Effects of 8-weeks of stable vs unstable surface destabilizing training on shot outcome in elite golfers (Efectos de 8 semanas de entrenamiento desestabilizador en superficies estables vs inestables sobre el resultado de los golpes en golfistas de élite)

Purpose: This research aimed to compare the effect of two intervention programs using stable or unstable surfaces on speed and hitting distance in golf stroke/swing. Methods: Twenty-five elite golfers (19.20 ± 1.77 years, height = 181.12 ± 4 cm, body mass = 75.35 ± 5.83; kg, BMI = 22.71 ± 1.76 kg.m2, handicap: 2.49 ± 2.56) were randomly assigned to two different 8-week training programs based on unstable surface (n = 12) or stable surface training (n=13). Measurements of carry distance and club head speed were performed using the Trackman Golf® system, with each participant executing five swings and obtaining the average and best distance. Results: No significant changes (p< 0.05) in the club head speed or carry distance were found after the intervention in the stable surface or the unstable surface training group. Conclusions: The proposed intervention using instability surfaces does not provide any additional benefit to training on stable surfaces in the specific performance of the stroke in elite golfers. Resumen. Objetivo: Esta investigación tuvo como objetivo comparar el efecto de dos programas de intervención que utilizan superficies estables o inestables sobre la velocidad y la distancia de golpeo en el golpeo/swing de golf. Métodos: Veinticinco golfistas de élite (19,20 ± 1,77 años, altura = 181,12 ± 4 cm, peso corporal = 75,35 ± 5,83; kg, IMC = 22,71 ± 1,76 kg.m2, hándicap: 2,49 ± 2,56) fueron asignados aleatoriamente a dos programas de entrenamiento diferentes de 8 semanas de duración basados en superficies inestables (n = 12) o en superficies estables (n = 13). Las mediciones de la distancia de golpeo y la velocidad de la cabeza del palo se realizaron con el sistema Trackman Golf®, ejecutando cada participante cinco swings y obteniendo la media y la mejor distancia. Resultados: No se encontraron cambios significativos (p< 0,05) en la velocidad de la cabeza del palo ni en la distancia de golpeo después de la intervención en el grupo de entrenamiento en superficie estable o en el de superficie inestable. Conclusiones: La intervención propuesta utilizando superficies de inestabilidad no aporta ningún beneficio adicional al entrenamiento en superficies estables en el rendimiento específico del golpe en golfistas de élite.

The Effect of Cognitive Task on Postural Control Dynamic Regularity of Athletes With Chronic Ankle Instability When Standing on an Unstable Surface

Background and Objectives: Postural control disorder is a common complication in patients with Chronic Ankle Instability (CAI). The present study aimed to investigate the effect of dual cognitive task on postural control behavior with regard to the Center of Pressure (CoP) signal regularity while standing on an unstable surface in athletes with CAI. Methods: In the present study, 58 men participated in two groups of healthy and patients with CAI. The CoP signal was examined in 4 different unstable states on the wobble board located at the center of the force plate. The regularity of the signals recorded from the force plate was investigated using sample entropy in two directions: anterior-posterior and medial-lateral. Results: In both groups, there was a significant difference in CoP’s sample entropy signal when performing a cognitive task with a postural task (P<0.001). There was a significant difference between the two groups in the cognitive task and the single task in the anteroposterior direction while standing on two legs. Conclusion: During dual tasks, the patients with CAI have a more dynamic regularity in the CoP signal than their normal counterparts. In the dual-task condition, more irregularities are observed in the CoP signal of healthy individuals. In unstable conditions, patients with CAI decrease the adaptability of postural control behavior with increasing CoP signal regularity.

Proactive Modulation in the Spatiotemporal Structure of Muscle Synergies Minimizes Reactive Responses in Perturbed Landings

