Júlio Cerca Serrão

NEUROMUSCULAR ACTIVITY DURING BENCH PRESS EXERCISE PERFORMED WITH AND WITHOUT THE PREEXHAUSTION METHOD

Brennecke, A, Guimarães, TM, Leone, R, Cadarci, M, Mochizuki, L, Simão, R, Amadio, AC, and Serrão, J. Neuromuscular activity during bench press exercise performed with and without the preexhaustion method. J Strength Cond Res 23(7): 1933-1940, 2009-The purpose of the present study was to investigate the effects of exercise order on the tonic and phasic characteristics of upper-body muscle activity during bench press exercise in trained subjects. The preexhaustion method involves working a muscle or a muscle group combining a single-joint exercise immediately followed by a multi-joint exercise (e.g., flying exercise followed by bench press exercise). Twelve subjects performed 1 set of bench press exercises with and without the preexhaustion method following 2 protocols (P1-flying before bench press; P2-bench press). Both exercises were performed at a load of 10 repetition maximum (10RM). Electromyography (EMG) sampled at 1 kHz was recorded from the pectoralis major (PM), anterior deltoid (DA), and triceps brachii (TB). Kinematic data (60 Hz) were synchronized to define upward and downward phases of exercise. No significant (p > 0.05) changes were seen in tonic control of PM and DA muscles between P1 and P2. However, TB tonic aspect of neurophysiologic behavior of motor units was significantly higher (p < 0.05) during P1. Moreover, phasic control of PM, DA, and TB muscles were not affected (p > 0.05). The kinematic pattern of movement changed as a result of muscular weakness in P1. Angular velocity of the right shoulder performed during the upward phase of the bench press exercise was significantly slower (p < 0.05) during P1. Our results suggest that the strategies set by the central nervous system to provide the performance required by the exercise are held constant throughout the exercise, but the tonic aspects of the central drive are increased so as to adapt to the progressive occurrence of the neuromuscular fatigue. Changes in tonic control as a result of the muscular weakness and fatigue can cause changes in movement techniques. These changes may be related to limited ability to control mechanical loads and mechanical energy transmission to joints and passive structures.

Biomechanical parameters of gait among transtibial amputees: a review

Rehabilitation for lower-limb amputees needs to focus on restoration of daily functions and independent locomotion. As gait is reestablished, reorganization of the motor pattern takes place in order to optimize the functions of the locomotor system. Biomechanics is a field of study that enables understanding of this reorganization. From such knowledge, appropriate strategies for recovering the autonomy of the means of locomotion can be established. Thus, this paper had the aim of reviewing the current status of the biomechanics of locomotion among unilateral transtibial amputees. To achieve this aim, papers written in English or Portuguese and published up to 2005 were selected from the Cochrane Library, PubMed, Scientific Electronic Library Online (SciELO), Literatura Latino-Americana e do Caribe em Ciências da Saúde (Lilacs) and Dedalus databases. In cases of transtibial amputation, the absence of plantar flexors negatively affects locomotion. Increased absorption and energy generation by the muscles that control the hip joint of the amputated leg can be considered to be the main compensatory strategy developed by unilateral transtibial amputees during gait. Factors associated with the characteristics of the amputation, prosthesis and experimental protocol used directly influence the results.

Contextualização da biomecânica para a investigação do movimento: fundamentos, métodos e aplicações para análise da técnica esportiva

Contextualizacao da biomecânica para a investigacao do movimento: fundamentos, metodos e aplicacoes para analise da tecnica esportiva

The countermovement jump to monitor neuromuscular status: A meta-analysis

OBJECTIVES The primary objective of this meta-analysis was to compare countermovement jump (CMJ) performance in studies that reported the highest value as opposed to average value for the purposes of monitoring neuromuscular status (i.e., fatigue and supercompensation). The secondary aim was to determine the sensitivity of the dependent variables. DESIGN Systematic review with meta-analysis. METHODS The meta-analysis was conducted on the highest or average of a number of CMJ variables. Multiple literature searches were undertaken in Pubmed, Scopus, and Web of Science to identify articles utilizing CMJ to monitor training status. Effect sizes (ES) with 95% confidence interval (95% CI) were calculated using the mean and standard deviation of the pre- and post-testing data. The coefficient of variation (CV) with 95% CI was also calculated to assess the level of instability of each variable. Heterogeneity was assessed using a random-effects model. RESULTS 151 articles were included providing a total of 531 ESs for the meta-analyses; 85.4% of articles used highest CMJ height, 13.2% used average and 1.3% used both when reporting changes in CMJ performance. Based on the meta-analysis, average CMJ height was more sensitive than highest CMJ height in detecting CMJ fatigue and supercompensation. Furthermore, other CMJ variables such as peak power, mean power, peak velocity, peak force, mean impulse, and power were sensitive in tracking the supercompensation effects of training. CONCLUSIONS The average CMJ height was more sensitive than highest CMJ height in monitoring neuromuscular status; however, further investigation is needed to determine the sensitivity of other CMJ performance variables.

