Impact forces and neck muscle activity in heading by collegiate female soccer players

Three soccer header types (shooting, clearing and passing) and two heading approaches (standing and jumping) were manipulated to quantify impact forces and neck muscle activity in elite female soccer players. The 15 participants were Division I intercollegiate soccer players. Impact forces were measured by a 15-sensor pressure array secured on the forehead. The electromyographic (EMG) activity of the left and right sternocleidomastoid and trapezius muscles was recorded using surface electrodes. Maximum impact forces and impulses as well as the EMG data were analysed with separate repeated-measures analyses of variance. Impact forces and impulses did not differ among the header types or approaches. Higher values were found for jumping versus standing headers in the mean normalized EMG for the right sternocleidomastoid. In addition, the integrated EMG was greater for the right sternocleidomastoid and right and left trapezius (P < 0.05). The sternocleidomastoid became active earlier than the trapezius and showed greater activity before ball contact. The trapezius became active just before ball contact and showed greater activity after ball contact. The increased muscle activity observed in the neck during the jumping approach appears to stabilize the connection between the head and body, thereby increasing the stability of the head-neck complex.     

Severity and cost of injuries in amateur rugby league: a case study

The aim of this study was to determine the severity and cost of injuries in amateur rugby league. Seventy-two amateur rugby league players aged 28 +/- 6 years (mean +/- s) were surveyed at the end of a competitive season. An injury was defined as any pain, disability or injury that occurred as a result of a competition game which caused the player to miss subsequent games. Injuries were classified as minor (one game missed), moderate (two to four games missed) and major (five or more games missed). Of the 72 questionnaires distributed, 34 (47.2%) were returned. Twenty respondents (58.8%) sustained an injury that resulted in one or more missed games. Eight injured players (40.0%) missed five or more training sessions, six of whom (30%) missed five or more games as a result of the injury. The median time lost from employment or study for all injured players was 2 days per playing injury. The respective median direct (e.g. medical expenses) and indirect (e.g. wages lost) costs associated with the injury were 28.29 pounds and 77.04 pound per playing injury. A considerable proportion of injuries sustained in the present sample of amateur rugby league players were major, resulting in a loss of training, playing and employment or study time, and these injuries were associated with significant direct and indirect economic costs. Further studies, using a larger sample, would complement the present findings in establishing the severity and cost of amateur rugby league injuries. These results suggest that prevention strategies are required to reduce the severity and cost of amateur rugby league injuries.     

Effects of active, passive or no warm-up on metabolism and performance during high-intensity exercise

The aim of this study was to determine the influence of type of warm-up on metabolism and performance during high-intensity exercise. Eight males performed 30 s of intense exercise at 120% of their maximal power output followed, 1 min later, by a performance cycle to exhaustion, again at 120% of maximal power output. Exercise was preceded by active, passive or no warm-up (control). Muscle temperature, immediately before exercise, was significantly elevated after active and passive warm-ups compared to the control condition (36.9 +/- 0.18 degrees C, 36.8 +/- 0.18 degrees C and 33.6 +/- 0.25 degrees C respectively; mean +/- sx) (P< 0.05). Total oxygen consumption during the 30 s exercise bout was significantly greater in the active and passive warm-up trials than in the control trial (1017 +/- 22, 943 +/- 53 and 838 +/- 45 ml O2 respectively). Active warm-up resulted in a blunted blood lactate response during high-intensity exercise compared to the passive and control trials (change = 5.53 +/- 0.52, 8.09 +/- 0.57 and 7.90 +/- 0.38 mmol x l(-1) respectively) (P < 0.05). There was no difference in exercise time to exhaustion between the active, passive and control trials (43.9 +/- 4.1, 48.3 +/- 2.7 and 46.9 +/- 6.2 s respectively) (P= 0.69). These results indicate that, although the mechanism by which muscle temperature is elevated influences certain metabolic responses during subsequent high-intensity exercise, cycling performance is not significantly affected.     

