity when the helmet rolls but plateaus when the helmet slides. The critical tangential velocity at which the motion transit from the rolling regime to the sliding regime depends on both the falling height and friction coefficient. Typically, for a fall height of 1.63 m and a friction coefficient of 0.45, the rolling/sliding transition occurs at a tangential velocity of 10.8 m/s (38.9 km/h). Low sliding resistance in helmet design, i.e. by the means of a lower friction coefficient between the helmet outer shell and ground, has shown a higher reduction of brain tissue strain in the sliding regime than in the rolling regime. This study uncovers the underlying dynamics of rolling and sliding phenomena in high-speed oblique impacts, which largely affect head impact biomechanics. Besides, the study highlights the importance of testing helmets at speeds covering both the rolling and sliding regime since potential designs for improved head protection at high-speed impacts can be more distinguishable in the sliding regime than in the rolling regime.


Assuntos
Fricção , Dispositivos de Proteção da Cabeça , Motocicletas/estatística & dados numéricos , Aceleração , Acidentes de Trânsito/classificação , Fenômenos Biomecânicos/fisiologia , Traumatismos Craniocerebrais/etiologia , Traumatismos Craniocerebrais/prevenção & controle , Humanos , Fatores de Risco
15.
Gait Posture ; 75: 155-162, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31698186

RESUMO

Individuals with autism spectrum disorder (ASD) can exhibit a range of movement issues, which are often characterized by a general slowing of movement responses that can extend to walking speed. The current study was designed to examine the spatio-temporal features and pattern of acceleration for the trunk, neck and head during walking for a cohort of adults with ASD compared to neurotypical individuals. Twenty young adults with ASD and 20 age-matched neurotypical adults participated in this study. Participants performed five walking trials across a 20ft Protokinetics pressure sensitive surface at their preferred walking speed. Accelerations were collected using three triaxial accelerometers affixed to the head, neck, and lower trunk. Comparisons of acceleration amplitude (i.e., RMS), frequency, segmental gain and regularity (i.e., SampEn) during the walking tasks were performed. Results revealed that the adults with ASD walked slower than the neurotypical persons with a greater proportion of time spent in double stance. Despite walking at a slower pace overall, the adults with ASD exhibited a decreased ability to attenuate gait-related oscillations from the trunk to the head. Overall, these findings suggest that adults with ASD exhibited a decreased ability to accommodate and dampen those accelerations related to walking. As declines in gait speed are often linked with loss of head control, one suggestion is that the inability to appropriately compensate for gait-related oscillations may, in part, explain why persons with ASD walk slower.


Assuntos
Aceleração , Transtorno do Espectro Autista/fisiopatologia , Marcha/fisiologia , Adulto , Estudos de Casos e Controles , Feminino , Cabeça/fisiologia , Humanos , Masculino , Pescoço/fisiologia , Equilíbrio Postural/fisiologia , Análise Espaço-Temporal , Tronco/fisiologia , Velocidade de Caminhada/fisiologia , Adulto Jovem
16.
J Sports Sci Med ; 18(4): 729-737, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31827358

