Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 25
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Sci Rep ; 10(1): 1150, 2020 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-31980675

RESUMO

Insects of the family Orthoptera: Acrididae including grasshoppers and locust devastate crops and eco-systems around the globe. The effective control of these insects requires large numbers of trained extension agents who try to spot concentrations of the insects on the ground so that they can be destroyed before they take flight. This is a challenging and difficult task. No automatic detection system is yet available to increase scouting productivity, data scale and fidelity. Here we demonstrate MAESTRO, a novel grasshopper detection framework that deploys deep learning within RBG images to detect insects. MAESTRO uses a state-of-the-art two-stage training deep learning approach. The framework can be deployed not only on desktop computers but also on edge devices without internet connection such as smartphones. MAESTRO can gather data using cloud storge for further research and in-depth analysis. In addition, we provide a challenging new open dataset (GHCID) of highly variable grasshopper populations imaged in Inner Mongolia. The detection performance of the stationary method and the mobile App are 78 and 49 percent respectively; the stationary method requires around 1000 ms to analyze a single image, whereas the mobile app uses only around 400 ms per image. The algorithms are purely data-driven and can be used for other detection tasks in agriculture (e.g. plant disease detection) and beyond. This system can play a crucial role in the collection and analysis of data to enable more effective control of this critical global pest.

2.
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
3.
Sports Med ; 49(12): 1975, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31583534

RESUMO

No sources of funding were used in the preparation of this article.

4.
Sports Med ; 49(12): 1957-1973, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31493205

RESUMO

BACKGROUND: The swim start requires an explosive muscular response of the lower body musculature to effectively initiate movement off the starting blocks. There are currently key gaps in the literature evaluating the relationship between dry-land resistance training and swim start performance and the effects of this training on swim start performance, as assessed by the time to 5, 10 or 15 m. OBJECTIVES: The aims of this systematic review were to critically appraise the current literature on (1) the acute relationship between dry-land resistance training and swim start performance and (2) the acute and chronic effects of dry-land resistance training on swim start performance. METHODS: An electronic search using AusportMed, Embase, Medline (Ovid), SPORTDiscus and Web of Science was performed. The methodological quality of the studies was evaluated using the Newcastle-Ottawa quality assessment scale (NOS) (cross-sectional studies) and the Physiotherapy Evidence Database (PEDro) scale (intervention studies). RESULTS: Sixteen studies met the eligibility criteria, although the majority did not utilise the starting blocks or technique currently used in elite swimming. Swim start performance was near perfectly related (r > 0.90) to vertical bodyweight jumps and jump height. Post-activation potentiation and plyometrics were found to produce significant improvements in acute and chronic swim start performance, respectively. CONCLUSION: While there appears to be strong evidence supporting the use of plyometric exercises such as vertical jumps for monitoring and improving swim start performance, future studies need to replicate these findings using current starting blocks and techniques and compare the chronic effects of a variety of resistance training programmes.

5.
Sports Biomech ; 18(1): 88-99, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29125040

RESUMO

Radar technology can be used to perform horizontal force-velocity-power profiling during sprint-running. The aim of this study was to determine the reliability of radar-derived profiling results from short sprint accelerations. Twenty-seven participants completed three 30 m sprints (intra-day analysis), and nine participants completed the testing session on four separate days (inter-day analysis). The majority of radar-derived kinematic and kinetic descriptors of short sprint performance had acceptable intra-day and inter-day reliability [intraclass correlation coefficient (ICC) ≥ 0.75 and coefficient of variation (CV) ≤ 10%], but split times over the initial 10 m and some variables that include a horizontal force component had only moderate relative reliability (ICC = 0.49-0.74). Comparing the average of two sprint trials between days resulted in acceptable reliability for all variables except the relative slope of the force-velocity relationship (S Fvrel; ICC = 0.74). Practitioners should average sprint test results over at least two trials to reduce measurement variability, particularly for outcome variables with a horizontal force component and for sprint distances of less than 10 m from the start.


