Are change of direction speed and agility different abilities from time and coordinative perspectives?

This study aimed to test whether agility and change of direction speed (COD) are independent capacities using the same movement pattern (1) in terms of the completion time and (2) the entropy. Seventeen semi-professional female football players participated in the study. The agility task consisted of a Y-shaped (45° COD) task with three possible exit options (center, right and left) performed pre-planned or in reaction to the movement of two testers (i.e., blocking exit gates). Players' acceleration was measured using an inertial measurement unit. Entropy was calculated from the acceleration signal and completion time was extracted using a magnet-based timing system. Significantly greater times and lower entropy (p<0.001) were found during agility runs to pre-planned COD runs. Furthermore, weak to moderate correlations were found between COD and agility for both completion time (r = 0.29, p<0.001) and entropy (r = 0.53, p<0.001, r2 = 28.1%). These results highlight that COD speed and agility are independent capacities and skills, and as such, should be tested and trained as distinct, separate qualities. Modifying task constraints including a reactive stimulus (i.e., cognitive factors), is essential for increasing task complexity by altering the biomechanical and coordinative aspects of the action.

Decision making influences movement variability and performance of high-level female football players in an elastic resistance task.

Introduction: The inclusion of sport-specific constraints in resistance training promotes the development of player abilities in an integrated way, which maximises the effectiveness of player adaptations induced by training. Considering that perceptual-cognitive abilities play a fundamental role in football, decision making could be introduced to enhance the cognitive similarity of resistance tasks to sport actions. However, it is unknown how decision making as a constraint could affect the player during an elastic resistance task. Therefore, the aim of this study was to investigate the effects of decision making of high-level female football players on movement variability and performance during an elastic band resistance task. Methods: Twenty-three high-level female football players performed the elastic resistance task with a ball, both as attackers and as defenders without decision making (NDM) and with decision making (DM). The movement variability was quantified using the sample entropy derived from the acceleration recorded with an accelerometer placed at the lower back of each player. The passing accuracy of the attacker was quantified using a scoring scale. Results: Results revealed that adding decision making to an elastic resistance task increased the movement variability of the defender but did not affect the movement variability of the attacker. In contrast, the passing accuracy of the attacker was reduced. Overall, the attacker had a higher movement variability compared to the defender. Discussion: These findings suggest that decision making, as a football-specific constraint, can enhance the potential of an elastic resistance task in training. This is due to the fact that it reduces control and regularity of movement for the defensive role player and increases technical difficulty for the attacking role player. Furthermore, these effects are beneficial, as they can promote the adaptive processes necessary to optimise the performance of the players.

Adding mechanical vibration to a half squat with different ballasts and rhythms increases movement variability.

The aim of this study was to determine whether whole body vibration increases movement variability while performing a half squat with different ballasts and rhythms through entropy. A total of 12 male athletes (age: 21.24 ± 2.35 years, height: 176.83 ± 5.80 cm, body mass: 70.63 ± 8.58 kg) performed a half squat with weighted vest, dumbbells and bar with weights suspended with elastic bands, with and without vibration at the squat rhythm of 40 and 60 bpm. Each ballast corresponded to 15% of the body mass. The movement variability was analysed by calculating the sample entropy of the acceleration signal, recorded at the waist using an accelerometer. With vibration, differences were found between weighted vest and dumbbells (t(121) = -8.81, p < 0.001 at 40 bpm; t(121) = -8.18, p < 0.001 at 60 bpm) and between weighted vest and bar at both rhythms (t(121) = -8.96, p < 0.001 at 40 bpm; t(121) = -8.83, p < 0.001 at 60 bpm). Furthermore, a higher sample entropy was obtained at 40 bpm with all ballasts (t(121) = 5.65, p < 0.001 with weighted vest; t(121) = 6.27, p < 0.001 with dumbbells; t(121) = 5.78, p < 0.001 with bar). No differences were found without vibration. These findings reveal that adding mechanical vibration to a half squat produces a non-proportional increase in movement variability, being larger when the ballast is placed on the upper limbs and when performed at a slow rhythm.

Influence of Turn Cycle Structure on Performance of Elite Alpine Skiers Assessed through an IMU in Different Slalom Course Settings.

