Chiang Liu

Whole-body vibration combined with extra-load training for enhancing the strength and speed of track and field athletes.

Abstract Wang, H-H, Chen, W-H, Liu, C, Yang, W-W, Huang, M-Y, and Shiang, T-Y. Whole-body vibration combined with extra-load training for enhancing the strength and speed of track and field athletes. J Strength Cond Res 28(9): 2470–2477, 2014—The purpose of this study was to investigate whether whole-body vibration (WBV) combined with extra-load training can enhance the strength and speed of trained athletes compared with isolated WBV training or loaded training (LT) only. Twenty-one elite male track and field athletes were randomly assigned to a loaded vibration (LV) training group (n = 7), an unloaded vibration (ULV) training group (n = 7), and a LT group (n = 7). During 4 weeks of training, the LV group received the vibration stimulus (30 Hz and 4 mm) accompanied by a load comprising 75% of the maximum voluntary contraction (MVC), the ULV group received the same vibration stimulus without any load, and the LT group received only a load of 75% MVC without any vibration stimulus. The knee extensor isometric strength, and the concentric and eccentric strength were measured using an isokinetic dynamometer at 300°·s−1 at a 30-m sprint speed before and after the training period. A 2-way mixed analysis of variance (time × group) was used to analyze the differences. Significant time × group interactions were observed for all the dependent variables (p ⩽ 0.05). Regarding the post hoc analysis results, the LV group exhibited significant improvements for all the dependent variables after training (p ⩽ 0.05), whereas the ULV group exhibited significantly reduced sprint speeds (p ⩽ 0.05). The LV group demonstrated significantly superior eccentric strength compared with the ULV and LT groups after training (p ⩽ 0.05), and the LV group also produced significantly superior sprint speeds compared with the ULV group after training (p ⩽ 0.05). Vibration combined with extra-load training for 4 weeks significantly increased the muscle strength and speed of the elite male track and field athletes.

Chronic effects of whole-body vibration on jumping performance and body balance using different frequencies and amplitudes with identical acceleration load

UNLABELLED Previous studies on vibration training have all been based on protocols at different combinations of frequencies and amplitudes without controlling the loading intensity. OBJECTIVES This study investigated the effect of an 8-week vibration training program, under identical acceleration loads with various frequencies and amplitudes, on jumping performance, muscle activation and body balance. DESIGN Fifty young adults were randomly assigned to an high-frequency (32 Hz, 1mm, and 4 g), low-frequency (18 Hz, 3 mm, and 4 g), or a control group. The high-frequency and low-frequency groups underwent 60 s of squats exercise on the specific vibration platform three times a week, whereas the control group was trained without vibration. METHODS A force platform was used to measure the center of pressure of a static single leg stance, and the heights and impulse of two consecutive countermovement jumps before and after intervention. The activation of the rectus femoris and biceps femoris were also measured synchronously by surface electromyography. RESULTS The heights and impulse of both the first and second countermovement jumps were significantly increased and the area of center of pressure was significantly decreased after training in both the high-frequency and low-frequency groups (P<.05). Consequently, activation of the rectus femoris during the first countermovement jump was significantly lower than the pre-training value in the HF group but increased in the low-frequency group after training (P<.05). CONCLUSIONS An 8-week identical acceleration vibration training regimen with various frequencies and amplitudes can significantly improve jumping performance and body balance, but the specific neuromuscular adaptation is possibly induced by different training settings.

Change in Pitching Biomechanics in the Late-inning in Taiwanese High School Baseball Pitchers