RESUMO

The importance of well trained and stable neck flexors and extensors as well as trunk muscles for intentional headers in soccer is increasingly discussed. The neck flexors and extensors should ensure a coupling of trunk and head at the time of ball contact to increase the physical mass hitting the ball and reduce head acceleration. The aim of the study was to analyze the influence of a 6-week strength training program (neck flexors, neck extensors) on the acceleration of the head during standing, jumping and running headers as well as after fatigue of the trunk muscles on a pendulum header. A total of 33 active male soccer players (20.3 ± 3.6 years, 1.81 ± 0.07 m, 75.5 ± 8.3 kg) participated and formed two training intervention groups (IG1: independent adult team, IG2: independent youth team) and one control group (CG: players from different teams). The training intervention consisted of three exercises for the neck flexors and extensors. The training effects were verified by means of the isometric maximum voluntary contraction (IMVC) measured by a telemetric Noraxon DTS force sensor. The head acceleration during ball contact was determined using a telemetric Noraxon DTS 3D accelerometer. There was no significant change of the IMVC over time between the groups (F=2.265, p=.121). Head acceleration was not reduced significantly for standing (IG1 0.4 ± 2.0, IG2 0.1 ± 1.4, CG -0.4 ± 1.2; F = 0.796, p = 0.460), jumping (IG1-0.7 ± 1.4, IG2-0.2 ± 0.9, CG 0.1 ± 1.2; F = 1.272, p = 0.295) and running (IG1-1.0 ± 1.9, IG2-0.2 ± 1.4, CG -0.1 ± 1.6; F = 1.050, p = 0.362) headers as well as after fatigue of the trunk musculature for post-jumping (IG1-0.2 ± 2.1, IG2-0.6 ± 1.4; CG -0.6 ± 1.3; F = 0.184, p = 0.833) and post-running (IG1-0.3 ± 1.6, IG2-0.7 ± 1.2, CG 0.0 ± 1.4; F = 0.695, p = 0.507) headers over time between IG1, IG2 and CG. A 6-week strength training of the neck flexors and neck extensors could not show the presumed preventive benefit. Both the effects of a training intervention and the consequences of an effective intervention for the acceleration of the head while heading seem to be more complex than previously assumed and presumably only come into effect in case of strong impacts.


Assuntos
Cabeça/fisiologia , Força Muscular/fisiologia , Músculos do Pescoço/fisiologia , Treinamento de Resistência/métodos , Futebol/fisiologia , Aceleração , Acelerometria , Adolescente , Fenômenos Biomecânicos , Concussão Encefálica/prevenção & controle , Humanos , Contração Isométrica/fisiologia , Masculino , Fadiga Muscular/fisiologia , Futebol/lesões , Fatores de Tempo , Adulto Jovem
17.
Biomed Environ Sci ; 32(9): 687-698, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31635684

RESUMO

OBJECTIVE: To observe the effect of high positive acceleration (+Gz) environment on dental implant osseointegration in a rabbit model and to investigate its mechanism. METHODS: Forty-eight New Zealand white rabbits were randomly divided into 6 groups. The rabbit's mandibular incisors were extracted and 1 implant was placed in each socket immediately. After 1 week of rest, the rabbits were exposed to a high +Gz environment, 3 times a week. The rabbits were sacrificed at 3 weeks (2 weeks +Gz exposure), 5 weeks (4 weeks +Gz exposure), and 12 weeks (4 weeks +Gz exposure and 7 weeks normal environment) after surgery, respectively. Specimens were harvested for micro-CT scanning, histological analysis, and real-time polymerase chain reaction examination. RESULTS: Compared with those in the control group, the mRNA expression levels of bone morphogenetic protein-2 (BMP-2), osteopontin (OPN), and transforming growth factor-ß1 (TGF-ß1) were significantly lower (P < 0.05), while the mRNA expression level of receptor activator of nuclear factor κB ligand (RANKL) and the RANKL/osteoprotegerin (OPG) ratio were significantly higher (P < 0.05) at 3 weeks; values of bone volume fraction, trabecular number, bone-implant contact (BIC), and TGF-ß1 and OPG mRNA expression levels were significantly lower (P < 0.05), and the value of trabecular separation, RANKL mRNA expression level and RANKL/OPG ratio were significantly higher (P < 0.05) at 5 weeks; and the value of BIC was still significantly lower (P < 0.05) at 12 weeks in the experimental group. CONCLUSION: Early exposure to the high +Gz environment after implant surgery might have an adverse effect on osseointegration, and its mechanism could be related to the inhibition of osteoblast activity and promotion of osteoclast activity.