Assuntos
Aceleração , Radar , Corrida/fisiologia , Adolescente , Fenômenos Biomecânicos , Humanos , Masculino , Fenômenos Mecânicos , Reprodutibilidade dos Testes
6.
J Strength Cond Res ; 32(10): 2750-2761, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30113915

RESUMO

Douglas, J, Pearson, S, Ross, A, and McGuigan, M. Effects of accentuated eccentric loading on muscle properties, strength, power, and speed in resistance-trained rugby players. J Strength Cond Res 32(10): 2750-2761, 2018-The purpose of this study was to determine the effects of slow and fast tempo resistance training incorporating accentuated eccentric loading (AEL) compared with traditional resistance training (TRT) in trained rugby players. Fourteen subjects (19.4 ± 0.8 years, 1.82 ± 0.05 m, 97.0 ± 11.6 kg, and relative back squat 1 repetition maximum [1RM]: 1.71 ± 0.24 kg·BM) completed either AEL (n = 7) or TRT (n = 7) strength and power protocols. Two 4-week phases of training were completed. The first phase emphasized a slow eccentric tempo, and the second phase emphasized a fast eccentric tempo. Back squat 1RM, inertial load peak power, drop jump reactive strength index (RSI), 40-m speed, maximum sprinting velocity (Vmax), and vastus lateralis (VL) muscle architectural variables were determined at baseline and after each phase of training. Slow AEL elicited superior improvements in back squat 1RM (+0.12 kg·BM; effect size [ES]: 0.48; and 90% confidence interval [CI]: 0.14, 0.82), 40-m time (-0.07 seconds; ES: 0.28; and CI: 0.01-0.55), and Vmax (+0.20 m·s; ES: 0.52; and CI: 0.18-0.86) vs. slow TRT. Fast AEL elicited a small increase in RSI but impaired speed. There was a likely greater increase in peak power with fast TRT (+0.72 W·kg; ES: 0.40; and CI: 0.00-0.79) vs. fast AEL alongside a small increase in VL pennation angle. The short-term incorporation of slow AEL was superior to TRT in improving strength and maximum velocity sprinting speed in rugby players undertaking a concurrent preparatory program. The second 4-week phase of fast AEL may have exceeded recovery capabilities compared with fast TRT.


Assuntos
Futebol Americano/fisiologia , Força Muscular , Músculo Esquelético/fisiologia , Treinamento de Resistência/métodos , Teste de Esforço , Humanos , Masculino , Adulto Jovem
7.
Sensors (Basel) ; 18(8)2018 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-30110960

RESUMO

Machine learning has emerged with big data technologies and high-performance computing to create new opportunities for data intensive science in the multi-disciplinary agri-technologies domain. In this paper, we present a comprehensive review of research dedicated to applications of machine learning in agricultural production systems. The works analyzed were categorized in (a) crop management, including applications on yield prediction, disease detection, weed detection crop quality, and species recognition; (b) livestock management, including applications on animal welfare and livestock production; (c) water management; and (d) soil management. The filtering and classification of the presented articles demonstrate how agriculture will benefit from machine learning technologies. By applying machine learning to sensor data, farm management systems are evolving into real time artificial intelligence enabled programs that provide rich recommendations and insights for farmer decision support and action.

