Thiago Viana Camata

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.

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.

Efeito da oclusão temporal na ação de ataque sobre a tomada de decisão defensiva na modalidade de voleibol

O presente estudo analisou o efeito da oclusao temporal na cortada do voleibol sobre a tomada de decisao defensiva em atletas com diferentes niveis de experiencia. Os participantes foram divididos em tres grupos: adulto (GAD; n = 16), infanto/mirim (GIM; n =16) e adulto novato (GNO; n = 16). Imagens da finalizacao de jogadas de ataque realizadas por quatro atletas foram editadas em cinco diferentes momentos: (OT1) a 399 ms (12 quadros) antes do contato do atacante com a bola; (OT2) a 266 ms (oito quadros) antes; (OT3) a 133 ms (quatro quadros) antes; (OT4) no momento do contato atacante/bola e; (OT5) a 133 ms (quatro quadros) apos o contato do atacante com a bola. Ao assistirem os videos editados, os participantes deveriam informar o local de aterrissagem da bola seguido da confianca com a qual emitiam suas respostas. Foi mensurada a precisao na predicao da trajetoria da bola (acerto/erro) e a confianca da resposta (escala Likert 1-5). Quanto a frequencia de acertos, o grupo GAD (X = 63,67 ± 10,38%) apresentou maior frequencia de acertos que GIM (X = 55,46 ± 10,17%) em OT2 (p = 0,001). A frequencia de acertos de GAD (X = 79,29 ± 10,38%) tambem foi maior que a de GNO (X = 71,87 ± 10,43%) em OT3 (p = 0,012). As condicoes mostraram-se diferentes entre si (Bonferronis p < 0,005), com a frequencia de acertos aumentando de OT1 (X = 36,06 ± 12,44%) a OT5 (X = 98,17 ± 4,81%). Para confianca, GAD e GIM apresentaram-se mais confiantes que GNO (Bonferronis p < 0,016) em OT1, OT2, OT3. Novamente, as condicoes diferiram entre si (Bonferronis p < 0,005), com os grupos mostrando-se mais confiantes em OT5. Concluiu-se que, independente da experiencia, os grupos se mostraram capazes de predizer a localizacao de aterrissagem da bola. Contudo, grupos com maior experiencia mostraram-se superior quanto a sua capacidade antecipatoria.