Antonio Carlos de Moraes

Cafeína e performance em exercícios anaeróbios

The ergogenic effects of caffeine on performance in anaerobic activites are not clear yet, so are the mechanisms involved in this type of physical effort. The theories that have been trying to explain the ergogenic effects of caffeine during anaerobic activities are related to the effect of caffeine in some portion of the central nervous system (CNS), the propagation of neural signs between brain and neuromuscular junction, and also to the effect of caffeine on the skeletal muscle, facilitating the stimulation-contraction of the skeletal muscle. Some studies have been indicating increases of muscular strength accompanied by greater resistance to the installation of the process of muscular fatigue after caffeine ingestion. It has been suggested that it happens much more by the direct action of caffeine in CNS than by its action at peripherical level. Regarding maximum and submaximum exercises of short duration, the studies have been controversial, although most of them indicates that caffeine seems to improve the performance significantly in maximum exercises of short duration (<5 min), when not preceded by sub maximum prolonged exercises. However, these results need to be confirmed, as well as the mechanisms of action of caffeine in these types of efforts.

Electromyographic activity and rate of muscle fatigue of the quadriceps femoris during cycling exercise in the severe domain.

Camata, TV, Altimari, LR, Bortolotti, H, Dantas, JL, Fontes, EB, Smirmaul, BPC, Okano, AH, Chacon-Mikahil, MPT, and Moraes, AC. Electromyographic activity and rate of muscle fatigue of the quadriceps femoris during cycling exercise in the severe domain. J Strength Cond Res 25(9): 2537-2543, 2011—This study compared the activation pattern and the fatigue rate among the superficial muscles of the quadriceps femoris (QF) during severe cycling exercise. Peak oxygen consumption (&OV0312;o2peak) and maximal accumulated oxygen Deficit (MAOD) were established by 10 well-trained male cyclists (27.5 ± 4.1 years, 71.0 ± 10.3 kg, 173.4 ± 6.6 cm, mean &OV0312;o2peak 56.7 ± 4.4 ml·kg−1·min−1, mean MAOD 5.7 ± 1.1 L). Muscle activity (electromyographic [EMG] signals) was obtained during the supramaximal constant workload test (MAOD) and expressed by root mean square (RMS) and median frequency (MF slope). The RMS of the QF, vastus lateralis (VL) and vastus medialis (VM) muscles were significantly higher than at the beginning after 75% of exercise duration, whereas for the rectus femoris (RF), this was observed after 50% of exercise duration (p ≤ 0.05). The slope of the MF was significantly higher in the RF, followed by the VL and VM (−3.13 ± 0.52 vs. −2.61 ± 0.62 vs. −1.81 ±0.56, respectively; p < 0.05). We conclude that RF may play an important role in limiting performance during severe cycling exercise.

Fourier and wavelet spectral analysis of EMG signals in isometric and dynamic maximal effort exercise

Frequency domain analyses of changes in electromyographic (EMG) signals over time are frequently used to assess muscle fatigue. Fourier based approaches are typically used in these analyses, yet Fourier analysis assumes signal stationarity, which is unlikely during dynamic contractions. Wavelet based methods of signal analysis do not assume stationarity and may be more appropriate for joint time-frequency domain analysis. The purpose of this study was to compare Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) in assessing muscle fatigue in isometric and dynamic exercise. The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in isometric and dynamic exercise (P>0.05). However, the results of the variance was lower for both types of exercise in CWT compared to STFT (P<0.05) indicating more variability in the EMG signal analysis using STFT. Thus, the stationarity assumption may not be the sole factor responsible for affecting the Fourier based estimates.

Comparação entre limiar anaeróbio determinado por variáveis ventilatórias e pela resposta do lactato sanguíneo em ciclistas