9.
Int J Sports Physiol Perform ; 13(2): 246-249, 2018 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-28488905

RESUMO

PURPOSE: To assess the longitudinal evolution of tactical behaviors used to medal in men's 800-m Olympic Games (OG) or world-championship (WC) events in the recent competition era (2000-2016). METHODS: Thirteen OG and WC events were characterized for 1st- and 2nd-lap splits using available footage from YouTube. Positive pacing strategies were defined as a faster 1st lap. Season's best 800-m time and world ranking, reflective of an athlete's "peak condition," were obtained to determine relationships between adopted tactics and physical condition prior to the championships. Seven championship events provided coverage of all medalists to enable determination of average 100-m speed and sector pacing of medalists. RESULTS: From 2011 onward, 800-m OG and WC medalists showed a faster 1st lap by 2.2 ± 1.1 s (mean, ±90% confidence limits; large difference, very likely), contrasting a possibly faster 2nd lap from 2000 to 2009 (0.5, ±0.4 s; moderate difference). A positive pacing strategy was related to a higher world ranking prior to the championships (r = .94, .84-.98; extremely large, most likely). After 2011, the fastest 100-m sector from 800-m OG and WC medalists was faster than before 2009 by 0.5, ±0.2 m/s (large difference, most likely). CONCLUSIONS: A secular change in tactical racing behavior appears evident in 800-m championships; since 2011, medalists have largely run faster 1st laps and have faster 100-m sector-speed requirements. This finding may be pertinent for training, tactical preparation, and talent identification of athletes preparing for 800-m running at OGs and WCs.


Assuntos
Desempenho Atlético/fisiologia , Comportamento Competitivo/fisiologia , Corrida/fisiologia , Desempenho Atlético/psicologia , Tomada de Decisões/fisiologia , Humanos , Masculino , Condicionamento Físico Humano , Corrida/psicologia
10.
J Strength Cond Res ; 32(6): 1562-1570, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-28930875

RESUMO

Douglas, J, Pearson, S, Ross, A, and McGuigan, M. Kinetic determinants of reactive strength in highly trained sprint athletes. J Strength Cond Res 32(6): 1562-1570, 2018-The purpose of this study was to determine the braking and propulsive phase kinetic variables underpinning reactive strength in highly trained sprint athletes in comparison with a nonsprint-trained control group. Twelve highly trained sprint athletes and 12 nonsprint-trained participants performed drop jumps (DJs) from 0.25, 0.50, and 0.75 m onto a force plate. One familiarization session was followed by an experimental testing session within the same week. Reactive strength index (RSI), contact time, flight time, and leg stiffness were determined. Kinetic variables including force, power, and impulse were assessed within the braking and propulsive phases. Sprint-trained athletes demonstrated higher RSI vs. nonsprint-trained participants across all drop heights {3.02 vs. 2.02; ES (±90% confidence limit [CL]): 3.11 ± 0.86}. This difference was primarily attained by briefer contact times (0.16 vs. 0.22 seconds; effect size [ES]: -1.49 ± 0.53) with smaller differences observed for flight time (0.50 vs. 0.46 seconds; ES: 0.53 ± 0.58). Leg stiffness, braking and propulsive phase force, and power were higher in sprint-trained athletes. Very large differences were observed in mean braking force (51 vs. 38 N·kg; ES: 2.57 ± 0.73) which was closely associated with contact time (r ±90% CL: -0.93 ± 0.05). Sprint-trained athletes exhibited superior reactive strength than nonsprint-trained participants. This was due to the ability to strike the ground with a stiffer leg spring, an enhanced expression of braking force, and possibly an increased utilization of elastic structures. The DJ kinetic analysis provides additional insight into the determinants of reactive strength which may inform subsequent testing and training.


Assuntos
Força Muscular , Músculo Esquelético/fisiologia , Condicionamento Físico Humano/fisiologia , Corrida/fisiologia , Adolescente , Adulto , Teste de Esforço , Humanos , Cinética , Masculino , Adulto Jovem
11.
Int J Sports Physiol Perform ; 12(10): 1329-1334, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-28290718

