Validación de la activación muscular de las extremidades inferiores estimada mediante modelado musculoesquelético y electromiografía en el topspin de derecha y revés del tenis de mesa

This study aimed to validate the lower limb muscle activation, estimated using static optimization against electromyography (EMG), in the topspin forehand and backhand strokes. The secondary purpose was to compare the estimated activations of the major muscles/muscle groups between the forehand and backhand strokes. Eight male college table tennis players hit the cross-court topspin forehands and backhands with maximum effort. Stroke motions and ground reaction forces were measured using a motion capture system and two force plates. The EMG signals of the 16 lower-limb muscles were recorded using a wireless EMG system. The static optimization algorithm of OpenSim was applied to stroke motions to estimate lower limb muscle activation, which was compared to EMG activation. Of the seven muscles that showed maximum activation > 0.3 during the forehand, five showed a Pearson correlation coefficient > 0.3 Of the four muscles that showed maximum activation > 0.3 during the backhand, all four showed a Pearson correlation coefficient >0.3. However, some muscles, such as the bilateral gluteus medius muscles, showed a low correlation between estimated and EMG activation. A possible cause is the co-contraction of the relevant muscles. Concordance correlation coefficients were smaller than their respective Pearson correlation coefficients. This result reflects that EMG envelope (activation) is also an estimate of muscle activation and is subject to noise and confounding factors. Comparisons with additional independent measurements, such as ultrasound muscle images and instrumented joint loading, are necessary for more robust validation of the musculoskeletal modeling and muscle activation. The gluteus maximus and hamstrings on the playing side, and rectus femoris on the non-playing side exhibited higher activation during the forehand than during the backhand. The overall results suggest that the static optimization algorithm can adequately estimate lower-limb muscle activity during the topspin forehand and backhand strokes.El objetivo de este estudio fue validar la activación muscular de las extremidades inferiores estimada mediante optimización estática y electromiografía (EMG) en el topspin de derecha y revés. El objetivo secundario fue comparar las activaciones estimadas de los principales grupos musculares entre los golpes de derecha y revés. Ocho jugadores hombre universitarios de tenis de mesa realizaron con el máximo esfuerzo los golpes topspin de derecha y revés cruzados en la pista. Los movimientos de los golpes y las fuerzas de reacción del suelo fueron medidos con un sistema de captura del movimiento y dos placas de fuerza. Las señales EMG de los músculos de los 16 miembros inferiores fueron grabadas con un sistema EMG inalámbrico. Se usó el algoritmo de optimización estática OpenSim para estimar la activación muscular de los miembros inferiores durante los golpes, y luego se compararon los resultados con la activación de la EMG. De los siete músculos que mostraron activación máxima > 0,3 en el golpe de derecha, cinco mostraron un coeficiente de correlación de Pearson > 0,3. De los cuatro músculos que mostraron activación máxima > 0,3 durante el golpe de revés, los cuatro mostraron un coeficiente de correlación de Pearson > 0,3. Sin embargo, algunos músculos, como el glúteo medio, mostraron una baja correlación entre la activación estimada y la EMG. Una posible causa es la cocontracción de los músculos involucrados.  Los coeficientes de correlación de concordancia fueron menores que sus respectivos coeficientes de correlación de Pearson. Este resultado refleja que la envolvente (activación) de la EMG es también una estimación de la activación muscular y está sujeta a ruido y factores de confusión. Es necesario realizar comparaciones con otras mediciones independientes, como las imágenes musculares por ultrasonido y la carga articular con instrumentos, para lograr una validación más sólida del modelado musculoesquelético y la activación muscular. El glúteo mayor y los isquiotibiales en el lado de juego, y el recto femoral en el lado de no juego, mostraron una mayor activación durante el golpe de derecha que durante el revés. Los resultados generales sugieren que el algoritmo de optimización estática puede estimar adecuadamente la actividad muscular de las extremidades inferiores durante el topspin de derecha y revés