Small differences in turn cycle structure, invisible to the naked eye, could be decisive in improving descent performance. The aim of this study was to assess the influence of turn cycle structure on the performance of elite alpine skiers using an inertial measurement unit (IMU) in different slalom (SL) course settings. Four SL courses were set: a flat-turned (FT), a steep-turned (ST), a flat-straighter (FS) and a steep-straighter (SS). Five elite alpine skiers (21.2 ± 3.3 years, 180.2 ± 5.6 cm, 72.8 ± 6.6 kg) completed several runs at maximum speed for each SL course. A total of 77 runs were obtained. Fast total times correlate with a longer initiation (INI) time in FT, a shorter steering time out of the turn (STEOUT) in the FT and FS and a shorter total steering time (STEIN+OUT) in the FT and SS courses. The linear mixed model used for the analysis revealed that in the FT-course for each second increase in the INI time, the total time is reduced by 0.45 s, and for every one-second increase in the STEOUT and STEIN+OUT times, the total time increases by 0.48 s and 0.31 s, respectively. Thus, to enhance descent performance, the skier should lengthen the INI time and shorten the STEOUT and STEIN+OUT time. Future studies could use an IMU to detect turn phases and analyze them using the other built-in sensors.

Validity of a Magnet-Based Timing System Using the Magnetometer Built into an IMU.

Inertial measurement units (IMUs) represent a technology that is booming in sports right now. The aim of this study was to evaluate the validity of a new application on the use of these wearable sensors, specifically to evaluate a magnet-based timing system (M-BTS) for timing short-duration sports actions using the magnetometer built into an IMU in different sporting contexts. Forty-eight athletes (22.7 ± 3.3 years, 72.2 ± 10.3 kg, 176.9 ± 8.5 cm) and eight skiers (17.4 ± 0.8 years, 176.4 ± 4.9 cm, 67.7 ± 2.0 kg) performed a 60-m linear sprint running test and a ski slalom, respectively. The M-BTS consisted of placing several magnets along the course in both contexts. The magnetometer built into the IMU detected the peak-shaped magnetic field when passing near the magnets at a certain speed. The time between peaks was calculated. The system was validated with photocells. The 95% error intervals for the total times were less than 0.077 s for the running test and 0.050 s for the ski slalom. With the M-BTS, future studies could select and cut the signals belonging to the other sensors that are integrated in the IMU, such as the accelerometer and the gyroscope.

Effect of vibration frequency on agonist and antagonist arm muscle activity.

PURPOSE: This study aimed to assess the effect of vibration frequency (f out) on the electromyographic (EMG) activity of the biceps brachii (BB) and triceps brachii (TB) muscles when acting as agonist and antagonist during static exercises with different loads. METHODS: Fourteen healthy men were asked to hold a vibratory bar as steadily as possible for 10 s during lying row (pulling) and bench press (pushing) exercise at f out of 0 (non-vibration condition), 18, 31 and 42 Hz with loads of 20, 50, and 80 % of the maximum sustainable load (MSL). The root mean square of the EMG activity (EMGRMS) of the BB and TB muscles was expressed as a function of the maximal EMGRMS for respective muscles to characterize agonist activation and antagonist coactivation. RESULTS: We found that (1) agonist activation was greater during vibration (42 Hz) compared to non-vibration exercise for the TB but not for the BB muscle (p < 0.05); (2) antagonist activation was greater during vibration compared to non-vibration exercise for both BB (p < 0.01) and TB (p < 0.05) muscles; (3) the vibration-induced increase in antagonist coactivation was proportional to vibration f out in the range 18-42 Hz and (4) the vibration-induced increase in TB agonist activation and antagonist coactivation occurred at all loading conditions in the range 20-80 % MSL. CONCLUSION: The use of high vibration frequencies within the range of 18-42 Hz can maximize TB agonist activation and antagonist activation of both BB and TB muscles during upper limb vibration exercise.

Efecto de 8 semanas de entrenamiento con vibraciones en la tercera edad / Effect of an 8-week vibration training program in the elderly