RESUMO

PURPOSE: To examine relationships between methods of lower-limb stiffness and their associations with running economy (RE) and maximal velocity (vmax) in middle-distance (MD) runners. METHODS: Eleven highly trained male MD runners performed a series of mechanical and physiological tests to determine maximal overground sprint speed, RE, and [Formula: see text]. Achilles tendon stiffness (kT) was estimated using ultrasonography during maximal isometric ankle plantar flexion. Global stiffness qualities were evaluated using a spring-mass model, providing measures of leg (kleg) and vertical stiffness (kvert) during running and jumping, respectively. RESULTS: Very large (r = -.70) and large (r = -.60) negative relationships existed between RE and kT and kvert, during plantar flexion and unilateral jumps, respectively. There were large (r = .63) and extremely large (r = -.92) associations between kvert and kT and kleg during sprinting, respectively. Runners' vmax had large positive associations between kT (r = .52) and kleg (r = .59) during sprinting. CONCLUSIONS: In well-trained MD athletes, greater stiffness appears linked to faster and more economical running. Although kT had the strongest relationship with RE, kleg while sprinting and kvert in maximal unilateral jumps may be more practical measures of stiffness. Agreement between global stiffness assessments and kT highlights the energy contribution of the Achilles tendon to running efficiency and velocity. Further research incorporating these assessment tools could help establish more comprehensive mechanical and metabolic athlete profiles and further our understanding of training adaptations, especially stiffness modification, longitudinally.


Assuntos
Tendão do Calcâneo/fisiologia , Desempenho Atlético/fisiologia , Corrida/fisiologia , Adolescente , Atletas , Fenômenos Biomecânicos , Estudos Transversais , Humanos , Perna (Membro)/fisiologia , Masculino , Esforço Físico , Adulto Jovem
12.
Sports Med ; 47(4): 663-675, 2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-27638040

RESUMO

An eccentric contraction involves the active lengthening of muscle under an external load. The molecular and neural mechanisms underpinning eccentric contractions differ from those of concentric and isometric contractions and remain less understood. A number of molecular theories have been put forth to explain the unexplained observations during eccentric contractions that deviate from the predictions of the established theories of muscle contraction. Postulated mechanisms include a strain-induced modulation of actin-myosin interactions at the level of the cross-bridge, the activation of the structural protein titin, and the winding of titin on actin. Accordingly, neural strategies controlling eccentric contractions also differ with a greater, and possibly distinct, cortical activation observed despite an apparently lower activation at the level of the motor unit. The characteristics of eccentric contractions are associated with several acute physiological responses to eccentrically-emphasised exercise. Differences in neuromuscular, metabolic, hormonal and anabolic signalling responses during, and following, an eccentric exercise bout have frequently been observed in comparison to concentric exercise. Subsequently, the high levels of muscular strain with such exercise can induce muscle damage which is rarely observed with other contraction types. The net result of these eccentric contraction characteristics and responses appears to be a novel adaptive signal within the neuromuscular system.


Assuntos
Exercício/fisiologia , Contração Isométrica/fisiologia , Contração Muscular/fisiologia , Humanos , Músculo Esquelético
13.
Sports Med ; 47(5): 917-941, 2017 May.
Artigo em Inglês | MEDLINE | ID: mdl-27647157

RESUMO

BACKGROUND: Resistance training is an integral component of physical preparation for athletes. A growing body of evidence indicates that eccentric strength training methods induce novel stimuli for neuromuscular adaptations. OBJECTIVE: The purpose of this systematic review was to determine the effects of eccentric training in comparison to concentric-only or traditional (i.e. constrained by concentric strength) resistance training. METHODS: Searches were performed using the electronic databases MEDLINE via EBSCO, PubMed and SPORTDiscus via EBSCO. Full journal articles investigating the long-term (≥4 weeks) effects of eccentric training in healthy (absence of injury or illness during the 4 weeks preceding the training intervention), adult (17-35 years), human participants were selected for the systematic review. A total of 40 studies conformed to these criteria. RESULTS: Eccentric training elicits greater improvements in muscle strength, although in a largely mode-specific manner. Superior enhancements in power and stretch-shortening cycle (SSC) function have also been reported. Eccentric training is at least as effective as other modalities in increasing muscle cross-sectional area (CSA), while the pattern of hypertrophy appears nuanced and increased CSA may occur longitudinally within muscle (i.e. the addition of sarcomeres in series). There appears to be a preferential increase in the size of type II muscle fibres and the potential to exert a unique effect upon fibre type transitions. Qualitative and quantitative changes in tendon tissue that may be related to the magnitude of strain imposed have also been reported with eccentric training. CONCLUSIONS: Eccentric training is a potent stimulus for enhancements in muscle mechanical function, and muscle-tendon unit (MTU) morphological and architectural adaptations. The inclusion of eccentric loads not constrained by concentric strength appears to be superior to traditional resistance training in improving variables associated with strength, power and speed performance.