Abstract Pei-Hsi Chou, P, Huang, Y-P, Gu, Y-H, Liu, C, Chen, S-K, Hsu, K-C, Wang, R-T, Huang, M-J, and Lin, H-T. Change in pitching biomechanics in the late-inning in Taiwanese high school baseball pitchers. J Strength Cond Res 29(6): 1500–1508, 2015—Repetitive overhead throwing may result in overuse injuries and a change in the pitching mechanics of a baseball pitcher. Accordingly, the purpose of this study is to quantify the changes in the muscle strength and pitching motion kinematics in the late-innings stage of a baseball game. Sixteen healthy baseball pitchers (16.77 ± 0.73 years) recruited from a high school, which won the National High School Baseball Championship in Taiwan in 2011; each performed 100 pitches in a bullpen throwing session. Isometric muscle strength measurements and joint kinematic data were obtained before and after the throwing session. The mean Borgs Rating of Perceived Exertion index was found to have a value of 14.14, indicating a medium-to-large degree of perceived tiredness. The results showed that the ball velocity and horizontal abduction angle decreased significantly as the pitchers became tired. Moreover, the upper torso forward tilt and knee flexion angle both increased significantly at the moment of ball release. Finally, the muscle strength of the upper extremity remained decreased 2 days after the bullpen throwing session. Overall, the results suggest that an adequate amount of rest and specific strengthening programs for the shoulder external rotator, shoulder internal rotator, shoulder flexor, shoulder extensor, shoulder adductor, and shoulder abductor muscles are recommended to the coaches and for adolescent baseball pitchers. In addition, the changes in pitching mechanics noted in this study should be carefully monitored during the course of a baseball game to minimize the risk for overuse injuries.

Effects of forefoot bending elasticity of running shoes on gait and running performance.

The aim of this study was to investigate the effects of forefoot bending elasticity of running shoes on kinetics and kinematics during walking and running. Twelve healthy male participants wore normal and elastic shoes while walking at 1.5m/s, jogging at 2.5m/s, and running at 3.5m/s. The elastic shoes were designed by modifying the stiffness of flexible shoes with elastic bands added to the forefoot part of the shoe sole. A Kistler force platform and Vicon system were used to collect kinetic and kinematic data during push-off. Electromyography was used to record the muscle activity of the medial gastrocnemius and medial tibialis anterior. A paired dependent t-test was used to compare the various shoes and the level of significance was set at α=.05. The range of motion of the ankle joint and the maximal anterior-posterior propulsive force differed significantly between elastic and flexible shoes in walking and jogging. The contact time and medial gastrocnemius muscle activation in the push-off phase were significantly lower for the elastic shoes compared with the flexible shoes in walking and jogging. The elastic forefoot region of shoes can alter movement characteristics in walking and jogging. However, for running, the elasticity used in this study was not strong enough to exert a similar effect.

Dual-frequency whole body vibration enhances vertical jumping and change-of-direction ability in rugby players

Background Traditional vertical and side-alternating whole body vibrations (WBV) can effectively improve muscle power performance but have a limited efficacy for enhancing change-of-direction (COD) ability. Novel dual-plate WBV uniquely providing various directions of movements with higher and distinctive frequencies for each leg may cause better acute effect on muscle power and stretch-shortening cycle efficacy contributing to COD ability. Therefore, the purpose of this study was to investigate the acute effect of dual- or single-frequency WBV on squat jumps (SJs), countermovement jumps (CMJs), eccentric utilization ratios (EURs), and COD ability in rugby players. Methods Fourteen male rugby players were recruited and performed a 4 min partial squat with 3 types of WBV protocols on a dual-plate WBV machine, including 1 dual-frequency WBV protocol (DFW) with the dominant leg receiving 35 Hz and the non-dominant leg receiving 45 Hz, and 2 single-frequency WBV protocols (SFWs) with 35 Hz or 45 Hz provided to both legs (SFW35Hz and SFW45Hz) on 3 different days. Results The results showed that all the vibration protocols significantly improved SJ and CMJ performances (SJ: p = 0.008; CMJ: p < 0.001), but did not significantly change EURs (p > 0.05). In addition, only the DFW significantly improved COD ability (p = 0.001 for the pre–post comparison). Conclusion A 4 min dual-frequency WBV session improved both vertical jumping and COD ability in rugby players, suggesting that this could be a potential warm-up protocol for athletes.