Introducción. La actividad física ha demostrado ser beneficiosa para mantener o mejorar la autonomía en la tercera edad, de la misma forma que el ejercicio con vibración (EJVb) en personas adultas ha demostrado generar rápidos beneficios. En el presente estudio se analizan los efectos de un programa de 8 semanas de EJVb de volumen reducido en la autonomía y la fuerza en un grupo de personas de la tercera edad. Material y métodos. Veintitrés participantes (18 mujeres y 5 varones, de edad comprendida entre 70 y 92 años, con una media de edad de 81,2 años), realizaron un entrenamiento de 5 series de 30s con vibraciones mecánicas a 25Hz y 2mm de amplitud 3 veces a la semana durante 8 semanas. Se valoró la fuerza isométrica de los músculos extensores de rodilla mediante una galga del MuscleLab® y la autonomía mediante la prueba Expanded-Timed-Get-Up-and-Go (ETGUG), ambos antes, después de las 8 semanas de entrenamiento y 8 semanas después de haber cesado el entrenamiento. Resultados. Se detectaron diferencias significativas entre los 3 momentos de intervención en la fuerza, en el tiempo total en completar el ETGUG y en los diferentes parciales del mismo con excepción del tiempo parcial de levantarse y realización del giro. El EJVb mejoró significativamente el tiempo en completar el ETGUG y la fuerza tras 8 semanas de entrenamiento. Sin embargo, estos beneficios solo perduraron en la velocidad de la marcha, pero no en la fuerza. Discusión. Los resultados de la prueba ETGUG denotaron cambios significativos en su totalidad, sin embargo, analizando sus diferentes partes, encontramos 2 parciales (levantarse y giro) en los que las diferencias no fueron significativas, probablemente a que los resultados no dependen exclusivamente de la capacidad física del participante, sino que están también relacionados con la habilidad coordinativa. Conclusiones. Ocho semanas de EJVb de volumen reducido en personas de la tercera edad mejoraron la autonomía, pero no la fuerza isométrica(AU)

Introduction. Physical activity has been shown to maintain or improve autonomy in the elderly. It has also been demonstrated that vibration exercise in adults achieves rapid benefits. This study analyses the effects of an 8-week program of reduced volume vibration training on autonomy and strength in a group of elderly subjects. Material and methods. The 23 participants (18 women and 5 men, aged between 70 and 92 years, mean age 81.2 years) underwent a training program of five 30-second series of mechanical vibrations at 25Hz and 2mm wavelength three times a week for eight weeks. The isometric strength of the extensor muscles of the knee was assessed with a MuscleLab® gauge, and autonomy was tested with the “Expanded-Timed-Get-Up-and-Go” (ETGUG) test, both before and immediately after the eight weeks of the program and then eight weeks afterwards. Results. Significant differences were detected between the three time points in strength, and also in total time taken to complete the ETGUG and the various sections of the test, with the exception of the time taken to stand up and to turn. The vibration training program significantly improved the time taken to complete the ETGUG and strength after eight weeks of training. However, these benefits only endured for walking speed, not for strength. Discussion. The results of the ETGUG test revealed significant changes overall. However, in two sections (standing up and turning) the differences were not significant, probably because the results do not depend exclusively on participants’ physical capacity but are also related to their coordination skills. Conclusions. Eight weeks of reduced volume vibration training in the elderly improved autonomy, but not isometric strength(AU)

[Effect of an 8-week vibration training program in the elderly]. / Efecto de 8 semanas de entrenamiento con vibraciones en la tercera edad.

INTRODUCTION: Physical activity has been shown to maintain or improve autonomy in the elderly. It has also been demonstrated that vibration exercise in adults achieves rapid benefits. This study analyses the effects of an 8-week program of reduced volume vibration training on autonomy and strength in a group of elderly subjects. MATERIAL AND METHODS: The 23 participants (18 women and 5 men, aged between 70 and 92 years, mean age 81.2 years) underwent a training program of five 30-second series of mechanical vibrations at 25 Hz and 2 mm wavelength three times a week for eight weeks. The isometric strength of the extensor muscles of the knee was assessed with a MuscleLab(®) gauge, and autonomy was tested with the "Expanded-Timed-Get-Up-and-Go" (ETGUG) test, both before and immediately after the eight weeks of the program and then eight weeks afterwards. RESULTS: Significant differences were detected between the three time points in strength, and also in total time taken to complete the ETGUG and the various sections of the test, with the exception of the time taken to stand up and to turn. The vibration training program significantly improved the time taken to complete the ETGUG and strength after eight weeks of training. However, these benefits only endured for walking speed, not for strength. DISCUSSION: The results of the ETGUG test revealed significant changes overall. However, in two sections (standing up and turning) the differences were not significant, probably because the results do not depend exclusively on participants' physical capacity but are also related to their coordination skills. CONCLUSIONS: Eight weeks of reduced volume vibration training in the elderly improved autonomy, but not isometric strength.