Assuntos
Adaptação Fisiológica , Exercício/fisiologia , Contração Muscular/fisiologia , Fibras Musculares Esqueléticas/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Adolescente , Adulto , Humanos , Educação Física e Treinamento , Treinamento de Resistência/métodos
14.
Sports (Basel) ; 4(3)2016 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-29910285

RESUMO

Grinding is a key physical element in America's Cup sailing. This study aimed to describe kinematics and muscle activation patterns in relation to torque applied in forward and backward grinding. Ten male America's Cup sailors (33.6 ± 5.7 years, 97.9 ± 13.4 kg, 186.6 ± 7.4 cm) completed forward and backward grinding on a customised grinding ergometer. In forward grinding peak torque (77 Nm) occurred at 95° (0° = crank vertically up) on the downward section of the rotation at the end of shoulder flexion and elbow extension. Backward grinding torque peaked at 35° (69 Nm) following the pull action (shoulder extension, elbow flexion) across the top of the rotation. During forward grinding, relatively high levels of torque (>50 Nm) were maintained through the majority (72%) of the cycle, compared to 47% for backward grinding, with sections of low torque corresponding with low numbers of active muscles. Variation in torque was negatively associated with forward grinding performance (r = -0.60; 90% CI -0.88 to -0.02), but positively associated with backward performance (r = 0.48; CI = -0.15 to 0.83). Magnitude and distribution of torque generation differed according to grinding direction and presents an argument for divergent training methods to improve forward and backward grinding performance.

15.
Med Sci Sports Exerc ; 46(6): 1227-34, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24576862

RESUMO

PURPOSE: Tracking athletes' performances over time is important but problematic for sports with large environmental effects. Here we have developed career performance trajectories for elite triathletes, investigating changes in swim, cycle, run stages, and total performance times while accounting for environmental and other external factors. METHODS: Performance times of 337 female and 427 male triathletes competing in 419 international races between 2000 and 2012 were obtained from triathlon.org. Athletes were categorized according to any top 16 placing at World Championships or Olympics between 2008 and 2012. A mixed linear model accounting for race distance (sprint and Olympic), level of competition, calendar-year trend, athlete's category, and clustering of times within athletes and races was used to derive athletes' individual quadratic performance trajectories. These trajectories provided estimates of age of peak performance and predictions for the 2012 London Olympic Games. RESULTS: By markedly reducing the scatter of individual race times, the model produced well-fitting trajectories suitable for comparison of triathletes. Trajectories for top 16 triathletes showed different patterns for race stages and differed more among women than among men, but ages of peak total performance were similar for men and women (28 ± 3 yr, mean ± SD). Correlations between observed and predicted placings at Olympics were slightly higher than those provided by placings in races before the Olympics. CONCLUSIONS: Athletes' trajectories will help identify talented athletes and their weakest and strongest stages. The wider range of trajectories among women should be taken into account when setting talent identification criteria. Trajectories offer a small advantage over usual race placings for predicting men's performance. Further refinements, such as accounting for individual responses to race conditions, may improve utility of performance trajectories.


