Figure Skating     

Deborah King  Sarah Smith  Brian Higginson  Barry Muncasy  Gary Scheirman 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(1):109-123

The purpose of this study was to compare triple (T) and quadruple (Q) toe‐loop figure skating jumps and quantify basic characteristics of these jumps to provide information to coaches that will assist them in teaching quadruple toe‐loops to elite figure skaters. High‐speed video was taken during men's practice and competition sessions at the 2002 Salt Lake City Winter Olympics; three‐dimensional analyses of selected triple and quadruple jumps were completed. The most significant difference between triple and quadruple toe‐loops was an increase in rotational velocity in the air. Additionally, increased vertical velocity at take‐off and subsequent time in the air were also observed. Three main conclusions were developed: 1) The timing of rotation of the hips and shoulders was different for quadruple toe‐loops compared to triples with the differences being observed before toe‐pick; 2) Increases in rotational velocity occurred primarily as a result of the skaters assuming different body positions from take‐off through landing which resulted in tighter rotating positions for longer durations of the jump; 3) Greater vertical velocity was gained during the propulsive phase due to the extension of the legs during the press off the ice.  相似文献   

The influence of deformation on barbell mechanics during the clean pull     

Loren Z. F. Chiu  Brian K. Schilling  Andrew C. Fry  George J. Salem 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(2):260-273

For simplicity of biomechanical analyses, the weightlifting barbell is typically modelled as a rigid, non-deformable object. Most coaches and weightlifters, however, are aware of the elastic nature of the barbell, and its influence on the successful completion of lifting attempts. Variables such as velocity, work performed, and power output are indicators of the quality of performance during the snatch, clean, and related weightlifting pulling movements. The aim of this study was to establish whether differences exist in determining these biomechanical parameters when the centre of the barbell is analysed compared with each end of the barbell. Nine men performed three maximal-effort repetitions in the clean pull exercise at 85% of their self-reported single repetition maximum (1-RM) clean (90–155 kg) using a barbell instrumented for mechanical analysis. Results indicated that peak barbell speed was 5–30% (P < 0.05) lower for the centre of the barbell than the ends. Although differences (P < 0.05) in kinetic and potential energy were found between the centre and ends of the bar, differences between total work performed were small ( < 6%; P < 0.05) and no differences were observed for average power (P > 0.05). Although approximately the same work and power occur for the centre and ends of the barbell, they manifest as different kinematics as a result of the elastic nature of the equipment. The elastic characteristics should be considered when selecting instrumentation and variables for research involving barbells. Coaches should be aware of the elasticity of barbells, including selecting appropriate viewing angles as well as understanding how deformation may affect the ends of the barbell relative to the centre.  相似文献   

Adductor longus mechanics during the maximal effort soccer kick     

Brian L. Charnock  Cara L. Lewis  William E. Garrett JR. 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):223-234

Groin pain is a common cause of athletic disability and often involves the adductor longus. A common complaint of patients with groin problems is pain while preparing to kick the ball. The purpose of this study was to examine muscle length and activation of the adductor longus while kicking a soccer ball. Three-dimensional joint positions and muscle activation were obtained from 15 National Collegiate Athletic Association (NCAA) Division 1 male soccer players during maximal effort kicks. Musculoskeletal modeling techniques incorporating joint position and muscle attachments were used to estimate adductor longus length from the beginning of the kicking leg's swing phase until ball strike. The maximum rate of stretch of the adductor longus (22.3 ± 5.3 cm/s) and maximum hip extension (23.3 ± 8.8°) occurred near 40% of swing phase. Activation of the adductor longus occurred between 10% and 50% of the swing phase. Adductor longus maximum length occurred at 65% of the swing phase. Maximum hip abduction (25.3 ± 5.4°) occurred at 80% of swing phase. The adductor longus appears to be at risk of strain injury during its transition from hip extension to hip flexion. This knowledge could be applied to muscle injury prevention and rehabilitation programs to aid with treatment of adductor longus related groin pain.  相似文献   

Net forces during tethered simulation of underwater streamlined gliding and kicking techniques of the freestyle turn     

Andrew D. Lyttle  Brian A. Blanksby  Bruce C. Elliott  David G. Lloyd 《Journal of sports sciences》2013,31(10):801-807

Weassessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m· s-1 . At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m· s-1 ) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another.  相似文献   

Movement patterns in cricket vary by both position and game format     

Carl J. Petersen  David Pyne  Brian Dawson  Marc Portus  Aaron Kellett 《Journal of sports sciences》2013,31(1):45-52

Abstract

We compared the movement patterns of cricketers in different playing positions across three formats of cricket (Twenty20, One Day, multi-day matches). Cricket Australia Centre of Excellence cricketers (n = 42) from five positions (batting, fast bowling, spin bowling, wicketkeeping, and fielding) had their movement patterns (walk, jog, run, stride, and sprint) quantified by global positioning system (GPS) technology over two seasons. Marked differences in movement patterns were evident between positions and game formats, with fast bowlers undertaking the greatest workload of any position in cricket. Fast bowlers sprinted twice as often, covered over three times the distance sprinting, with much smaller work-to-recovery ratios than other positions. Fast bowlers during multi-day matches covered 22.6 ± 4.0 km (mean ± s) total distance in a day (1.4 ± 0.9 km in sprinting). In comparison, wicketkeepers rarely sprinted, despite still covering a daily total distance of 16.6 ± 2.1 km. Overall, One Day and Twenty20 cricket required ～50 to 100% more sprinting per hour than multi-day matches. However, multi-day cricket's longer duration resulted in 16–130% more sprinting per day. In summary, the shorter formats (Twenty20 and One Day) are more intensive per unit of time, but multi-day cricket has a greater overall physical load.  相似文献   

Movement patterns and physical strain during a novel,simulated cricket batting innings (BATEX)     

Laurence Houghton  Brian Dawson  Jonas Rubenson  Martin Tobin 《Journal of sports sciences》2013,31(8):801-809

Abstract

A simulated cricket batting innings was developed to replicate the physical demands of scoring a century during One-Day International cricket. The simulated innings requires running-between-the-wickets across six 5-over stages, each of 21 min duration. To validate whether the simulated batting innings is reflective of One-Day International batting, movement patterns were collected using a global positioning system (GPS) and compared with previous research. In addition, indicators of physical strain were recorded (heart rate, jump heights, sweat loss, tympanic temperature). Nine club cricketers (mean ± s: age 20 ± 3 years; body mass 79.5 ± 7.9 kg) performed the simulated innings outdoors. There was a moderate trend for distance covered in the simulated innings to be less than that during One-Day batting (2171 ± 157 vs. 2476 ± 631 m · h^?1; effect size = 0.78). This difference was largely explained by a strong trend for less distance covered walking in the simulated innings than in One-Day batting (1359 ± 157 vs. 1604 ± 438 m · h^?1; effect size = 1.61). However, there was a marked trend for distance covered both striding and sprinting to be greater in the simulated innings than in One-Day batting (effect size > 1.2). Practically, the simulated batting innings may be used for match-realistic physical training and as a research protocol to assess the demands of prolonged, high-intensity cricket batting.  相似文献   

Effect of precooling and acclimation on repeat-sprint performance in heat     

Carly Brade  Brian Dawson  Karen Wallman 《Journal of sports sciences》2013,31(7):779-786

Abstract

This study determined whether precooling would have an additive effect on repeat-sprint cycling performance in heat following partial acclimation. Ten males completed three trials; Pre Acclimation (Pre Acc) and two Post Acclimation trials, one with precooling (ice jacket and slushy; Post Acc +PC) and another without (Post Acc). Trials consisted of a 30-min baseline period followed by a 70-min repeat-sprint protocol in ～35°C and 60% relative humidity. Separating pre and post trials were five heat acclimation sessions. Although no significant differences were found for performance variables, inferential statistical analysis resulted in moderate effect sizes, which suggested more work (J · kg^?1) was performed in Post Acc compared with Pre Acc. Further, ‘possible’ and ‘very likely’ benefits were found for every performance variable for Post Acc compared with Pre Acc, while ‘possible’ benefits were found for Post Acc, compared with Post Acc +PC, for peak power output (W and W · kg^?1). Moderate to strong effect sizes suggested lower core temperatures in both post acclimation trials compared with Pre Acc. Sweat loss was significantly higher (P < 0.05; 23.1%) in Post Acc +PC compared to other trials. In conclusion, no additional performance enhancement was seen when partially acclimated individuals precooled prior to repeat-sprint performance in heat.  相似文献   

Workload and injury incidence in elite football academy players     

Barthélémy Delecroix  Benoit Delaval  Brian Dawson  Serge Berthoin 《Journal of sports sciences》2013,31(24):2768-2773

ABSTRACT

The aim of this study was to prospectively analyse the relationship between workloads and injury in elite football academy players. Elite football academy players (n = 122) from under-19 (U19) and under-21 (U21) of a professional football team competing in UEFA European Cups were followed during 5 seasons. Injuries were collected and absolute workload and workload ratios (4-weeks, 3-weeks, 2-weeks and week-to-week) calculated using a rolling days method with the help of the session Rate of Perceived Exertion. There was no association between absolute workload or workload ratio with the injury incidence in the U19. In the U21, the level of cumulative absolute workloads during 3-weeks (RR = 1.39, p = 0.026) and during 4-weeks (RR = 1.40, p = 0.019) were associated with an increase in injury. There was no association between workload ratio and injury in U21. The significant link between high cumulated 3-weeks and 4 weeks workloads and injury in U21 confirmed the requirement to monitor the internal subjective workload in U21 in order to prevent injury. Further studies exploring the relationships between workload and injury are required in football academy.  相似文献   

Factors associated with minimal changes in countermovement jump performance throughout a competitive division I collegiate basketball season     

Gabriel J. Sanders  Brian Boos  Jessica Rhodes  Roger O. Kollock  Corey A. Peacock  Cory M. Scheadler 《Journal of sports sciences》2013,31(19):2236-2242

ABSTRACT

The purpose of the study was to assess factors that contribute to countermovement jump (CMJ) performance in women’s basketball athletes. Thirteen female athletes participated and were tested for maximal oxygen uptake (VO_2max) and heart rate (HR_max). Athletes were monitored, daily for a total of 21 weeks with heart rate-based wearable devices and CMJ performance and body weight were tested weekly after one day of recovery. 3-jump average height (CMJ_avg), maximum height jump (CMJ_max), and CMJ power (Watts) were calculated and recorded. Playing intensities >85% HR_max, HR_avg, HR_max and training load were averaged for three consecutive days prior to the recovery day. After the season, data was grouped as changes in CMJ power from week one: Large (≤ ?4.39% change), Moderate (?4.4% to ?0.62% change), and Minimal (≥ ?0.61% change) changes. Fixed-effects models revealed a main effect of group (p ≤ 0.05) for CMJ_avg, CMJ_max, VO_2max, weekly percent changes in body weight and for 3-day training load, HR_avg, and playing time at >85% HR_max. When athletes experienced minimal changes in CMJ performance, relative to large changes, they produced greater power, jumped higher, avoided negative changes in weekly body weight, had a greater preseason VO_2max and 3-day average workloads appeared to have an impact on CMJ performance  相似文献   

Information ethics in the context of smart devices     

Brian Roux  Michael Falgoust 《Ethics and Information Technology》2013,15(3):183-194

In this paper, we employ Extended Cognition as a background for a series of thought experiments about privacy and common used information technology devices. Laptops and smart phones are now widely used devices, but current privacy standards do not adequately address the relationship between the owners of these devices and the information stored on them. Law enforcement treats laptops and smart phones are potential sources of information about criminal activity, but this treatment ignores the use of smart devices as extensions of users’ cognitive capability. In Philosophy of Mind, Extended Cognition is a metaphysical theory about the relationship between consciousness or cognitive activity and various external tools or aids that agents employ in the service of cognition. Supporters of Extended Cognition argue that mental activity must be understood as taking place both within the brain and by way of tools such as a logician’s pen and paper, a mathematician’s calculator, or a writer’s word processing program. While Extended Cognition does not have universal support among philosophers of mind, the theory nevertheless describes how agents interact with their “smart devices.” We explore the the implications of taking Extended Cognition seriously with regard to privacy concerns by way of a series of thought experiments. By comparing the differences in expectations of privacy between a citizen and the government, between an employee of a corporate firm, and between citizens alone, we show that expectations of privacy and injury are significantly affected by taking the cognitive role of smart devices into account.  相似文献