Assessment of lower extremity bilateral asymmetries in soccer players is important for both injury prevention and performance. The purpose of this investigation was to compare isokinetic knee extensor assessment of asymmetry with a more specific countermovement jump (CMJ). Forty-six Brazilian male professional soccer players participated in this study. The maximal power, maximal force and impulse were determined during CMJ and the total work and peak torque at 60, 180, and 300°·s during isokinetic leg extension, separately for each leg. Factor analysis was performed for all investigated variables, and the diagnostic concordance between different criteria was analyzed by McNemar's χ test. The factor analysis showed that the isokinetic and CMJ tests were widely independent methods for the assessment of bilateral differences. Concordance of the diagnostic information could only be found between the maximal force during CMJ and the total work and peak torque at 180 and 300°·s during isokinetic leg extension. Impulse and maximal power during CMJ on a double force platform appear to be appropriate additional variables for the identification of bilateral differences. Therefore, it might be pertinent to perform, in addition to isokinetic assessment, a vertical jump test on a force platform to assure widespread and reliable diagnostic information.

Most studies about human responses to mechanical vibrations involve whole-body vibration and vibration applied perpendicularly to the tendon or muscle. The aim of the present study was to verify the effects of mechanical vibration applied in the opposite direction of muscle shortening on maximal isometric strength of the flexor muscles of the elbow due to neural factors. Conventional isometric training with maximal isometric contractions (MVCs) and isometric training with vibrations were compared. Nineteen untrained males, ages 24 +/- 3.28 years, were divided into 2 training groups. Group 1 performed conventional isometric training and group 2 isometric training with mechanical vibrations (frequency of 8 Hz and amplitude of 6 mm). Both groups executed 12 MVCs with a duration of 6 seconds and 2-minute intervals between the repetitions. The subjects trained 3 times per week for 4 weeks. The strength of the group subjected to vibrations increased significantly by 26 +/- 11% (p < 0.05), whereas the strength of the group with conventional isometric training increased only 10 +/- 5% (p < 0.05). These data suggest that training with vibrations applied in the opposite direction of muscle shortening enhances the mechanism of involuntary control of muscle activity and may improve strength in untrained males. Since these findings were in untrained males, further studies with athletes are necessary in order to generalize the results to athletes' training, although it seems that it would be possible.

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The aim of this study was to compare the chronic effects of different frequencies of mechanical vibrations, applied in the direction of the resultant muscle forces' vector addition, on the performance of the lower extremities. After performing the maximal voluntary contraction (MVC), squat jump (SJ), countermovement jump (CMJ), multiple vertical jumps and running speed tests, 55 male volunteers were distributed into 4 groups: an Isometric group, an 8-Hz group, a 26-Hz group and a Control group. After a 4-week training period, the same tests were performed. The training groups reached a significant increase of the MVC, but the increases of the 8-Hz (23.2%) and 26-Hz (22.2%) groups were higher than the Isometric group (12.1%). A significant increase was observed between SJ and CMJ values measured at the pre-test and the post-test stages in the 8-Hz (SJ=11.1%; CMJ=8.7%) and 26-Hz groups (SJ=9.6%; CMJ=7.5%). No differences were observed between 8-Hz and 26-Hz groups. The application of vibrations of 8 Hz and 26 Hz, directed to the resulting muscle forces, was able to increase the performance of the lower extremities. This kind of local vibration did not produce positive effects on multiple vertical jumps or running speed.