Muitas investigacoes tem demonstrado que a coincidencia entre os limiares ventilatorios e os limiares que se utilizam da resposta do lactato nem sempre ocorre, sugerindo que nao existe relacao entre causa e efeito entre os fenomenos. Dessa forma, o presente estudo teve como objetivos comparar e correlacionar os valores de consumo de oxigenio (VO2), potencia (W) e frequencia cardiaca (FC) obtidos por protocolos de determinacao do limiar ventilatorio (LV) e limiar anaerobio individual (IAT). A amostra foi constituida por oito ciclistas de niveis paulista e nacional (idade: 27,88 ± 8,77 anos; massa corporal: 65,19 ± 4,40kg; estatura: 169,31 ± 5,77cm). O IAT foi determinado iniciando-se com aquecimento de tres minutos a 50W com aumentos progressivos de 50W.3min-1 ate a exaustao voluntaria, com as coletas de sangue aos 20 segundos finais de cada estagio e durante a recuperacao. Para a determinacao do LV, utilizou-se o mesmo protocolo adotado para a determinacao do IAT, porem, sem efetuar as coletas de sangue. O LV foi identificado pelas mudancas da ventilacao pulmonar e dos equivalentes ventilatorios de O2 e CO2. O teste t de Student nao revelou diferencas estatisticamente significantes em nenhuma das variaveis obtidas. As associacoes encontradas foram altas e significativas. O VO2 (ml.kg-1.min-1), P (W) e FC (bpm) correspondente ao LV e IAT, e as associacoes entre as variaveis foram, respectivamente, de: 48,00 ± 3,82 vs 48,08 ± 3,71 (r = 0,90); 256,25 ± 32,04 vs 246,88 ± 33,91 (r = 0,84); 173,75 ± 9,18 vs 171,25 ± 12,02 (r = 0,97). De acordo com os resultados obtidos, pode-se concluir que o IAT e o LV produzem valores semelhantes de VO2, W e FC, o que favorece a adocao do LV por ser um metodo nao-invasivo para determinacao do limiar anaerobio em ciclistas.

Comparison between anaerobic threshold determined by ventilatory variables and blood lactate response in cyclists

Muitas investigacoes tem demonstrado que a coincidencia entre os limiares ventilatorios e os limiares que se utilizam da resposta do lactato nem sempre ocorre, sugerindo que nao existe relacao entre causa e efeito entre os fenomenos. Dessa forma, o presente estudo teve como objetivos comparar e correlacionar os valores de consumo de oxigenio (VO2), potencia (W) e frequencia cardiaca (FC) obtidos por protocolos de determinacao do limiar ventilatorio (LV) e limiar anaerobio individual (IAT). A amostra foi constituida por oito ciclistas de niveis paulista e nacional (idade: 27,88 ± 8,77 anos; massa corporal: 65,19 ± 4,40kg; estatura: 169,31 ± 5,77cm). O IAT foi determinado iniciando-se com aquecimento de tres minutos a 50W com aumentos progressivos de 50W.3min-1 ate a exaustao voluntaria, com as coletas de sangue aos 20 segundos finais de cada estagio e durante a recuperacao. Para a determinacao do LV, utilizou-se o mesmo protocolo adotado para a determinacao do IAT, porem, sem efetuar as coletas de sangue. O LV foi identificado pelas mudancas da ventilacao pulmonar e dos equivalentes ventilatorios de O2 e CO2. O teste t de Student nao revelou diferencas estatisticamente significantes em nenhuma das variaveis obtidas. As associacoes encontradas foram altas e significativas. O VO2 (ml.kg-1.min-1), P (W) e FC (bpm) correspondente ao LV e IAT, e as associacoes entre as variaveis foram, respectivamente, de: 48,00 ± 3,82 vs 48,08 ± 3,71 (r = 0,90); 256,25 ± 32,04 vs 246,88 ± 33,91 (r = 0,84); 173,75 ± 9,18 vs 171,25 ± 12,02 (r = 0,97). De acordo com os resultados obtidos, pode-se concluir que o IAT e o LV produzem valores semelhantes de VO2, W e FC, o que favorece a adocao do LV por ser um metodo nao-invasivo para determinacao do limiar anaerobio em ciclistas.

Electromechanical delay of the knee extensor muscles: comparison among young, middle-age and older individuals.

The aim of this study was to investigate the effects of the ageing process in the electromechanical delay (EMD), rate of torque development (RTD) and peak torque (PT) of the knee extensor muscles. The volunteers were assigned to three groups: young group (YG – 23·44 ± 4·74 years, 78·14 ± 15·11 kg, 1·72 ± 0·05 m), middle‐aged group (MAG – 49·56 ± 6·06 years, 72·01 ± 14·07 kg, 1·67 ± 0·06 m) and elderly group (EG – 68·67 ± 9·06 years, 67·96 ± 7·60 kg, 1·64 ± 0·07 m). The PT and RTD were assessed during maximal voluntary ballistic isometric contractions (MVBIC) in the isokinetic dynamometer. Muscle electrical activity was recorded (EMG) during MVBIC in the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles. The EMD was calculated during the MVBIC, through the time interval between the EMG onset and torque onset. The PT and RTD were higher in the YG than in the MAG (P = 0·02; P = 0·01, respectively) and in the EG (P = 0·002; P = 0·0004, respectively). There were no significant differences in EMD among the three age groups for the VL, VM and RF (P>0·05) muscles. We conclude that age affects the PT and RTD, but not EMD of the VL, VM and RF muscles.

