Leandro Ricardo Altimari

Fourier and wavelet spectral analysis of EMG signals in supramaximal constant load dynamic 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 maximal constant load dynamic exercise (100% Wmax). The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in maximal constant load dynamic exercise (P>0.05). However, the results of the variance was significantly lower for at least one of the muscles studied 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.

Improving Cycling Performance: Transcranial Direct Current Stimulation Increases Time to Exhaustion in Cycling.

The central nervous system seems to have an important role in fatigue and exercise tolerance. Novel noninvasive techniques of neuromodulation can provide insights on the relationship between brain function and exercise performance. The purpose of this study was to determine the effects of transcranial direct current stimulation (tDCS) on physical performance and physiological and perceptual variables with regard to fatigue and exercise tolerance. Eleven physically active subjects participated in an incremental test on a cycle simulator to define peak power output. During 3 visits, the subjects experienced 3 stimulation conditions (anodal, cathodal, or sham tDCS—with an interval of at least 48 h between conditions) in a randomized, counterbalanced order to measure the effects of tDCS on time to exhaustion at 80% of peak power. Stimulation was administered before each test over 13 min at a current intensity of 2.0 mA. In each session, the Brunel Mood State questionnaire was given twice: after stimulation and after the time-to-exhaustion test. Further, during the tests, the electromyographic activity of the vastus lateralis and rectus femoris muscles, perceived exertion, and heart rate were recorded. RM-ANOVA showed that the subjects performed better during anodal primary motor cortex stimulation (491 ± 100 s) compared with cathodal stimulation (443 ± 11 s) and sham (407 ± 69 s). No significant difference was observed between the cathodal and sham conditions. The effect sizes confirmed the greater effect of anodal M1 tDCS (anodal x cathodal = 0.47; anodal x sham = 0.77; and cathodal x sham = 0.29). Magnitude-based inference suggested the anodal condition to be positive versus the cathodal and sham conditions. There were no differences among the three stimulation conditions in RPE (p = 0.07) or heart rate (p = 0.73). However, as hypothesized, RM- ANOVA revealed a main effect of time for the two variables (RPE and HR: p < 0.001). EMG activity also did not differ during the test accross the different conditions. We conclude that anodal tDCS increases exercise tolerance in a cycling-based, constant-load exercise test, performed at 80% of peak power. Performance was enhanced in the absence of changes in physiological and perceptual variables.

Back muscle fatigue of younger and older adults with and without chronic low back pain using two protocols: A case-control study.

The purpose of this study was to compare back muscle fatigue of younger and older participants with and without chronic low back pain (CLBP). Twenty participants without and 20 with nonspecific CLBP participated in this study. Each group contained 10 younger (50% males; mean age: 31 ± 6 yrs) and 10 older adults (50% males; age mean: 71 ± 7 yrs). Two isometric fatigue protocols were presented randomly: (1) to maintain the unsupported trunk at the horizontal position while on a 45° Roman chair for a minute, and (2) to maintain a 10% of body weight box close to the trunk in the upright position for a minute. Surface electromyography (EMG) signals from the back (multifidus and iliocostalis) and one hip (biceps femoris) muscles were recorded bilaterally, and the median frequency fatigue estimate from linear regression slopes of the EMG time-series was computed. There were no significant (P > 0.05) age effects, and group-by-age interaction in both isometric and functional fatigue tasks. However, the CLBP groups (both younger and old) displayed more back fatigue than people without CLBP in both fatigue protocols (P < 0.01; effect size varying of d = 0.17-0.32). This study was sensitive to discriminate that individuals with CLBP did present significantly more pronounced EMG back fatigue than people without CLBP, in both younger and older adults. These results have significant clinical implications for low back pain rehabilitation programs with regard to endurance assessment in both younger and older.

Effect of strength training on rate of force development in older women.

We analyzed the effect of an 8-week strength training (ST) program on the rate of force development (RFD) and electromyographic activity (EMG) in older women. Seventeen women (M age = 63.4 years, SD = 4.9) without previous ST experience were randomly assigned to either a control (n = 7) or training (n = 10) group. A leg-press isometric test was used for assessment. ST (three sessions/ week, three sets of 10–12 repetition maximum, five different exercises) induced significant increases (p < .05) on peak RFD (48.4%) and on RFD and EMG of vastus medialis at time intervals of 0–50, 0–100, 0–150, and 0–200 ms (41.1–69.2% and 43.8– 64.3%, respectively). Therefore, ST resulted in favorable changes in neuromuscular responses in older women.