The Dutch motor skills assessment as tool for talent development in table tennis: a reproducibility and validity study

A motor skills assessment could be helpful in talent development by estimating essential perceptuo-motor skills of young players, which are considered requisite to develop excellent technical and tactical qualities. The Netherlands Table Tennis Association uses a motor skills assessment in their talent development programme consisting of eight items measuring perceptuo-motor skills specific to table tennis under varying conditions. This study aimed to investigate this assessment regarding its reproducibility, internal consistency, underlying dimensions and concurrent validity in 113 young table tennis players (6–10 years). Intraclass correlation coefficients of six test items met the criteria of 0.7 with coefficients of variation between 3% and 8%. Cronbach’s alpha valued 0.853 for internal consistency. The principal components analysis distinguished two conceptually meaningful factors: “ball control” and “gross motor function.” Concurrent validity analyses demonstrated moderate associations between the motor skills assessment’s results and national ranking; boys r = ?0.53 (P < 0.001) and girls r = ?0.45 (P = 0.015). In conclusion, this evaluation demonstrated six test items with acceptable reproducibility, good internal consistency and good prospects for validity. Two test items need revision to upgrade reproducibility. Since the motor skills assessment seems to be a reproducible, objective part of a talent development programme, more longitudinal studies are required to investigate its predictive validity.     

The effect of l-citrulline and watermelon juice supplementation on anaerobic and aerobic exercise performance

Citrulline has been proposed as an ergogenic aid, leading to an interest in watermelon given its high citrulline concentration. The aim of this study was to determine the effects of a single, pre-exercise dose of l-citrulline, watermelon juice, or a placebo on the total maximum number of repetitions completed over 5 sets, time to exhaustion, maximal oxygen consumption (VO₂max), anaerobic threshold, and flow-mediated vasodilation. A randomised double-blind within-participants study design was used to examine these effects among 22 participants (n = 11 males). Supplementation included either a 7.5% sucrose drink containing 6 g of l-citrulline, 710 mL of watermelon juice (~1.0 g citrulline), or a 7.5% sucrose placebo drink. Supplementation was administered 1 or 2 h before exercise testing to investigate a timing effect. There was no significant effect between the three supplements for the total number of repetitions, time to exhaustion, VO₂max, anaerobic threshold, or flow-mediated vasodilation. There was also no interaction observed relative to gender or supplement timing (P > 0.05). A single dose of l-citrulline or watermelon juice as a pre-exercise supplement appears to be ineffective in improving exercise performance; however, greater doses of l-citrulline have been shown to be safe and are currently left unexamined.     

The use of spatial manipulation to examine goalkeepers’ anticipation

This study investigated whether anticipation and search strategies of goalkeepers are influenced by temporally and spatially manipulated video of a penalty. Participants were clustered into three groups depending on skill: goalkeepers (n = 17), field players (n = 20) and control group (n = 20). An eye tracker was worn whilst watching 40 videos of a striker kicking to four corners of a goal in random order. All 40 videos were temporally occluded at foot-to-ball contact, and the non-kicking leg of 20 videos was spatially manipulated. Results showed that goalkeepers had significantly better predictions than the two groups with no differences between the two testing conditions. According to effect size, the percentage of fixation location and viewing time of the kicking leg and ball were greater for the goalkeepers and field players group than the control group irrespective of testing conditions. The fixations on the kicking leg and ball in conjunction with comparable predictions between spatially manipulated and control conditions suggest that goalkeepers may not rely on the non-kicking leg. Furthermore, goalkeepers appear to use a global perceptual approach by anchoring on a distal fixation point/s of the penalty taker whilst using peripheral vision to obtain additional information.     

eSport: Vom Präfix zum Thema für den organisierten Sport!?

In an increasingly differentiated culture of movement, play and sport as well as a more and more digitized society, the topic of eSports has been intensively discussed in recent time. The objective-categorical basics of the discussion seem to be clear only at first sight. A closer look points to the need of a differentiated cross-disciplinary discussion of the topic. It becomes clear that above all the underlying understanding of sport, the content-related demarcation as well as the social positioning contribute decisively to the perception of eSport (approval/rejection). The present article takes up the discussion with reference to the heterogeneity, heteronomy and complexity of sports and provides an alternative interpretive idea on the topic.     

Evaluations of matrix functions by real similarity transformation

An effective way of constructing transforming matrix which similarly transforms a real square matrix to a quasi-diagonal form, is obtained. The transforming matrix as well as the quasi-diagonal form are real, regardless whether the given matrix has real eigenvalues or not. Formulas are included; they can be applied conveniently to evaluate a matrix function f(A) from the given scalar function f(λ). Three examples are given to illustrate the ease of application. These are the solutions of system differential equations of first and second order, and the determination of Nth root of a square matrix.     

Medical writing: should you add to it?

Suggests some reasons for the growth in the number of medical papers published, and some disadvantages arising from it.