Glauber Ribeiro Pereira

INFLUENCE of HIP EXTERNAL ROTATION on HIP ADDUCTOR and RECTUS FEMORIS MYOELECTRIC ACTIVITY DURING A DYNAMIC PARALLEL SQUAT

Pereira, GR, Leporace, G, Chagas, DV, Furtado, LFL, Praxedes, J, and Batista, LA. Influence of hip external rotation on hip adductor and rectus femoris myoelectric activity during a dynamic parallel squat. J Strength Cond Res 24(10): 2749-2754, 2010-This study sought to compare the myoelectric activity of the hip adductors (HAs) and rectus femoris (RF) when the hip was in a neutral position or externally rotated by 30° or 50° (H0, H30, and H50, respectively) during a parallel squat. Ten healthy subjects performed 10 repetitions of squats in each of the 3 hip positions and the myoelectric activities of the HAs and RF were recorded. The signal was then divided into categories representing concentric (C) and eccentric (E) contractions in the following ranges of motion: 0-30° (C1 and E1), 30-60° (C2 and E2), and 60-90° (C3 and E3) of knee flexion. From those signals, an root mean square (RMS) value for each range of motion in each hip position was obtained. All values were normalized to those obtained during maximum voluntary isometric contraction. We found that HAs showed a significant increase in myoelectric activity during C3 and E3 in the H30 and H50 positions, as compared with H0. Meanwhile, RF activity did not significantly differ between hip positions. Both muscles showed higher activation during 60-90° (C3 and E3) of knee flexion, as compared with 0-30° (C1 and E1) and 30-60° (C2 and E2). The results suggest that if the aim is to increase HA activity despite the low percentage of muscle activation, squats should be performed with 30° of external rotation and at least 90° of knee flexion.

Isometric fatigue patterns in time and time–frequency domains of triceps surae muscle in different knee positions

The occurrence of fatigue in triceps surae (TS) muscles during sustained plantar flexion contraction is investigated by means of the RMS electromyogram (EMG) and the instantaneous median frequency (IMF) of the short time Fourier transform (STFT). Six male subjects realized a 40% maximal plantar flexion isometric voluntary contraction until fatigue in two knee positions. Electrodes were positioned on gastrocnemius medialis, gastrocnemius lateralis and soleus muscles. The torque (TO) and EMG signals were synchronized. The RMS and the median of the IMF values were obtained, respectively, for each 250 ms and 1s windows of signal. Each signal was segmented into 10 epochs, from which the mean values of IMF, RMS and TO were obtained and submitted to linear regressions to determine parameter trends. Friedman test with the Dunns post hoc were used to test for differences among muscles activation for each knee position and among slopes of regression curves, as well as to observe changes in TS RMS values over time. The results indicate different activation strategies with the knee extended (KE) in contrast to knee flexed (KF). With the KE, the gastrocnemii showed typical fatigue behavior with significant (p<0.05) IMF reductions and RMS increases over time, while soleus showed concomitant RMS and IMF increases (p<0.05) suggesting an increased soleus contribution to the torque production. With KF, the gastrocnemii were under activated, increasing the role of soleus. Thus, time-frequency analysis represented an important tool for TS muscular fatigue evaluation, allowing differentiates the role of soleus muscle.

Reducing cross terms effects in the Choi-Williams transform of mioelectric signals

This study aims at investigating the effect of removing the negative values of Choi-Wiliams distribution (CWD) related to the electromyogram (EMG) for visualization and instantaneous median frequency (IMF) estimation. Beyond the EMG signals from triceps surae and biceps brachialis, the CWD was applied in a simulated sinusoidal signal as like in stationary and non-stationary simulated EMG signals (SES). The CWD negative values of all simulated and EMG signals were removed. The IMF values were obtained for SES and EMG. The CWD IMF values from SES and EMG were thus compared with the IMF values from short time Fourier transform (STFT) by means of correlation. The suppression of negative values from the CWD reduced cross terms influence and improved visualization, as shown by the increased correlation coefficient between the IMF values. Before this suppression, the extracted IMF values showed large oscillation along the time, with various spurious values beyond 500Hz, which disappeared after the suppression. Moreover, this procedure seems to be especially useful for non-stationary signals.

Differences in time-frequency representation of lower limbs myoelectric activity during single and double leg landing in male athletes

This study compared the instantaneous median frequency (IMF) obtained by means of a Choi-Williams transform of an electromyogram of the lower-limb muscles during single-leg (SL) and double-leg (DL) landings performed by fifteen male athletes. The IMF values of the rectus femoris (RF), biceps femoris (BF) and hip adductors (HA) were compared between two landing tasks, within each landing, and before and after ground contact (GC). The IMF values of the RF did not change between landings in contrast to those of the BF, which presented from 20- to 40-ms higher SL values before GC and from 40 to 60 ms after GC. HA presented higher SL values during the 40-60 ms range before GC. Within each landing, the RF IMF decreased from 40 ms to 60 ms after GC in the SL. Similar results were found for the HA IMF, which decreased from 40ms to 80 ms after GC. The BF IMF showed no significant change. These results suggest muscle recruitment related to anterior cruciate ligament protection since the IMF values of the RF decreased in the SL, whereas the BF IMF increased. Results for the HA showed the importance of hip muscles in stabilizing the core region, allowing the activation of distal muscles with greater safety.