Effects of compression garments on surface EMG and physiological responses during and after distance running

Background The few previous studies that focused on the effects of compression garments (CG) on distance running performance have simultaneously measured electromyogram, physiological, and perceptual parameters. Therefore, this study investigated the effects of CG on muscle activation and median frequency during and after distance running, as well as blood-lactate concentration and rating of perceived exertion (RPE) during distance running. Methods Eight healthy male recreational runners were recruited to randomly perform two 40 min treadmill running trials, one with CG, and the other with control garment made of normal cloth. The RPE and the surface electromyography (EMG) of 5 lower extremity muscles including gluteus maximus (GM), rectus femoris (RF), semitendinosus (ST), tibialis anterior (TA), and gastrocnemius (GAS) were measured during the running trial. The blood-lactate levels before and after the running trial were measured. Results Wearing CG led to significant lower muscle activation (p  <  0.05) in the GM (decreased 7.40%–14.31%), RF (decreased 4.39%–4.76%), and ST (decreased 3.42%–7.20%) muscles; moreover, significant higher median frequency (p < 0.05) in the GM (increased 5.57%) and ST (increased 10.58%) muscles. Wearing CG did not alter the RPE values or the blood-lactate levels (p > 0.05). Conclusion Wearing CG was associated with significantly lower muscle activation and higher median frequency in the running-related key muscles during distance running. This finding suggested that wearing CG may improve muscle function, which might enhance running performance and prevent muscle fatigue.

Various performance-enhancing effects from the same intensity of whole-body vibration training

Purpose The purpose of this study was to compare the effects of an 8-week whole-body vibration training program in various frequency and amplitude settings under the same acceleration on the strength and power of the knee extensors. Methods Sixty-four young participants were randomly assigned to 1 of 4 groups with the same acceleration (4 g): high frequency and low amplitude (n = 16, 32 Hz, 1 mm) group, medium frequency and medium amplitude (n = 16, 18 Hz, 3 mm) group, low frequency and high amplitude (n = 16, 3 Hz, 114 mm) group, and control (n = 16, no vibration) group. All participants underwent 8 weeks of training with body mass dynamic squats, 3 sessions a week. Results The results showed that the high frequency and low amplitude group increased significantly in isometric contraction strength and 120°/s isokinetic concentric contraction strength; the medium frequency and medium amplitude group increased significantly in 60°/s and 120°/s isokinetic strength of both concentric and eccentric contraction; and the low frequency and high amplitude group increased significantly in 60°/s and 120°/s isokinetic eccentric contraction strength. Conclusion All frequency and amplitude settings in the 8-week whole-body vibration training increased muscle strength, but different settings resulted in various neuromuscular adaptations despite the same intensity.

Warm-up effects from concomitant use of vibration and static stretching after cycling.

BACKGROUND Static stretch is routinely used in traditional warm-up but impaired muscle performance. Combining vibration with static stretching as a feasible component may be an alternative to static stretching after submaximal aerobic exercise to improve jumping as well as flexibility. Therefore, the purpose of this study was to investigate and compare the effects of aerobic exercise, static stretching, and vibration with static stretching on flexibility and vertical jumping performance. METHODS A repeated measures experimental design was used in this study. Twelve participants randomly underwent 5 different warm-ups including cycling alone (C warm-up), static stretching alone (S warm-up), combining vibration with static stretching (VS warm-up), cycling followed by S (C+S warm-up), and cycling followed by VS (C+VS warm-up) on 5 separate days. Sit-and-reach, squat jump (SJ), and counter movement jump (CMJ) were measured for pre- and post- tests. RESULTS The sit-and-reach scores after the S, VS, C+S and C+VS warm-ups were significantly enhanced (P<0.001), and were significantly greater than that of the C warm-up (P<0.05). The jumping height of SJ and CMJ after the C and C+VS warm-ups were significantly increased (P<0.05), whereas a significant reduction was found after the S warm-up (P<0.05). CONCLUSIONS Vibration combined with stretching after submaximal cycling exercise (C+VS warm-up) could be a feasible warm-up protocol to improve both flexibility and vertical jump performance, compared with the traditional warm-up (C+S warm-up).