The neuromuscular determinants of unilateral jump performance in soccer players are direction-specific

Purpose: To investigate differences in neuromuscular factors between elite and non-elite players, and to establish which factors underpin direction-specific unilateral jump performance. Methods: Elite (n=23; age, 18.1 ± 1.0 yrs; BMI, 23.1 ± 1.8 kg/m2) and non-elite (n=20; age, 22.3 ± 2.7 yrs; BMI, 23.8 ± 1.8 kg/m2) soccer players performed three unilateral countermovement jumps (CMJs) on a force platform in the vertical, horizontal-forward and medial directions. Knee extension isometric maximum voluntary contraction (iMVC) torque was assessed using isokinetic dynamometry. Vastus lateralis fascicle length and angle of pennation (AoP), and quadriceps femoris muscle volume (Mvol) and physiological cross sectional area (PCSA) were assessed using ultrasonography. Vastus lateralis activation was assessed via electromyography. Results: Elite soccer players presented greater knee extensor iMVC torque (365.7±66.6 vs. 320.1±62.6 N·m; P=0.045), Mvol (2853±508 vs. 2429±232 cm3, P=0.001) and PCSA (227±42 vs. 193±25 cm2, P=0.003) than non-elite. In both cohorts, unilateral vertical and unilateral medial CMJ performance correlated with Mvol and PCSA (r≥0.310 P≤0.043). In elite soccer players, unilateral vertical and unilateral medial CMJ performance correlated with upward phase vastus lateralis activation, and AoP (r≥0.478, P≤0.028). Unilateral horizontal-forward CMJ peak vertical power did not correlate with any measure of muscle size or activation but correlated inversely with AoP (r=-0.413; P=0.037). Conclusions: Whilst larger and stronger quadriceps differentiated elite from non-elite players, relationships between neuromuscular factors and unilateral jump performance were shown to be direction-specific. These findings support a notion that improving direction-specific muscular power in soccer requires improving a distinct neuromuscular profile

VARIABILITY OF RELEASE PARAMETERS IN BASKETBALL FREE THROW

The aim of this study is to clarify what kind of variability of release parameters is associated with shot accuracy in basketball free-throw. Eight male right-handed basketball players in college team participated in this study. Participants made 50 shots from the free-throw line after warm-up. A 16-camera motion capture system was used to record the coordinates of the reflective markers attached on the participants’ bodies and the ball. The ball release parameters (i.e. release speed, angle and position) were calculated for the ball at the time of release. TNC-analysis that quantifies Tolerance, Noise, and Covariation cost of a performance (Cohen & Sternad, 2009; Sternad et al., 2011) and a correlation analysis were used to analyse the variability of release parameters. Our results showed that the value of C-cost is smaller for the participant whose shot probability of success was high. Our results suggest that learning various patterns of success in training may be efficient for improvement in free-throw

EFFECT OF MECHANICAL PROPERTIES OF THE LOWER LIMB MUSCLES ON MUSCULAR EFFORT DURING TABLE TENNIS FOREHAND

The purpose of this study was to investigate the effect of the maximum isometric forces and the maximum shortening velocities of the lower limb muscles on the muscular effort during the table tennis forehand. Four male collegiate players performed table tennis forehand drives with maximum effort. We used OpenSim’s static optimization algorithm to estimate the activation patterns of lower limb muscles. The cost function was the sum of squared muscle activations for all lower limb muscles, which we will refer to as the muscular effort. The simulations were repeated with the maximum isometric forces or the maximum shortening velocities of each muscle group changed by ±10% of their original values. The results suggest that increasing the maximum isometric forces of the hip extensors and adductors may be most effective to reduce the muscular effort