The purpose of this study was to assess the effect of training load regulation, using the CMJ at the beginning of the session, on the total plyometric training load and the vertical jump performance. 44 males were divided into 4 groups: No Regulation Group (nRG), Regulation Group (RG), Yoked Group (YG) and Control Group (CG). The nRG received 6 weeks of plyometric training, with no adjustment in training load. The RG underwent the same training; however, the training load was adjusted according to the CMJ performance at the beginning of each session. The adjustment made in RG was replicated for the volunteers from the corresponding quartile in the YG, with no consideration given to the YG participant's condition at the beginning of its session. At the end of the training, the CMJ and SJ performance of all of the participants was reassessed. The total training load was significantly lower (p=0.036; ES=0.82) in the RG and the YG (1905±37 jumps) compared to the nRG (1926±0 jumps). The enhancement in vertical jump performance was significant for the groups that underwent the training (p<0.001). Vertical jump performance, performed at the beginning of the session, as a tool to regulate the training load resulted in a decrease of the total training load, without decreasing the long-term effects on vertical jump performance.

The objective was to estimate the reliability and criterion-related validity of the Jump-and-Reach Test for the assessment of squat, countermovement, and drop jump performance of 32 male Brazilian professional volleyball players. Performance of squat, countermovement, and drop jumps with different dropping heights was assessed on the Jump-and-Reach Test and the measurement of flight time, then compared across different jump trials. The very high reliability coefficients of both assessment methods and the lower correlation coefficients between scores on the assessments indicate a very high consistency of each method but only moderate covariation, which means that they measure partly different items. As a consequence, the Jump-and-Reach Test has good ecological validity in situations when reaching height during the flight phase is critical for performance (e.g., basketball and volleyball) but only limited accuracy for the assessment of vertical impulse production with different jump techniques and conditions.

The purpose of this study was to investigate the chronic effects of dynamic strength training (ST) with local vibration on the maximum strength of elbow flexor muscles. Twenty healthy male untrained volunteers were divided randomly into the following two groups: the conventional training group (CTG) or the vibration training group (VTG). Both groups performed ST for 12 weeks, three times a week. The ST protocol included four sets of 8-10 repetition maximums (RMs) of unilateral elbow flexion exercise. The VTG performed this training protocol with local vibration at a frequency of 30 Hz and amplitude of 6 mm. The mean values of the one repetition maximum (1RM) tests for both groups increased significantly from the pretest week to the fourth week and from the fourth week to the eighth week (CTG: mean 19.02, s = 7.88%, p = 0.01; mean 10.50, s = 6.86%, p = 0.019, respectively; VTG: mean 16.02, s = 8.30%, p = 0.017; mean 12.55, s = 8.76%, p = 0.019, respectively). The increases in the maximal voluntary contraction (MVC) tests were also statistically significant from the pretest week to the fourth week and from the fourth week to the eighth week (CTG: mean 12.32, s = 8.33%, p = 0.004; mean 9.95, s = 5.32%, p = 0.006, respectively; VTG: mean 10.16, s = 11.71%, p = 0.003; mean 10.36, s = 2.96%, p = 0.01, respectively). There was no significant difference between the 1RM and MVC test results in the eighth and twelfth weeks in either group. No significant differences were observed between the groups (p < 0.05). In conclusion, the application of local vibration does not change the chronic effects of dynamic ST in untrained individuals.

The aim of this study was to verify the acute effects of the application of local vibration on upper limbs during resistance training on the number of maximum repetitions, metabolic and hormonal responses. 32 volunteers performed a maximum voluntary contraction test during a lat pulldown exercise. After the test, all volunteers underwent one conventional resistance training session and one resistance training session with local vibration. In both interventions, volunteers performed 4 sets with the highest possible number of repetitions of the lat pulldown exercise at 55% of maximum voluntary contraction. During the vibratory resistance training intervention, vibration was locally applied (20-Hz and 12-mm). During the conventional resistance training, volunteers performed the same procedures without vibration. Blood samples were taken at each experimental session before and 5 min after the end of each intervention. No significant differences were observed in number of maximum repetitions between the series of vibratory and conventional training. Serum testosterone, cortisol and lactate were significantly increased after 2 interventions. Vibratory resistance training induced greater increases in testosterone and lactate concentrations. No significant changes were found in creatine kinase, creatinine or urea concentration. These data indicate that local vibration increases the metabolic and anabolic response to the resistance training, without changing the training volume.