Effects of creatine supplementation on strength and muscle hypertrophy: current concepts

A suplementacao de creatina vem sendo utilizada amplamente na tentativa de aumentar forca e massa magra em sujeitos saudaveis e atletas. Alem disso, diversos estudos tem sido conduzidos no intuito de desvendar os mecanismos responsaveis pelas eventuais adaptacoes a esse suplemento. Diante disso, essa revisao teve como objetivos: 1) discutir os principais estudos que investigaram os efeitos da suplementacao de creatina na forca e hipertrofia; e 2) reunir as evidencias acerca dos possiveis mecanismos responsaveis pelo aumento de forca e massa magra como consequencia desse suplemento, enfatizando os mais recentes achados e as perspectivas sobre o tema. De fato, existem fortes evidencias demonstrando que a suplementacao de creatina e capaz de promover aumentos de forca e hipertrofia. Os efeitos desse suplemento sobre a retencao hidrica, o balanco proteico, a expressao de genes/proteinas associados a hipertrofia e ativacao de celulas satelites, podem explicar as adaptacoes musculoesqueleticas observadas. Diante desses achados, os potenciais efeitos terapeuticos desse suplemento emergem como um futuro e promissor campo de estudo.

Bioenergetics and Neuromuscular Determinants of the Time to Exhaustion at Velocity Corresponding to V[Combining Dot Above]O2max in Recreational Long-Distance Runners

Abstract Bertuzzi, R, Bueno, S, Pasqua, LA, Acquesta, FM, Batista, MB, Roschel, H, Kiss, MAPDM, Serrão, JC, Tricoli, V, and Ugrinowitsch, C. Bioenergetics and neuromuscular determinants of the time to exhaustion at velocity corresponding to V[Combining Dot Above]O2max in recreational long-distance runners. J Strength Cond Res 26(8): 2096–2102, 2012—The purpose of this study was to investigate the main bioenergetics and neuromuscular determinants of the time to exhaustion (Tlim) at the velocity corresponding to maximal oxygen uptake in recreational long-distance runners. Twenty runners performed the following tests on 5 different days: (a) maximal incremental treadmill test, (b) 2 submaximal tests to determine running economy and vertical stiffness, (c) exhaustive test to measured the Tlim, (d) maximum dynamic strength test, and (e) muscle power production test. Aerobic and anaerobic energy contributions during the Tlim test were also estimated. The stepwise multiple regression method selected 3 independent variables to explain Tlim variance. Total energy production explained 84.1% of the shared variance (p = 0.001), whereas peak oxygen uptake (V[Combining Dot Above]O2peak) measured during Tlim and lower limb muscle power ability accounted for the additional 10% of the shared variance (p = 0.014). These data suggest that the total energy production, V[Combining Dot Above]O2peak, and lower limb muscle power ability are the main physiological and neuromuscular determinants of Tlim in recreational long-distance runners.

Motor Physical Therapy Affects Muscle Collagen Type I and Decreases Gait Speed in Dystrophin-Deficient Dogs

Golden Retriever Muscular Dystrophy (GRMD) is a dystrophin-deficient canine model genetically homologous to Duchenne Muscular Dystrophy (DMD) in humans. Muscular fibrosis secondary to cycles of degeneration/regeneration of dystrophic muscle tissue and muscular weakness leads to biomechanical adaptation that impairs the quality of gait. Physical therapy (PT) is one of the supportive therapies available for DMD, however, motor PT approaches have controversial recommendations and there is no consensus regarding the type and intensity of physical therapy. In this study we investigated the effect of physical therapy on gait biomechanics and muscular collagen deposition types I and III in dystrophin-deficient dogs. Two dystrophic dogs (treated dogs-TD) underwent a PT protocol of active walking exercise, 3×/week, 40 minutes/day, 12 weeks. Two dystrophic control dogs (CD) maintained their routine of activities of daily living. At t0 (pre) and t1 (post-physical therapy), collagen type I and III were assessed by immunohistochemistry and gait biomechanics were analyzed. Angular displacement of shoulder, elbow, carpal, hip, stifle and tarsal joint and vertical (Fy), mediolateral (Fz) and craniocaudal (Fx) ground reaction forces (GRF) were assessed. Wilcoxon test was used to verify the difference of biomechanical variables between t0 and t1, considering p<.05. Type I collagen of endomysium suffered the influence of PT, as well as gait speed that had decreased from t0 to t1 (p<.000). The PT protocol employed accelerates morphological alterations on dystrophic muscle and promotes a slower velocity of gait. Control dogs which maintained their routine of activities of daily living seem to have found a better balance between movement and preservation of motor function.