Assuntos
Aceleração , Implantes Dentários , Incisivo/cirurgia , Osseointegração , Animais , Masculino , Mandíbula/cirurgia , Medicina Militar , Modelos Animais , Osteoprotegerina/genética , Osteoprotegerina/metabolismo , Ligante RANK/genética , Ligante RANK/metabolismo , Coelhos , Microtomografia por Raio-X
18.
Artigo em Inglês | MEDLINE | ID: mdl-31581592

RESUMO

A neighboring lane's vehicles are potentially important influence factors of traffic safety. In fog weather, drivers will automatically imitate the behaviors demonstrated by other vehicles in the neighboring lane. To illustrate the effect of the imitation phenomenon on traffic safety, this paper develops an extended two-lane car-following model in fog weather. Numerical simulations are carried out to study the effect of imitation on multiple-vehicle collision induced by a sudden stop, as well as perturbation propagation when a small perturbation is added to the uniform traffic flow. The results indicate that the number of collisions depends on the influence coefficient of neighboring lane's vehicles, sensitivity, headway and initial velocity. Furthermore, the number of crumpled vehicles decreases when the imitation phenomenon is taken into account. In addition, lower vehicular velocity in the neighboring lane can reduce the magnitude of acceleration and fluctuation of headway. The perturbation can be absorbed under certain given conditions regarding the imitation phenomenon. Therefore, traffic safety can be improved by considering the effect of the imitation phenomenon on two-lane traffic flow in fog weather. The findings in this study can provide a theoretical reference for the development of multi-lane intermittent release measures in fog weather.


Assuntos
Acidentes de Trânsito/estatística & dados numéricos , Condução de Veículo , Tempo (Meteorologia) , Aceleração , Humanos , Modelos Teóricos , Segurança
19.
Artigo em Inglês | MEDLINE | ID: mdl-31640271

RESUMO

Running performance (RP) and game performance indicators (GPI) are important determinants of success in soccer (football), but there is an evident lack of knowledge about the possible associations between RP and GPI. This study aimed to identify associations between RP and GPI in professional soccer players and to compare RP and GPI among soccer playing positions. One hundred one match performances were observed over the course of half of a season at the highest level of national competition in Croatia. Players (mean ± SD, age: 23.85 ± 2.88 years; body height: 183.05 ± 8.88 cm; body mass: 78.69 ± 7.17 kg) were classified into five playing positions (central defenders (n = 26), full-backs (n = 24), central midfielders (n = 33), wide midfielders (n = 10), and forwards (n = 8). RP, as measured by global positioning system, included the total distance covered, distance covered in five speed categories (walking, jogging, running, high-speed running, and maximal sprinting), total number of accelerations, number of high-intensity accelerations, total number of decelerations, and number of high-intensity decelerations. The GPI were collected by the position-specific performance statistics index (InStat index). The average total distance was 10,298.4 ± 928.7 m, with central defenders having the shortest and central midfielders having the greatest covered distances. The running (r = 0.419, p = 0.03) and high-intensity accelerations (r = 0.493, p = 0.01) were correlated with the InStat index for central defenders. The number of decelerations of full-backs (r = -0.43, p = 0.04) and the distance covered during sprinting of forwards (r = 0.80, p = 0.02) were associated with their GPI obtained by InStat index. The specific correlations between RP and GPI should be considered during the conditioning process in soccer. The soccer training should follow the specific requirements of the playing positions established herein, which will allow players to meet the game demands and to perform successfully.


Assuntos
Desempenho Atlético , Corrida , Futebol , Aceleração , Adulto , Atletas , Croácia , Humanos , Masculino , Caminhada , Adulto Jovem
20.
Molecules ; 24(20)2019 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-31614514

RESUMO

We apply the formally exact quantum power functional framework (J. Chem. Phys. 2015, 143, 174108) to a one-dimensional Hooke's helium model atom. The physical dynamics are described on the one-body level beyond the density-based adiabatic approximation. We show that gradients of both the microscopic velocity and acceleration field are required to correctly describe the effects due to interparticle interactions. We validate the proposed analytical forms of the superadiabatic force and transport contributions by comparison to one-body data from exact numerical solution of the Schrödinger equation. Superadiabatic contributions beyond the adiabatic approximation are important in the dynamics and they include effective dissipation.


Assuntos
Hélio/química , Teoria Quântica , Soluções/química , Aceleração , Simulação por Computador
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