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.

Variação do equilíbrio muscular durante uma temporada em jogadores de futebol categoria sub-20

The objective of the present study was to evaluate the muscular balance of knee flexors and extensors (RFE) in under-20 soccer players during a training season. 15 under-20 subjects from the Ponte Preta Athletic Association of Campinas participated in a 29 week macrocycle preparation (MP), composed of preparatory and competitive periods which were divided into four mesocycles: general stage (M1), special stage (M2), pre-competitive stage (M3) and competitive stage (M4). RFE of both members was determined with the torque peak (TP) obtained in isokinetic dynamometer in three consecutive sets of five repetitions of 60 degrees/s. Isokinetic evaluation was accomplished in four stages along the MP at the end of each mesocycle (M1, M2, M3, and M4). Statistic analysis was performed using the Friedman test with repeated measures, followed by Wilcoxon test and Mann-Whitney U test, with significance level of p<0.05. TP of knee flexors muscles in both members were greater in M2 and M3 than in M1 and M4. TP of knee extensors in M1 was significantly inferior than the other stages of the study (M2, M3, and M4), in both members. RFE, in both members, was inferior in M1 when compared to M2 and M3. RFE comparison among members did not reveal significant differences in any moment of the study (M1, M2, M3, and M4). The results indicated the existence of alterations in the size of RFE; within normality though, and maintenance of the proportionality among members along the MP. These results suggest that there are not sensitive periods to the occurrence of injuries due to muscular imbalances along MP in under-20 soccer players.

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.

Brain mechanisms that underlie the effects of motivational audiovisual stimuli on psychophysiological responses during exercise

Motivational audiovisual stimuli such as music and video have been widely used in the realm of exercise and sport as a means by which to increase situational motivation and enhance performance. The present study addressed the mechanisms that underlie the effects of motivational stimuli on psychophysiological responses and exercise performance. Twenty-two participants completed fatiguing isometric handgrip-squeezing tasks under two experimental conditions (motivational audiovisual condition and neutral audiovisual condition) and a control condition. Electrical activity in the brain and working muscles was analyzed by use of electroencephalography and electromyography, respectively. Participants were asked to squeeze the dynamometer maximally for 30s. A single-item motivation scale was administered after each squeeze. Results indicated that task performance and situational motivational were superior under the influence of motivational stimuli when compared to the other two conditions (~20% and ~25%, respectively). The motivational stimulus downregulated the predominance of low-frequency waves (theta) in the right frontal regions of the cortex (F8), and upregulated high-frequency waves (beta) in the central areas (C3 and C4). It is suggested that motivational sensory cues serve to readjust electrical activity in the brain; a mechanism by which the detrimental effects of fatigue on the efferent control of working muscles is ameliorated.

Resistance training promotes increase in intracellular hydration in men and women

Abstract The main purpose of the present study was to investigate the effect of 16 weeks of resistance training (RT) on body water in men and women. Thirty men (22.7 ± 4.4 years, 68.4 ± 9.0 kg and 174.5 ± 6.6 cm) and 34 women (22.7 ± 4.1 years, 58.8 ± 11.9 kg and 162.6 ± 6.2 cm) underwent progressive RT for 16 weeks (2 phases, 8 weeks each), 3 times per week, that consisted of 10–12 whole body exercises with 3 sets of 8–12 repetitions maximum. Total body water, TBW (intracellular water, ICW and extracellular water, ECW compartments) and skeletal muscle mass (SMM) were assessed using a spectral bioelectrical impedance device (Xitron 4200 Bioimpedance Spectrum Analyzer). TBW, ICW compartment and SMM increased significantly (P < 0.05) over time in men (+7.5%, +8.2% and +4.2%, respectively) and women (+7.6%, +11.0% +3.9%, respectively), with no sex by time interaction (P > 0.05). We conclude that progressive RT promotes an increase in body water, principally by intracellular content; however, the hydration status is not influenced by sex.