Effects of Strength Training Associated With Whole-Body Vibration Training on Running Economy and Vertical Stiffness

Abstract Roschel, H, Barroso, R, Tricoli, V, Batista, MAB, Acquesta, FM, Serrão, JC, and Ugrinowitsch, C. Effects of strength training associated with whole-body vibration training on running economy and vertical stiffness. J Strength Cond Res 29(8): 2215–2220, 2015—Running economy (RE) is defined as the energy cost to maintain a submaximal running velocity and seems to be affected by individuals neuromuscular characteristics, such as stiffness level. Both resistance training (RT) and whole-body vibration training added to RT (WBV + RT) have been shown to influence those characteristics. Thus, it is conceivable that RT and WBV + RT could also affect RE. The objective of this study was to investigate if a 6-week training period of RT and WBV + RT influences RE and vertical stiffness (VS). Fifteen recreational runners were divided into RT or WBV + RT groups. Running economy, VS, and lower-limb maximum dynamic strength (1 repetition maximum [1RM] half-squat) were assessed before and after the 6-week training period. There was a main time effect for 1RM, but no other statistically significant difference was observed. Neither conventional RT nor RT performed on a WBV platform improved VS and RE in recreational long distance runners. It is possible that movement velocity was rather low, and utilization of stretch-shortening cycle might have been compromised, impairing any expected improvement in RE.

Effects of replica running shoes upon external forces and muscle activity during running

Abstract Twelve participants ran (9 km · h−1) to test two types of running shoes: replica and original shoes. Ground reaction force, plantar pressure and electromyographic activity were recorded. The shoes were tested randomly and on different days. Comparisons between the two experimental conditions were made by analysis of variance (ANOVA) test (P ≤ 0.05). The time to first peak, loading rate of the first peak and impulse of the first 75 ms of stance were significantly different between the shoes (P ≤ 0.05), revealing an increase of impact forces for the replica shoes. The peak plantar pressure values were significantly higher (P ≤ 0.05) when wearing replica shoes. During running, the contact area was significantly smaller (P ≤ 0.05) for the replica shoe. The electromyographic activity of the analysed muscles did not show changes between the two shoes in running. These findings suggest that the use of replica running shoes can increase the external load applied to the human body, but may not change the muscle activity pattern during locomotion. This new mechanical situation may increase the risk of injuries in these movements.

Desenvolvimento de um método de familiarização individualizado para saltos verticais

OBJECTIVE: The aim of the present study was to propose an individualized familiarization method for vertical jumps and to verify its effect on intra-subject variability. METHODS: Fifty three men (mean ± S.D.; age 23.5 ± 3.3; height 1.76 ± 0.08 m; mass 72.8 ± 8.6 Kg; body fat 12.9 ± 5.2%) performed successive jumps to reach the proposed stability level. After 48 hours, this process was repeated and the stability between the days was verified; if necessary, more sessions were performed. The stability level was determined by a Z-Test with a confidence interval of 95%. After the familiarization process, two additional experimental sessions were performed in order to determine the reliability of the performance in the Squat Jump (SJ) and the Countermovement Jump (CMJ). The coefficient of variation and standard error of measurement were determined individually (CVi and SEMi). A paired T-Test was performed to verify differences in the CVi and SEMi before and after the familiarization process. RESULTS: The CVi presented a significant reduction after the familiarization process (p < 0.001), changing from 5.01 ± 2.40% to 2.95 ± 0.89% in the SJ. The CVi also changed in the CMJ (from 4.50 ± 2.19% to 2.58 ± 0.81%). The same also occurred with the SEMi in both the SJ and the CMJ, changing from 1.29 ± 0.53 cm to 0.83 ± 0.25 cm in the SJ and from 1.35 ± 0.51cm to 0.83 ± 0.26 cm in the CMJ. CONCLUSION: The proposed individualized familiarization method significantly decreased intra-subject variability, which allows for a higher statistical power in the laboratorial setting and a greater sensitivity for performance monitoring tools.