EFFECTS OF SEGMENTAL ROTATIONS ON VERTICAL AND HORIZONTAL ENERGIES DURING TAKE-OFF OF A LONG JUMP

This study aimed to reveal the effect of segmental rotation on the generation of vertical velocity and loss of horizontal velocity during take-off of a long jump. 3D motion capture system and force plates were used to capture the long jumps by nine male athletes with an approach running distance of approximately 20 m. Forward rotations of the shank and thigh of the stance leg increased vertical energy (Evert) and decreased horizontal energy (Ehori); however, elevation of the free leg side of the pelvis increased Evert (0.53 ± 0.16 J/kg), although pelvic elevation did not decrease Ehori (0.01 ± 0.02 J/kg). It was revealed that although shank and thigh movements involved the loss of horizontal velocity, elevation of the free leg side of the pelvis generated vertical velocity without the loss of horizontal velocity. This study provides evidence for a new technical approach for a long jump

UNCONTROLLED MANIFOLD ANALYSIS OF JOINT ANGLE VARIABILITY DURING TABLE TENNIS FOREHAND

The purpose of this study was to evaluate the variance structure of the trunk and racket arm joint angles in the table tennis topspin forehand in relation to the control of racket orientation using the uncontrolled manifold (UCM) approach. Seventeen (9 advanced and 8 intermediate) male collegiate table tennis players performed the strokes against backspin. The UCM analysis was conducted using 30 trial data per each participant. The degree of redundancy exploitation to stabilize the racket vertical and horizontal angles were not significantly different between the two performance levels, suggesting that the ability to exploit joint configuration redundancy may not contribute to achieving higher performance in sport hitting skill. The degree of redundancy exploitation is highest at ball impact and this result may reflect that the table tennis forehand is a fast interceptive task

Optimal coordination of maximal-effort horizontal and vertical jump motions – a computer simulation study

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to investigate the coordination strategy of maximal-effort horizontal jumping in comparison with vertical jumping, using the methodology of computer simulation.</p> <p>Methods</p> <p>A skeletal model that has nine rigid body segments and twenty degrees of freedom was developed. Thirty-two Hill-type lower limb muscles were attached to the model. The excitation-contraction dynamics of the contractile element, the tissues around the joints to limit the joint range of motion, as well as the foot-ground interaction were implemented. Simulations were initiated from an identical standing posture for both motions. Optimal pattern of the activation input signal was searched through numerical optimization. For the horizontal jumping, the goal was to maximize the horizontal distance traveled by the body's center of mass. For the vertical jumping, the goal was to maximize the height reached by the body's center of mass.</p> <p>Results</p> <p>As a result, it was found that the hip joint was utilized more vigorously in the horizontal jumping than in the vertical jumping. The muscles that have a function of joint flexion such as the m. iliopsoas, m. rectus femoris and m. tibialis anterior were activated to a greater level during the countermovement in the horizontal jumping with an effect of moving the body's center of mass in the forward direction. Muscular work was transferred to the mechanical energy of the body's center of mass more effectively in the horizontal jump, which resulted in a greater energy gain of the body's center of mass throughout the motion.</p> <p>Conclusion</p> <p>These differences in the optimal coordination strategy seem to be caused from the requirement that the body's center of mass needs to be located above the feet in a vertical jumping, whereas this requirement is not so strict in a horizontal jumping.</p

INFLUENCE OF TURN RADIUS OF RUNNING ON TORSIONAL LOADING OF THE TIBIA

The purpose of this study was to investigate influence of turn radius of running on the torsional loading of the tibia. Six male subjects ran on a straightway and anti-clockwise corners with different turn radiuses (R=15m and 5m). Data were collected using two high-speed cameras and force platforms. The torsional stresses acting on the inner tibias of runners were compared among each running condition. At beginning, net torsional moments at both ends of the lower leg were calculated. Then, the tibial torsional stresses were estimated, based on equilibrium of those moments. Much larger torsional stress acted on the tibia in later portion of the stance phase of sharper cornering compared to other two running conditions. Mean value of the maximum stress in sharper cornering was also significantly larger (