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In general, different training practice times may be associated with altered neuromuscular response in athletes during periods of acute fatigue and in response to post-effort recovery methods. The present investigation was purposed to analyze the electromyographic performance of knee extensor muscles after fatigue and cold-water immersion in university athletes with different practice times. Participants (n=24) were divided into two groups according to practical experience: G1 (6.60±0.70 years) and G2 (11.57±0.44 years); electromyography procedures were performed during an isometric knee extensor exercise. There were no differences in the comparisons between groups (p>0.05). Considering the moment of analysis, root mean square (RMS) measurements of the vastus lateralis and vastus medialis muscle were higher at the post-cryotherapy moment, when compared to the initial and post-exhaustion moments (p<0.001). No changes were observed in relation to muscle strength. In conclusion, neuromuscular performance of knee extensor muscles was not affected by the history of sports practice in university athletes. [ABSTRACT FROM AUTHOR]

Copyright of Revista Brasileira de Prescrição e Fisiologia do Exercício is the property of Instituto Brasileiro de Pesquisa e Ensino em Fisiologia do Exercicio and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of the present study was to analyze the electric activity of the vastus medialis (VM) and vastus lateralis (VL) in two differing angles (70° and 90° of knee flexion) during maximum voluntary contraction in squat exercise. Fifteen male subjects composed the sample of the study. As criteria they were untrained for more than 12 months (age of 28.0 ± 4.6 years, height of 180.0 ± 5.2 cm, weight of 80.0 ± 3.2 kg and body index mass of 24.2 ± 1.6 kg/m²). Subjects accomplished three maximum voluntary isometric contractions (MVIC) in squat exercise with 70° and 90° of knee flexion and separate at least in 72 h each. Data normalization occurred by average of values in RMS. Procedure adopted followed ISEK's recommendations. No significant differences (p > .05) were found between the angles VL 70° vs VM 70°, VL 90° vs VM 90°, VL 70° vs VL 90°, and VM 70° vs VM 90°. Results allowed for the conclusion that there seems to exist a balance in electric activity between VL and VM during MVIC with 70° and 90° of knee flexion in untrained subjects.

The aim of the present study was to analyze the electric activity of the vastus medialis (VM) and vastus lateralis (VL) in two differing angles (70° and 90° of knee flexion) during maximum voluntary contraction in squat exercise. Fifteen male subjects composed the sample of the study. As criteria they were untrained for more than 12 months (age of 28.0 ± 4.6 years, height of 180.0 ± 5.2 cm, weight of 80.0 ± 3.2 kg and body index mass of 24.2 ± 1.6 kg/m²). Subjects accomplished three maximum voluntary isometric contractions (MVIC) in squat exercise with 70° and 90° of knee flexion and separate at least in 72 h each. Data normalization occurred by average of values in RMS. Procedure adopted followed ISEK's recommendations. No significant differences (p > .05) were found between the angles VL 70° vs VM 70°, VL 90° vs VM 90°, VL 70° vs VL 90°, and VM 70° vs VM 90°. Results allowed for the conclusion that there seems to exist a balance in electric activity between VL and VM during MVIC with 70° and 90° of knee flexion in untrained subjects. [ABSTRACT FROM AUTHOR]

Objective: To investigate whether performing a low-intensity, single-joint exercises for knee extensors was an efficient strategy for increasing the number of motor units recruited in the vastus lateralis muscle during a subsequent multi-joint exercises. Methods: Nine healthy male participants (23.33±3.46 yrs) underwent bouts of exercise in which knee extension and 45°, and leg press exercises were performed in sequence. In the low-intensity bout (R30), 15 unilateral knee extensions were performed, followed by 15 repetitions of the leg presses at 30% and 60% of one maximum repetition load (1-MR), respectively. In the high-intensity bout (R60), the same sequence was performed, but the applied load was 60% of 1-MR for both exercises. A single set of 15 repetitions of the leg press at 60% of 1-MR was performed as a control exercise (CR). The surface electromyographic signals of the vastus lateralis muscle were recorded by means of a linear electrode array. The root mean square (RMS) values were determined for each repetition of the leg press, and linear regressions were calculated from these results. The slopes of the straight lines obtained were then normalized using the linear coefficients of the regression equations and compared using one-way ANOVAs for repeated measures. Results: The slopes observed in the CR were significantly lower than those in the R30 and R60 (p<0.05). Conclusions: The results indicated that the recruitment of motor units was more effective when a single-joint exercise preceded the multi-joint exercise. Article registered in the Australian New Zealand Clinical Trials Registry (ANZCTR) under the number ACTRN12609000413224. [ABSTRACT FROM AUTHOR]

Copyright of Revista Portuguesa de Ciências do Desporto is the property of Universidade do Porto, Faculdade de Desporto and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objective: The purpose of this study was to evaluate the amplitude and onset of electrical activation of the vastus medialis obliquus (VMO), vastus lateralis longus (VLL) and vastus lateralis obliquus (VLO) during functional activities in individuals with patellofemoral pain syndrome (PFPS). Methods: Twenty women participated in the study: ten in a control group and ten in the group with PFPS. The electromyographic signal of the quadriceps muscle was detected using simple active differential surface electrodes and a four-channel electromyography system, during open kinetic chain activities (using an isokinetic dynamometer) and closed kinetic chain activities (step and squat maneuvers). For the statistical analysis, Student's t test and ANOVA with Tukey's post-hoc method were used, with a significance level of p≤0.05. Results: The results suggested that the electrical activation of the VMO was less intense than in the VLO (p=0.04) and that there was greater delay in VMO onset (p=0.0023) in the group with PFPS, with regard to all of the functional activities evaluated. There was a significant difference between the VMO and VLO in relation to the activities of isokinetic extension at 30°/s (p=0.042) and step down with knee flexion at 75° (p=0.038) in the group with SDPF, and in the activities of rising from a bench (p=0.041), single-leg hop (p=0.046) and heel raising (p=0.004) in the control group. Conclusions: Under the experimental conditions used, this study suggests that there is an imbalance in the electric activity and abnormal recruitment patterns among the VMO, VLL and VLO muscles in individuals with PFPS, with greater delay and lower amplitude of activation of the VMO in this group. [ABSTRACT FROM AUTHOR]

The purpose of this study was to analyze the behavior of root mean square (RMS) and median frequency (MF) electromyographic variables from rectus femoris (RF), vastus medialis (VM) and vastus lateralis (VL) muscles of 10 volunteers during the execution time of isometric knee extension exercise performed with 20%, 30%, 40% and 50% of maximal voluntary contraction (MVC). A specific chair, load cell and digital display were used to perform the exercise. The electromyographic signals were obtained by surface electrodes, acquisition module of biological signals, A/D board, specific software calibrated with frequency rate: 1000Hz, gain: 1000 times, high pass filter: 20Hz and low pass filter: 500Hz. The RMS and MF values were calculate in each 5% of total exercise execution time in each load, and were normalized by MVC. The normalized values were analyzed between the initial time with others percentages of time and all values were correlated in relation to the total time. The results showed that the RMS obtained from VM and VL muscles presented the characteristic behavior of muscular fatigue by the increasing of RMS with time, which predominantly happen after 60% of total time. The MF decreases with total time only to RF muscle. With these behaviors, we concluded that the muscles analyzed here present different endurance capacity, which may accomplish rehabilitation and training programs. [ABSTRACT FROM AUTHOR]