Assuntos
Desempenho Atlético/fisiologia , Modelos Lineares , Adulto , Fatores Etários , Ciclismo/fisiologia , Comportamento Competitivo/fisiologia , Meio Ambiente , Feminino , Humanos , Masculino , Valores de Referência , Corrida/fisiologia , Natação/fisiologia
16.
Sports Biomech ; 8(3): 245-54, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19891202

RESUMO

Understanding how loading affects power production in resistance training is a key step in identifying the most optimal way of training muscular power - an essential trait in most sporting movements. Twelve elite male sailors with extensive strength-training experience participated in a comparison of kinematics and kinetics from the upper body musculature, with upper body push (bench press) and pull (bench pull) movements performed across loads of 10-100% of one repetition maximum (1RM). 1RM strength and force were shown to be greater in the bench press, while velocity and power outputs were greater for the bench pull across the range of loads. While power output was at a similar level for the two movements at a low load (10% 1RM), significantly greater power outputs were observed for the bench pull in comparison to the bench press with increased load. Power output (Pmax) was maximized at higher relative loads for both mean and peak power in the bench pull (78.6 +/- 5.7% and 70.4 +/- 5.4% of 1RM) compared to the bench press (53.3 +/- 1.7% and 49.7 +/- 4.4% of 1RM). Findings can most likely be attributed to differences in muscle architecture, which may have training implications for these muscles.


Assuntos
Exercício/fisiologia , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Aptidão Física/fisiologia , Ombro/fisiologia , Análise e Desempenho de Tarefas , Levantamento de Peso/fisiologia , Adulto , Humanos , Masculino , Amplitude de Movimento Articular/fisiologia
17.
J Strength Cond Res ; 23(8): 2256-65, 2009 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-19826300

RESUMO

This study sought to compare the anthropometric profiles of 17 weaker and 17 stronger Australasian and Pacific powerlifters who had competed in a regional-, national-, or international-level powerlifting competition in New Zealand. Stronger lifters were defined as those having a Wilks score greater than 410, whereas those in the weaker group had a Wilks score less than 370. Each powerlifter was assessed for 37 anthropometric dimensions by International Society for the Advancement of Kinanthropometry (ISAK) level II and III accredited anthropometrists. Because all powerlifters were highly mesomorphic and possessed large girths and bone breadths, both in absolute terms and when expressed as Phantom-Z scores compared through the Phantom, relatively few significant anthropometric differences were observed. However, stronger lifters had significantly greater muscle mass and larger muscular girths in absolute terms as well as greater Brugsch Index (chest girth/height) and "Phantom"-normalized muscle mass, upper arm, chest, and forearm girths. In terms of the segment lengths and bone breadths, the only significant difference was that stronger lifters had a significantly shorter lower leg than weaker lifters. Because the majority of the significant differences were for muscle mass and muscular girths, it would appear likely that these differences contributed to the stronger lifters' superior performance. Powerlifters may therefore need to devote some of their training to the development of greater levels of muscular hypertrophy if they wish to continue to improve their performance. To better understand the anthropometric determinants of muscular strength, future research should recruit larger samples (particularly of elite lifters) and follow these subjects prospectively.


Assuntos
Antropometria , Força Muscular/fisiologia , Levantamento de Peso/fisiologia , Adulto , Análise de Variância , Estudos Transversais , Humanos , Masculino , Valor Preditivo dos Testes
18.
J Strength Cond Res ; 23(6): 1883-9, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19675468

RESUMO

The purpose grinding is a physically demanding component of America's Cup sailing that is important to overall team performance, but little research is available on the determinants of grinding performance. We examined the relationship between various measures of muscular performance and the performance of upper-body grinding. Eleven elite male America's Cup sailors (33.9 +/- 5.5 yr, 97.8 +/- 12.5 kg, 186.0 +/- 7.1 cm) who performed grinding as part of their on-board role with extensive strength training experience participated in this study. Muscular performance testing examined the force, velocity, and power capabilities of the upper-body musculature, with upper-body push (bench press) and pull (bench pull) movements performed across loads of 10-100% of 1 repetition maximum (1RM). Functional grinding performance was examined for both forward and backward grinding and at 2 different resistances (moderate = 48 N x m, heavy = 68 N x m) using a land-based ergometer. Bench press 1RM and maximum force capability were the measures demonstrating the strongest correlation with forward grinding performance (r = 0.88-0.99 and 0.87-0.99, respectively), with the relationship increasing with grinding load. For backward grinding, there was a very strong relationship with bench pull maximum power (r = 0.85-0.98) in addition to 1RM (r = 0.90-0.95) and maximum force (r = 0.87-0.95). It appears that although maximal strength is a crucial muscular performance characteristic for grinding performance in all conditions, for backward grinding, there is the additional need to focus on the development of speed strength/power to maximize performance gains. This information was used by the Emirates Team New Zealand physical conditioner to develop a conditioning intervention to help improve grinding performance.