RELATIONSHIP BETWEEN WORKLOAD AND NEUROMUSCULAR ACTIVITY IN THE BENCH PRESS EXERCISE

Objective: To investigate the relationship between strength and electromyographic (EMG) signal in different intensities in the bench press exercise. Methods: Eleven healthy resistance trained men (22.8 ± 3.5) participated into the present study. Maximal isometric strength was determined in the bench press exercise using a load cell. Muscle activation was assessed using surface elec- tromyography (EMG) signals from the muscles pectoralis major, anterior deltoid and posterior deltoid at intensities ranging to 60-90% of maximal voluntary contraction (MVC), in the bench press exercise. This procedure allowed the analysis of the strength/EMG relationship. Results: In all muscles assessed, there were significant differences in the normalized muscle activation between the intensities of 60 and 70% of the MVC, as well as between 70 and 80% (P<0.05), while there were no differences between 80 and 90% of MVC. In addition, there were significant correlations between strength and EMG signals for the muscles pectoralis major (r=0.43, P=0.04), anterior deltoid (r=0.52, P=0.01), and posterior deltoid (r=0.32, P=0.046). Conclusions: These results suggest that levels of muscle activation near to maximal are obtained at the intensity of 80 of MVC and no additional motor unit recruitment are achieved at 90% of MVC.

O nível de treinamento não influencia a percepção subjetiva de esforço durante um teste incremental

Different training levels, combined with experience in performing exhaustive exercise, may produce different sensations of fatigue. The objective of this study was to compare the rating of perceived exertion (RPE) between cyclists and non-cyclists during a maximal incremental test (ITMAX). Twenty-three subjects were recruited and divided into a cyclist group (CG) (n = 12; age: 26.5 ± 4.7 years, body weight: 68.2 ± 11kg, height: 176 ± 8.6 cm) and a non-cyclist group (NCG) (n = 11; 25.2 ± 4.0 years, body weight: 72.9 ± 9 kg, height: 175.1 ± 6.3 cm). All subjects performed an ITMAX until exhaustion on a cycling simulator, starting at 0 W and with increments of 20 W.min-1. RPE was measured at 30-second intervals during ITMAX and the maximal power output (PMAX) of each subject was also recorded. The total time of each test was normalized to the percentage of completed trial (10% to 100%, intervals of 10%), and the corresponding RPE was recorded. PMAX was 368 ± 12.7 W and 256 ± 11.2 W for CG and NCG, respectively (P < 0.01). No significant difference in median RPE was observed between groups at any time point. In conclusion, RPE responses did not differ between CG and NCG during ITMAX, suggesting that training level does not influence RPE.

Influence of Different Strategies of Treatment Muscle Contraction and Relaxation Phases on EMG Signal Processing and Analysis During Cyclic Exercise

© 2012 Altimari et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Influence of Different Strategies of Treatment Muscle Contraction and Relaxation Phases on EMG Signal Processing and Analysis During Cyclic Exercise

Respostas neuromusculares dos membros inferiores durante protocolo intermitente de saltos verticais em voleibolistas

The purpose of this study was to analyze the performance and the electromyographic responses of the muscles Rectus Femoris, Biceps Femoris and Gastrocnemius Medialis during vertical jumping protocol. Participated 13 female volleyball players (15,6 ± 0,9 years). Initially was performed a protocol of maximum power (three maximum jumps), followed by resistance jumps protocol (cycles of three maximum jumps in about 10 seconds (s) - one jump every three s, with recovery of 15s. The duration of resistance protocol was 20 minutes. Technique used was countermovement jump without the aid of arms on a mat of contact. The data collected during the jumps were divided into four periods containing 12 cycles each. The results showed a decrease in the height of the jumps of about 1,3cm between the periods from 1 to 4, and this decrease was more significant in the 3rd and 4th periods compared with the 1st and 2nd. However, with respect to the variables RMS and FM, a change did not occur in the electromyographic responses between muscles and periods. It was concluded that fatigue may depend of the psychophysiological variables, the level of the CNS, which also influence the performance.