Francisco Javier Moreno Hernández

Relationship Between Motor Variability, Accuracy, and Ball Speed in the Tennis Serve

Relationship Between Motor Variability, Accuracy, and Ball Speed in the Tennis Serve 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.

Visual availability, balance performance and movement complexity in dancers

Research regarding the complex fluctuations of postural sway in an upright standing posture has yielded controversial results about the relationship between complexity and the capacity of the system to generate adaptive responses. The aim of this study is to compare the performance and complexity of two groups with different levels of expertise in postural control during a balance task. We examined the balance ability and time varying (dynamic) characteristics in a group of 18 contemporary dancers and 30 non-dancers in different visual conditions. The task involved maintaining balance for 30s on a stability platform with opened or closed eyes. The results showed that dancers exhibited greater balance ability only in open eyes task than non-dancers. We also observed a lower performance in both groups during the test with closed eyes, but only dancers reduced their complexity in closed eyes task. The main conclusion is that the greater postural control exhibited by dancers depends on the availability of visual information.

Variations in task constraints shape emergent performance outcomes and complexity levels in balancing

Abstract This study investigated the extent to which specific interacting constraints of performance might increase or decrease the emergent complexity in a movement system, and whether this could affect the relationship between observed movement variability and the central nervous system’s capacity to adapt to perturbations during balancing. Fifty-two healthy volunteers performed eight trials where different performance constraints were manipulated: task difficulty (three levels) and visual biofeedback conditions (with and without the center of pressure (COP) displacement and a target displayed). Balance performance was assessed using COP-based measures: mean velocity magnitude (MVM) and bivariate variable error (BVE). To assess the complexity of COP, fuzzy entropy (FE) and detrended fluctuation analysis (DFA) were computed. ANOVAs showed that MVM and BVE increased when task difficulty increased. During biofeedback conditions, individuals showed higher MVM but lower BVE at the easiest level of task difficulty. Overall, higher FE and lower DFA values were observed when biofeedback was available. On the other hand, FE reduced and DFA increased as difficulty level increased, in the presence of biofeedback. However, when biofeedback was not available, the opposite trend in FE and DFA values was observed. Regardless of changes to task constraints and the variable investigated, balance performance was positively related to complexity in every condition. Data revealed how specificity of task constraints can result in an increase or decrease in complexity emerging in a neurobiological system during balance performance.

Aprenentatge diferencial aplicat al servei de voleibol en esportistes novells

L’aprenentatge diferencial s’ha mostrat util per a la millora de determinades habilitats motrius. Els resultats en poblacions novelles contrasten amb les recomanacions basades en la practica en condicions de variabilitat o interferencia contextual que questionen la seva utilitat en l’aprenentatge de noves habilitats. En aquest treball es comparen les modificacions de la velocitat i la precisio del servei en voleibol en aplicar les metodologies d’entrenament per consistencia i d’aprenentatge diferencial. Una mostra de 33 participants sense experiencia en voleibol es va dividir en tres grups. Dos grups van dur a terme tres setmanes d’entrenament, mentre que el tercer va conformar el de control. Els participants es van avaluar abans i en dues ocasions posteriors. En cada test es va registrar la precisio i la velocitat dels serveis. Dels resultats es destaca la millora tant en precisio com en velocitat dels grups de practica. A mes a mes, el grup d’entrenament diferencial presenta una milloria en la consistencia de la precisio, de manera que disminueix l’error variable dels seus assajos. La principal conclusio de l’estudi es que la metodologia de l’entrenament diferencial pot ser una metodologia molt eficac per a l’aprenentatge del servei en voleibol en poblacions novelles.