Assuntos
Força Muscular/fisiologia , Esportes/fisiologia , Adulto , Atletas , Desempenho Atlético/fisiologia , Teste de Esforço , Humanos , Masculino , Resistência Física/fisiologia , Treinamento de Resistência , Navios , Levantamento de Peso/fisiologia
19.
Sports Biomech ; 8(4): 334-44, 2009 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-20169762

RESUMO

This study determined whether backward grinding performance in America's Cup sailing could be improved using a training intervention to increase power capability in the upper-body pull movement. Fourteen elite male sailors (34.9 +/- 5.9 years; 98.1 +/- 14.4 kg; 186.6 +/- 7.7 cm) were allocated into experimental (speed-focussed) and control groups. Grinding performance was assessed using a grinding ergometer and an instrumented Smith machine measured force, velocity and power during the bench pull exercise. Conventional training produced significant improvements in bench pull 1 RM (5.2 +/- 4.0%; p = 0.016) and maximum force production (5.4 +/- 4.0%; p = 0.014). Speed-focussed training improved maximum power (7.8 +/- 4.9%; p = 0.009), power at 1 RM (10.3 +/- 8.9%; p = 0.019) and maximum velocity (8.4 +/- 2.6%; p = 0.0002). Backward grinding performance showed greater improvements in the experimental group than the control group for moderate (+1.8%) and heavy load (+6.0%) grinding. Changes in maximum power output and power at 1 RM had large correlations (r = 0.56-0.61) with changes in both moderate and heavy load grinding performance. Time to peak force had the strongest relationship, explaining 70% of the change in heavy load grinding performance. Although the performance benefit was not entirely clear the likelihood of a detrimental effect was low (< 5%) and therefore implementation could be recommended.


Assuntos
Braço/fisiologia , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Esforço Físico/fisiologia , Desempenho Psicomotor/fisiologia , Treinamento de Resistência/métodos , Navios , Humanos , Masculino , Adulto Jovem
20.
J Sports Sci ; 26(5): 531-41, 2008 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-18274950

RESUMO

We examined sexual dimorphism in the anthropometry of 68 Australasian and Pacific powerlifters (14 females, 54 males) who were competing in one of two national or international powerlifting competitions held in New Zealand. All powerlifters were assessed for 37 anthropometric dimensions by ISAK (International Society for the Advancement of Kinanthropometry) Level II and III accredited anthropometrists. While the powerlifters were highly mesomorphic and possessed large girths and bone breadths, both in absolute terms and when expressed as Z(p)-scores compared through the Phantom (Ross & Wilson, 1974), these characteristics were often more pronounced in male than female lifters. No significant inter-gender differences in any of the measures of adiposity were observed. When normalized through the Phantom, the female and male powerlifters had relatively similar segment lengths and bone breadths, indicating that regardless of gender, competitive powerlifters possess comparable skeletal proportions. These results indicate that although competitive powerlifters exhibit sexual dimorphism for many absolute anthropometric measures, little dimorphism is found for measures of adiposity and for proportional segment lengths and bone breadths. These results further support the importance of anthropometric profiling for powerlifting, and suggest that successful male and female powerlifters will possess similar proportional characteristics.


Assuntos
Caracteres Sexuais , Levantamento de Peso/fisiologia , Adulto , Antropometria , Feminino , Humanos , Masculino
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA