Worldwide variation in the performance of children and adolescents: An analysis of 109 studies of the 20-m shuttle run test in 37 countries

Abstract

This study is a meta-analysis of 109 reports of the performance of children and adolescents on the 20-m shuttle run test (20-mSRT). The studies were performed in 37 countries and included data on 418,026 children, tested between 1981 and 2003. Results were expressed as running speed (km · h^?1) at the final completed stage of the 20-mSRT. Raw data were combined with pseudodata using Monte Carlo simulation. The 20-mSRT performances were expressed as z-scores relative to all children of the same age and sex from all countries. An overall “performance index” was derived for each country as the average of the age- and sex-specific z-scores for all children from that country. Factorial analysis of variance was used to compare scores among countries and regions, and between boys and girls of the same age. There was wide and significant (P < 0.0001) global variability in the performance of children. The best performing children were from the Northern European countries Estonia, Iceland, Lithuania, and Finland (0.6 – 0.9 standard deviations above the global average). The worst performing children were from Singapore, Brazil, USA, Italy, Portugal, and Greece (0.4 – 0.9 standard deviations below the global average). There is evidence that performance was negatively related to being overweight, as well as to a country's average temperature.     

Relationships between training load,injury, and fitness in sub-elite collision sport athletes

Abstract

The purpose of this study was to develop statistical models that estimate the influence of training load on training injury and physical fitness in collision sport athletes. The incidence of training injuries was studied in 183 rugby league players over two competitive seasons. Participants were assessed for height, body mass, skinfold thickness, vertical jump, 10-m, 20-m and 40-m sprint time, agility, and estimated maximal aerobic power in the off-season, pre-season, mid-season, and end-season. Training load and injury data were summarised into pre-season, early-competition, and late-competition training phases. Individual training load, fitness, and injury data were modelled using a logistic regression model with a binomial distribution and logit link function, while team training load and injury data were modelled using a linear regression model. While physical fitness improved with training, there was no association (P = 0.16 – 0.99) between training load and changes in physical fitness during any of the training phases. However, increases in training load during the early-competition training phase decreased (P = 0.04) agility performance. A relationship (P = 0.01 – 0.04) was observed between the log of training load and odds of injury during each training phase, resulting in a 1.50 – 2.85 increase in the odds of injury for each arbitrary unit increase in training load. Furthermore, during the pre-season training phase there was a relationship (P = 0.01) between training load and injury incidence within the training load range of 155 and 590 arbitrary units. During the early and late-competition training phases, increases in training load of 175 – 620 arbitrary units and 145 – 410 arbitrary units, respectively, resulted in no further increase in injury incidence. These findings demonstrate that increases in training load, particularly during the pre-season training phase, increase the odds of injury in collision sport athletes. However, while increases in training load from 175 to 620 arbitrary units during the early-competition training phase result in no further increase in injury incidence, marked reductions in agility performances can occur. These findings suggest that reductions in training load during the early-competition training phase can reduce the odds of injury without compromising agility performances in collision sport athletes.     

Use of dual-task methodology for skill assessment and development: Examples from rugby league

Abstract

We assessed the attentional demands of drawing and passing in rugby league players and investigated the effects of single-task and dual-task training on the acquisition, retention, and transfer of skill in these athletes. In Study 1, high-skilled and lesser-skilled rugby league players performed a standardized 2-on-1 drill under single-task (primary skill in isolation) and dual-task (primary skill while performing a secondary verbal tone recognition task) conditions. No differences were detected in primary task performance between groups, although the performance of the high-skilled players was more resistant to skill decrement under dual-task conditions. In Study 2, high-performance rugby league players were randomly allocated to either a single-task or dual-task training group. Each group underwent 8 weeks of training between the pre- and post-test sessions. While the mean improvement for draw and pass proficiency under dual-task conditions in the dual-task training group was greater than in the single-task training group (10.0% vs. 2.3%), the differences, while providing a moderate effect size (d = 0.57), were not statistically significant. These results suggest that the attentional demands of drawing and passing are reduced in high-skilled rugby league players compared with their lesser-skilled counterparts. In addition, compared with single-task training, dual-task training appears to improve the ability to perform dual-task draw and pass tasks (possibly through an improvement in time-sharing skills). Further studies are required to verify the efficacy of dual-task training as a training stimulus.     

Biomechanical Effects of Fatigue on 10,000 Meter Running Technique

Abstract

A study of the effect of fatigue on the mechanical characteristics of running during a 10,000 meter race was undertaken using high speed cinematography and a computer analysis technique. Eight highly skilled male subjects were filmed at four intervals throughout the event. An analysis of variance for trends was conducted for each of the dependent variables indicating the adjustments made by the runners that accompanied fatigue over the four stages of the event. Runners countered fatigue by changing sections of their total gait pattern (stride length, stride rate, segmental body positions) and reducing running velocity. Toward the end of the race the runners became less competent in the positioning of the foot and leg at foot-strike, which increased the potential for a retarding effect. A more extended lower limb increased the energy requirements of the recovery phase during the latter stages of the race. Fatigue caused these highly skilled runners to systematically alter their technique throughout the race. These adjustments, however, were not excessive.     

There Is an “I” in TEAM

Abstract

We investigated narcissism as a moderator of social loafing on a physical performance task. High and low narcissistic individuals twice performed a cycling task in same-sex teams of three: once when identifiability was low; and once when identifiability was high. A significant interaction between narcissism and identifiability was revealed, F(1, 40) = 4.09, p < .05, η² = .09 for performance. Follow-up tests indicated that high narcissists' performance significantly increased with greater identifiability, whereas low narcissists displayed no such performance differences. Results suggested that this effect was due to an increase in narcissists' on-task effort (ratings of perceived exertion and heart rate) when they knew that their performance was to be identified.     

Modifying Equipment in Early Skill Development: A Tennis Perspective

Purpose: The International Tennis Federation recently launched a worldwide campaign advocating the use of equipment scaling for children learning to play tennis. The aim of this study was to investigate the influence that varying racquet sizes and ball compressions had on children's ability to play a forehand groundstroke. Method: This was a quantitative repeated-measures design experiment. Children were required to perform a forehand hitting task using each of 9 combinations of tennis racquets and balls (i.e., 3 racquet sizes × 3 ball compressions). Children's hitting performance was measured using a points system. The aim for the children was to score as many points as possible. Hitting technique was measured via video replay. Results: Hitting performance was best when the smallest racquet combined with the ball with the least compression was used. The ball with the least compression also promoted 2 technique benefits: swinging the racquet from low to high and striking the ball in front and to the side of the body. Conclusions: This study demonstrated the benefits for young children playing with scaled racquets and low-compression balls. The findings are discussed with regards to their relevance to theories of skill acquisition.     

Straight sprinting is the most frequent action in goal situations in professional football

The present study aimed to analyse the influence of speed and power abilities in goal situations in professional football. During the second half of the season 2007/08, videos of 360 goals in the first German national league were analysed by visual inspection. For the assisting and the scoring player the situations immediately preceding the goal were evaluated. The observed actions were categorised as: no powerful action, rotation (around the body's centre-line), straight sprint, change-in-direction sprint, jump, or a combination of those categories. Two hundred and ninety-eight (83%) goals were preceded by at least one powerful action of the scoring or the assisting player. Most actions for the scoring player were straight sprints (n = 161, 45% of all analysed goals, P < 0.001) followed by jumps (n = 57, 16%), rotations and change-in-direction sprints (n = 22, 6% each). Most sprints were conducted without an opponent (n = 109, P < 0.001) and without the ball (n = 121, P < 0.001). Similarly, for the assisting player the most frequent action was a straight sprint (n = 137, P < 0.001) followed by rotations (n = 28), jumps (n = 22) and change-in-direction sprints (n = 18). The straight sprints were mostly conducted with the ball (n = 93, P = 0.003). In conclusion, straight sprinting is the most frequent action in goal situations. Power and speed abilities are important within decisive situations in professional football and, thus, should be included in fitness testing and training.     

Skill qualities as risk factors for contact injury in professional rugby league players

Abstract We investigated the relationship between skill qualities and contact injury risk in professional rugby league players. Sixty-six professional rugby league players aged 23?±?4 years (mean?±?s) participated in this three-year prospective study. Players underwent assessments of tackling proficiency, dual-task draw-and-pass proficiency, reactive agility, pattern recall, and pattern prediction. The frailty model was applied to calculate the adjusted risk ratios of injury. When the players' age and playing position were adjusted in the frailty model, the risk ratios showed that reactive agility was a predictor for the risk of injury. Players with reactive agility decision times of >80?ms had a lower incidence (relative risk?=?0.68, 95% CI 0.47-0.98, P?=?0.04) of injuries than players with reactive agility decision times of ≤80 ms. Although there was no relationship between injury and the majority of skill qualities (P?=?0.47-0.93), players with poor reactive agility performances (specifically longer decision times) had a lower risk of injury, suggesting that poor perceptual skill is protective against contact injuries in professional rugby league players. These players might inadvertently avoid the heavy collisions that result in injury, or at best result in partial contact that does not result in exposure to the full force of a tackle.     

Body composition and hydration status changes in male and female open-water swimmers during an ultra-endurance event

Body mass changes during ultra-endurance performances have been described for running, cycling and for swimming in a heated pool. The present field study of 20 male and 11 female open-water swimmers investigated the changes in body composition and hydration status during an ultra-endurance event. Body mass, both estimated fat mass and skeletal muscle mass, haematocrit, plasma sodium concentration ([Na+]) and urine specific gravity were determined. Energy intake, energy expenditure and fluid intake were estimated. Males experienced significant reductions in body mass (-0.5 %) and skeletal muscle mass (-1.1 %) (P < 0.05) during the race compared to females who showed no significant changes with regard to these variables (P > 0.05). Changes in percent body fat, fat mass, and fat-free mass were heterogeneous and did not reach statistical significance (P > 0.05) between gender groups. Fluid intake relative to plasma volume was higher in females than in males during the ultra-endurance event. Compared to males, females' average increase in haematocrit was 3.3 percentage points (pp) higher, urine specific gravity decrease 0.1 pp smaller, and plasma [Na+] 1.3 pp higher. The observed patterns of fluid intake, changes in plasma volume, urine specific gravity, and plasma [Na+] suggest that, particularly in females, a combination of fluid shift from blood vessels to interstitial tissue, facilitated by skeletal muscle damage, as well as exercise-associated hyponatremia had occurred. To summarise, changes in body composition and hydration status are different in male compared to female open-water ultra-endurance swimmers.