Comparison of quadriceps and hamstrings activation ratio between healthy and anterior cruciate ligament reconstructed subjects

The aim of this study was to compare the ratio of activation of the vastus lateralis (VL) and biceps femoris (BF) muscles between healthy (CG) and anterior cruciate ligament reconstructed (ACL-R) subjects during gait. Nineteen subjects, ten from GC and nine from ACL-R, participated in the study. VL and BF activity was captured and the VL/BF ratio was obtained by dividing each point on the curve of the vastus lateralis and biceps femoris. This ratio was compared between the two groups using an unpaired t test (a = 0.05). Differences between the two groups were found (p <;0.05) in the initial double limb stance phase, representing the initial 10% of the gait cycle. There were no differences for the other gait phases (p <;0.05). It is concluded that the differences in ratio between knee extensors and flexors persist even one year after ACL reconstructions. These differences may be related to protective strategies to avoid excessive stress caused by the anterior shear of the tibia over the femur as a function of excessive vastus lateralis contraction. However, it is unknown whether this strategy has any relation to the risk of developing knee osteoarthritis in the future.

Ativação muscular do quadril e do joelho em duas aterrissagens realizadas por atletas do sexo masculino

OBJECTIVE: To compare the myoelectric activity before and after ground contact between single leg (SL) and double leg (DL) landings in male athletes. PARTICIPANTS: Fifteen male volleyball athletes without signs and symptoms of lesions in the lower extremities, with a minimum of three years experience in the sport (13 ± 1 years, 1.70 ± 0.12 m, 60 ± 12 kg). MEASUREMENTS: Participants performed two vertical jumps, landing unilaterally and bilaterally. The myoelectric activity of the rectus femoris (RF), biceps femoris (BF), hip adductors (HA) and the BF/RF ratio were compared between the two landings and between the phases characterized by 100ms before (PRE) and after 100 ms (POST) ground contact using ANOVA two-way test with post hoc test of Bonferroni (α = 5%). RESULTS: In both landings activation of RF was higher in the POST in relation to the PRE (p <0.0001). Comparing the landings in the same phase statistical differences (p = 0.2212) were not found. Although the BF did not present significant differences between the PRE and POST in each landing (p = 0.2321), its activation was higher in SL (p = 0.0051). The HA showed greater activation in the POST during the SL (p = 0.0013), however there were no differences when comparing the two landings (p = 0.9233). The BF/RF ratio was higher in both landings during PRE (p = 0.0012). Nevertheless, no differences between the landings (p = 0.7037) were found. CONCLUSION: The results suggest that each muscle has a different role during landing tasks in men. While RF has the main function to decelerate the knee and the downward movement, characterized by increased activation in the POST, BF seems to attenuate the loads on the knee in activities of higher impact, staying more active throughout the cycle in the SL. The increased activation of HA after ground contact in the SL highlights the importance of core region in stabilizing the pelvis in situations of great instability. Further studies are needed to determine the effects of muscle activation at the imposition of mechanical load on the knee that are potentially harmful to male athletes.

Especificidade da atividade mioelétrica no agachamento excêntrico declinado em 25º e no agachamento padrão com diferentes sobrecargas

OBJETIVO: O objetivo neste estudo foi comparar a atividade mioeletrica entre o agachamento unilateral declinado e o agachamento unilateral em superficie plana, no deslocamento vertical de duas diferentes quantidades de massa. PARTICIPANTES: Um grupo de oito sujeitos treinados recreacionalmente sem sinais e sintomas de lesoes nas extremidades inferiores. PROCEDIMENTOS: Em dias separados, os sujeitos realizaram dois tipos distintos de agachamento unilateral na fase descendente, diferenciados em funcao da direcao da base de sustentacao, sendo uma horizontal e outra inclinada a 25°. Os dois tipos de agachamento foram realizados com dois valores de carga, com o peso do proprio corpo e com sobrecarga representativa de 15 repeticoes maximas (15RM). MENSURACOES: As atividades mioeletricas do reto femoral, vasto lateral, posteriores de coxa mediais (semimembranoso e semitendinoso) e gastrocnemio medial foram mensuradas nas quatro situacoes de teste. RESULTADOS: O grupamento muscular quadriceps mostrou-se sensivel a magnitude do ângulo de inclinacao da plataforma, manifestando maior atividade no agachamento declinado, e nao apresentou aumentos na ativacao muscular como resposta ao aumento da carga. Os musculos mediais posteriores da coxa e o gastrocnemio medial nao se mostraram sensiveis a angulacao da plataforma nem ao aumento da sobrecarga. Apesar das taxas de co-contracao nao serem semelhantes entre as quatro situacoes testadas, as diferencas entre elas nao se mostraram estatisticamente significativas. CONCLUSAO: Os resultados confirmaram a maior ativacao do quadriceps gerada no agachamento declinado em comparacao ao agachamento realizado em superficie plana, sugerindo que esse exercicio pode constituir uma alternativa para programas de reabilitacao da tendinopatia patelar. Apesar de nao termos encontrado diferencas estatisticamente significativas em relacao a co-contracao muscular, os achados sugerem que esse exercicio deve ser utilizado com cautela, ja que o sinergismo muscular entre os musculos testados mostrou-se alterado em decorrencia de modificacoes no status direcional da superficie de apoio, o que pode comprometer a especificidade da exercitacao em relacao a atividades especificas, como as esportivas, nomeadamente quanto ao aspecto coordenacao.