Stability training in the presence of perturbations is an effective means of increasing muscle strength, improving reactive balance performance, and reducing fall risk. We investigated the effects of perturbations induced by an unstable surface during single-leg landings on the mechanical loading and modular organization of the leg muscles. We hypothesized a modulation of neuromotor control when landing on the unstable surface, resulting in an increase of leg muscle loading. Fourteen healthy adults performed 50 single-leg landings from a 30 cm height onto two ground configurations: stable solid ground (SG) and unstable foam pads (UG). Ground reaction force, joint kinematics, and electromyographic activity of 13 muscles of the landing leg were measured. Resultant joint moments were calculated using inverse dynamics and muscle synergies with their time-dependent (motor primitives) and time-independent (motor modules) components were extracted via non-negative matrix factorization. Three synergies related to the touchdown, weight acceptance, and stabilization phase of landing were found for both SG and UG. When compared with SG, the motor primitive of the touchdown synergy was wider in UG (p &lt; 0.001). Furthermore, in UG the contribution of gluteus medius increased (p = 0.015) and of gastrocnemius lateralis decreased (p &lt; 0.001) in the touchdown synergy. Weight acceptance and stabilization did not show any statistically significant differences between the two landing conditions. The maximum ankle and hip joint moment as well as the rate of ankle, knee, and hip joint moment development were significantly lower (p &lt; 0.05) in the UG condition. The spatiotemporal modifications of the touchdown synergy in the UG condition highlight proactive adjustments in the neuromotor control of landings, which preserve reactive adjustments during the weight acceptance and stabilization synergies. Furthermore, the performed proactive control in combination with the viscoelastic properties of the soft surface resulted in a reduction of the mechanical loading in the lower leg muscles. We conclude that the use of unstable surfaces does not necessarily challenge reactive motor control nor increase muscle loading per se. Thus, the characteristics of the unstable surface and the dynamics of the target task must be considered when designing perturbation-based interventions.

A Versatile Aerial Manipulator Design and Realization of UAV Take-Off from a Rocking Unstable Surface

UAVs are one of the fastest types of robots that can be deployed in a remote environment. Unfortunately, they have a limited flight time and therefore may need to stop occasionally in an unknown, uncontrolled area. However, conventional UAVs require flat and stationary surfaces for a safe landing and take-off. Some studies on adaptive landing approach for UAVs can be found in the past, but adaptive take-off from non-flat surfaces has not been discussed for the most part, yet. In this work, we discuss the problems associated with a conventional UAV take-off from non-flat surfaces and provide a novel approach for UAV take-off from a sloped or rocking surface. We also discuss the design of a novel multitasking three-arm aerial manipulator system with parallel link mechanism and achieve the above-mentioned task. With experiments, we show that the system can provide stability for a UAV landing on a rocking surface that allows for a safe take-off.

RANS modelling of a single wind turbine wake in the unstable surface layer

Unstable atmospheric conditions are often observed during the daytime over land and for significant periods offshore, and are hence relevant for wake studies. A simple k-ε RANS turbulence model for simulation of wind turbine wakes in the unstable surface layer is presented, which is based on Monin-Obukhov similarity theory (MOST). The turbulence model parametrizes buoyant production of turbulent kinetic energy (TKE) without the use of an active temperature equation, and flow balance is ensured throughout the domain by modifications of the turbulence transport equations. Large eddy simulations and experimental data from the literature are used for validation of the model.

Differences of Thigh Muscle Activation During Various Squat Exercise on Stable and Unstable Surfaces

PURPOSE: The purpose of this study was to compare thigh muscle activities and muscle co-activation when performing squats, wall squats, and Spanish squats on stable and unstable ground.METHODS: Twenty-two healthy male subjects (age: 22.50±2.70 years, height: 178.72±6.04 cm, mass: 76.50±6.80 kg, body mass index: 24.00±2.10 kg/m2, and Godin activity questionnaire: 56.30±24.10) voluntarily participated in the study. All of the participants performed three different squat exercises on the floor and the BOSU ball with an electromyograph attached to each participant’s quadriceps (rectus femoris, RF; vastus lateralis, VL; and vastus medialis, VM) and hamstrings (biceps femoris, BF; semitendinosus, ST; and semimembranosus, SM). Repeated measures of analysis of variance were utilized to compare muscle activity during the three squats exercises by floor type.RESULTS: RF (p<.001, η2=.689), VL (p<.001, η2=.622), and VM (p=.002, η2=.375) showed significant differences between exercises. Spanish squats yielded greater BF activity than did wall squats (p=.018, η2=.269). ST yielded greater muscle activity with the BOSU ball than on the floor (p=.018, η2=.269). Finally, there was a significant ground exercise interaction effect on the co-activation, showing greater muscle co-activation with Spanish squats on the BOSU ball compared to squats, squats on the BOSU ball, and wall squat on the BOSU ball.CONCLUSIONS: The findings of this study indicate that Spanish squats could be an effective exercise option for the facilitation of RF, VL, VM, and BF muscle activation. In particular, performing Spanish squats on an unstable surface could be useful for patients who need to improve their quadriceps muscle activation.