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 (VO(2)peak) 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 VO(2)peak 56.7 ± 4.4 ml·kg·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.

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.

The aim of this study was to use technical skill and physical performance and coaches’ rankings to predict the defensive performance of junior soccer players. Twenty-one male players (mean age 17.2 years, SD = 1.1) were recruited from the Londrina Junior Team Football Academy in Brazil. Data were collected during regular training sessions. After participants had warmed up, players were asked to either dribble the ball or sprint through five custom circuits that varied in average curvature (0–1.37 radians.m-1). In addition, four coaches were asked to rank the players from best to worst in defensive ability. Dribbling, sprinting, and coaches’ rankings were then compared with defending performance as assessed in the one vs. one competitions (N = 1090 paired-trials: 40–65 trials per individual), in which they acted as defender or attacker in turn. When defending, the objective was to steal the ball or prevent the attacker from running around them with the ball into a scoring zone. Testing occurred over three days. Overall, dribbling performance (r = 0.56; P = 0.008) and coaches’ ranking (r = 0.59; P = 0.004) were significantly related to defensive ability; sprinting performance was not (r = 0.20; P = 0.38). Though dribbling performance and coaches’ ranking each explained 30% and 37% of the variance in defensive performance, respectively, the two predictors were not related (r = 0.27; P = 0.23), so combined these traits explained more than half the variance in defensive performance. In conclusion, the current study demonstrates that including only one metric of closed-skill performance—dribbling speed—doubles the ability of coaches to identify their best defensive players in one vs. one scenarios.

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% W(max)). 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.

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 supramaximal constant load dynamic exercise (110% VO(2peak)). The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in supramaximal 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.

No abstract

The aim of the study was to investigate the effects of caffeine intake on anaerobic performance and rate of muscle fatigue in young men and women. Methods: Fourteen recreationally active college students volunteered to the study (7 male, 29.1 ± 2.8 у and 7 female, 22.5 ± 2.9 y) (73.06 ± 13.08 Kg, 173.00 ± 6.90 cm, 24.08 ± 3.01 Kg/m 2). The participants performed the Wingate Test (WT) to evaluate the anaerobic performance in two conditions: caffeine (CAF), ingesting 6mgKg-1 of caffeine, and placebo (PL), in random order. The variables analyzed during the WT were the Relative Peak Power (W-Kg-1) (RPP), Relative Mean Power (WKg-1) (RMP), Fatigue Index (%) (Fl) and Peak Power Instant (s) (PPI). EMG signals were analyzed using the Normalized Median Frequency (NMF) to determine the rate of muscle fatigue of the superficial muscles of the Quadriceps Femoris (QF), Rectus Femoris (RF), Vastus Medialis (VM) and Vastus Lateralis (VL). Data analysis was performed using the Student's t test and the two-way AN OVA for repeated measures, followed by the Sheffe post-hoc to compare the results. Results: Caffeine intake had no effect on anaerobic performance parameters (RPP, RMP, Fl and PPI) when compared with placebo (p > 0.05). The rate of muscle fatigue did not change with caffeine intake in the muscles studied (p > 0.05). Conclusions: Although caffeine may influence endurance and power in short-term, intense exercise; we did not observe such effects in the variables measured in this study.

Efeito da oclusão temporal na ação de ataque IntroduçãoEfeito da oclusão temporal na ação de ataque sobre a tomada de decisão defensiva na modalidade de voleibol CDD. 20.ed. 152 ResumoO presente estudo analisou o efeito da oclusão temporal na cortada do voleibol sobre a tomada de decisão defensiva em atletas com diferentes níveis de experiência. Os participantes foram divididos em três grupos: adulto (GAD; n = 16), infanto/mirim (GIM; n =16) e adulto novato (GNO; n = 16). Imagens da fi nalização 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) após o contato do atacante com a bola. Ao assistirem os vídeos editados, os participantes deveriam informar o local de aterrissagem da bola seguido da confi ança com a qual emitiam suas respostas. Foi mensurada a precisão na predição da trajetória da bola (acerto/erro) e a confi ança da resposta (escala Likert 1-5). Quanto à frequência de acertos, o grupo GAD (X = 63,67 ± 10,38%) apresentou maior frequência de acertos que GIM (X = 55,46 ± 10,17%) em OT2 (p = 0,001). A frequência de acertos de GAD (X = 79,29 ± 10,38%) também foi maior que a de GNO (X = 71,87 ± 10,43%) em OT3 (p = 0,012). As condições mostraram-se diferentes entre si (Bonferroni's p < 0,005), com a frequência de acertos aumentando de OT1 (X = 36,06 ± 12,44%) à OT5 (X = 98,17 ± 4,81%). Para confi ança, GAD e GIM apresentaram-se mais confi antes que GNO (Bonferroni's p < 0,016) em OT1, OT2, OT3. Novamente, as condições diferiram entre si (Bonferroni's p < 0,005), com os grupos mostrando-se mais confi antes em OT5. Concluiu-se que, independente da experiência, os grupos se mostraram capazes de predizer a localização de aterrissagem da bola. Contudo, grupos com maior experiência mostraram-se superior quanto à sua capacidade antecipatória.PALAVRAS-CHAVE: Tomada de decisão; Antecipação; Padrão de reconhecimento visual; Voleibol.Por muito tempo, no esporte, acreditou-se que a superioridade individual devia-se a uma espécie de seleção natural, na qual o sucesso dos atletas adviria por um sistema nervoso mais desenvolvido 1 . Contudo, nas últimas três décadas, estudiosos no esporte têm fornecido evidências de que, em modalidades esportivas que apresentam restrições temporais, o desempenho habilidoso não se refere apenas à realização precisa da ação motora 2 . Assim, diversas modalidades esportivas foram investigadas, tais com: hóquei de campo 1 , diferentes esportes com raquete 3-10 , futebol 11 , cricket 12 , rúgbi 13 , e voleibolquadra e praia 2,14-15 .A partir disso, houve uma crescente conscientização no que diz respeito à importância de habilidades cognitivas perceptuais para o desempenho em alto nível 16 . Tais habilidades fazem referência à capacidade de identi car e adquirir informações ambientais a m de selecionar e executar respostas apropria...