In silico analysis and molecular dynamics simulation of human superoxide dismutase 3 (SOD3) genetic variants: PEREIRA et al.

Oxidative stress is a major factor in aging processes. Superoxide dismutase 3 (SOD3) plays a key role in the protection of extracellular oxidative stress. Missense mutations in SOD3 have been described to be associated with the occurrence of pulmonary, cardiovascular, and neoplastic diseases. This study aims to analyze the effects of missense mutations on the SOD3 structure and function by modeling a complete SOD3 structure as well as analyzing the differences between the wild‐types and mutants using computational simulations. Here, ten algorithms were used to predict the structural and functional effects of missense mutations. A complete model of SOD3 protein was made by ab initio and comparative modeling using the Rosetta algorithm and validated by PROCHECK, Verify 3D, QMEAN, and ProSa. Molecular dynamics (MD) simulations were performed and analyzed using the GROMACS package. The deleterious potential of the A58T and R231G mutants was not predicted by the majority of the used algorithms. The analyzed mutations were predicted as destabilizing by at least one algorithm. The MD analyses indicated that protein flexibility may be increased by all of the analyzed mutations, while the protein‐ligand stability may be decreased. They also suggested that the variants A91T and R231G increase the overall dimensions of SOD3 and decrease its accessible surface area. Our findings, therefore, indicated that the analyzed mutations could affect the protein structure and its ability to interact with other molecules, which may be related to the functional impairment of SOD3 upon A58T and R231G mutations, as well as their involvement in pathologies.

USE OF SPATIOTEMPORAL GAIT PARAMETERS TO DETERMINE RETURN TO SPORTS AFTER ACL RECONSTRUCTION

Objective : To compare gait spatiotemporal parameters of healthy and ACL reconstructed subjects in order to classify the status of gait normality. Methods : Fourteen healthy subjects and eight patients submitted to ACL reconstruction walked along a walkway while the lower limbs movement was captured by an infrared camera system. The frames where the initial contact and toe-off took place were determined and the following dependent variables, which were compared between groups through the Mann-Whitney test (a=0.05) were calculated: percentage of time in initial double stance, percentage of time in single stance, percentage of time in terminal double stance, stride length and gait velocity. Initially, all variables were compared between groups using a Mann-Whitney test. A logistic regression was applied, including all dependent variables, to create a model that could differentiate healthy and ACL reconstructed subjects. Results : ACL reconstructed group showed no differences in any spatiotemporal parameter of gait (p > 0.05) in relation to the control group, although the angular kinematic differences of the knee remained altered, as evidenced in a study with a similar sample. Conclusion : The regression classified all subjects as healthy, including the ACL reconstructed group, suggesting the spatiotemporal variables should not be used as the sole criterion of return to sports activities at the same level as prior to injury. Level of Evidence III, Case Control Study.

KNEE SYNERGISM DURING GAIT REMAIN ALTERED ONE YEAR AFTER ACL RECONSTRUCTION

ABSTRACT Objective: To compare the activation of the vastus lateralis (VL) and biceps femoris (BF) muscles during gait, as well VL/BF muscular co-contraction (MCC) between healthy (CG) and anterior cruciate ligament reconstructed (ACL-R) subjects. Methods: Nineteen subjects, ten controls and nine ACL-R patients had a VL and BF electromyogram (EMG) captured to calculate the MCC ratio. A Principal Component (PC) Analysis was applied to reduce the dimensionality effect of each of the MCC, VL and BF curves for both healthy and ACL reconstructed groups. The PC scores were used to calculate the standard distance (SD). SD values were employed in order to compare each dependent variable (MCC, VL and BF) between the two groups using unpaired t-test. Results: ACL-R group presented a lower VL activation at the beginning and at the end of the gait cycle, as compared to the control group. However, no difference was found for BF or VL/BF MCC. Conclusion: The gait analysis of ACL reconstructed patients demonstrated a persistent deficit in VL activation when compared to the control group, even one year after surgery. Level of Evidence III. Case Control Study