The authors applied algorithms based on the sample entropy (SampEn) measurements to analyze the evolution of regularity in center of pressure displacements on the medialateral (ML) and anteroposterior (AP) axes after the application of 2 balance training methods: differential and traditional. A total of 14 young healthy participants took part in this study undertaking 5 SampEn measurements, a pre- and posttest, and 3 retests on dynamic balance and monopodal support. Results show a SampEn increase in the ML axis over the medium term (4 weeks) with both training methods. Over the short term (1 week), only traditional training shows a SampEn increase in the ML axis. In the AP axis, the traditional training method also shows a SampEn increase over the medium and short terms. A higher irregularity of the COP displacements is also present in the same axis, far from the higher regularity observed in the AP axis. These findings suggest a variability strategy related with the postural control during supports.

The visual behaviour is a determining factor in sailing due to the influence of the environmental conditions. The aim of this research was to determine the visual behaviour pattern in sailors with different practice time in one star race, applying a probabilistic model based on Markov chains. The sample of this study consisted of 20 sailors, distributed in two groups, top ranking (n = 10) and bottom ranking (n = 10), all of them competed in the Optimist Class. An automated system of measurement, which integrates the VSail-Trainer sail simulator and the Eye Tracking System(TM) was used. The variables under consideration were the sequence of fixations and the fixation recurrence time performed on each location by the sailors. The event consisted of one of simulated regatta start, with stable conditions of wind, competitor and sea. Results show that top ranking sailors perform a low recurrence time on relevant locations and higher on irrelevant locations while bottom ranking sailors make a low recurrence time in most of the locations. The visual pattern performed by bottom ranking sailors is focused around two visual pivots, which does not happen in the top ranking sailor's pattern. In conclusion, the Markov chains analysis has allowed knowing the visual behaviour pattern of the top and bottom ranking sailors and its comparison.

This investigation examined the effects of distributed and massed practice on the learning and retention of a discrete computerized skill (Exp. 1) and a continuous computerized skill (Exp. 2). 40 men were randomly assigned to one of four groups, of which two groups took part in Exp. 1 and two groups in Exp. 2. Performance was assessed at various points during acquisition and then on 8 retention tests conducted at varying times after acquisition. Learning curves for practice were highly similar for the two conditions. Participants in the distributed-practice group performed significantly better than those in the massed-practice group at the end of practice on both the discrete and continuous skills. However, participants in the distributed-practice group performed significantly more poorly on retention during 24 hr. and after acquisition. Participants in the massed-practice condition performed significantly better on retention tests than did those who learned in the distributed-practice condition.

The main objective of this study was to analyze the motor variability in the performance of the tennis serve and its relationship to performance outcome. Seventeen male tennis players took part in the research, and they performed 20 serves. Linear and non-linear variability during the hand movement was measured by 3D Motion Tracking. Ball speed was recorded with a sports radar gun and the ball bounces were video recorded to calculate accuracy. The results showed a relationship between the amount of variability and its non-linear structure found in performance of movement and the outcome of the serve. The study also found that movement predictability correlates with performance. An increase in the amount of movement variability could affect the tennis serve performance in a negative way by reducing speed and accuracy of the ball.

The effects of induced variability in the improvement on shot at goal in soccer were examined. The hypothesis tested was that induced variability would be more beneficial for performance than repetition practice; 20 young soccer players (N ¼ 20) trained with induced variability, and 21 (N ¼ 21) trained with repetition method. Accuracy and ball speed were analyzed in three moments: pre-test, post-test carried out after 10 training sessions and re-test, applied at short term (one week). The induced variability group improved the accuracy on post-test (p ¼ 0.005) and re-test (p ¼ 0.0001). The repetition training group improved the accuracy on re-test (p ¼ 0.0001). The ball speed increased in both groups on post-test and re-test (p ¼ 0.0001). The induced variability improves the accuracy of the kicks at end of training, and short term after periods without practice. The repetition practice is effective to perform after no practice time only. The practice in both conditions leads to an increase in the ball speed at end of training as after periods without practice.

This study investigated simultaneous treatments in contextual interference (blocked and random practice) and their effect on the process of learning four tennis shots. 8 tennis players participated in the research, which was carried out in two phases. The first phase involved a 3-wk. period of 12 sessions with 192 practice tennis shots per session for each tennis player. The second phase comprised 4 retention tests carried out at 48 hr. and 2, 4, and 6 weeks following the learning phase. This phase consisted of evaluating the retention of the skills that had been practiced during the learning phase. The results indicated an improvement in the quality of shots for both practice conditions during the learning phase. Differences in retention appeared relative to differences in the type of practice conditions (random or blocked) in which the skill was learned and also depended on the type of shot and the time that had elapsed since the learning period.

In a sport conditioned by natural elements such as sailing, visual perception is a key factor for the performance. Research has shown that the visual behavior of athletes at different skill levels varies, which may cause differences in the performance achieved. The aim of this research was to examine the visual behavior of sailors from different ranking positions at the start of a race in a simulated situation. Twenty junior sailors (N = 10 top and N = 10 bottom ranking) participated in this study. The visual behavior was recorded at the start of a sailing simulation. The top-ranking sailors performed more visual fixations on the locations that have more highly relevant information, such as "telltales" and "rivals," than do bottom-ranking sailors (p < .005). The top-ranking sailors are closer to the start line at the time of the start signal. The analysis of the visual search strategy shows that top-ranking sailors employed a more active visual search strategy. More experienced athletes can make better use of the information obtained from the important locations.

The aims of the present study were: to review, identify and analyse the research studies which have investigated the influential factors in sailing performance and to determine which of them are most important. The data were obtained from an analysis carried out in ten different databases, using the words "sail", "sailing", and "sailor" as search descriptors in scientific articles. The search included those articles that contain these key words in the title or abstract, limiting the investigation to the period between 1950 and 2011. The articles analysed in this review were those regarding physical, tactical, technical, psychological, and decision-making characteristics of sailors which directly affect their performance. From the analysed articles, 54% refer to physical characteristics, which were the most studied factor, followed by technique at 22% and decision making at 14%. Strategy (5%) and psychology (3%) are the two aspects that were least investigated. In conclusion, sailors from each sailing class need different physical and/or physiological features. In competitive sailing there are different types of boats that demand various types of effort by the sailor, which is why knowledge of their specific physical and physiological features for each type of vessel is necessary. Apart from the differences in conditional physical abilities needed for each type, there are other determining factors for performance in this sport, such as stimuli perception and decision making, which are considered to a lesser degree in the analysed studies.