Evaluation of muscular fatigue thresholds in athletes performing short-duration and explosive exercises is difficult because classic parameters do not suffer large variations. Therefore, the aim of this study was to develop a new method to estimate the fatigue threshold in single muscles. Our approach is based on electromyographic data recorded during a maximum incremental strength test until the one repetition maximum is reached. Ten men and 10 women performed a half-squat strength test consisting of five incremental intensities of one repetition maximum. Neither heart rate nor blood lactate concentrations showed significant differences at the various intensities tested. Surface electromyographic activities of vastus lateralis, vastus medialis, and rectus femoris were recorded, finding a break point corresponding to the fatigue threshold occurring in men at 70.74%, 71.48%, and 72.52% of one repetition maximum, respectively. In women, break-point values were 76.66% for vastus lateralis, 76.27% for vastus medialis, and 72.10% for rectus femoris. In conclusion, surface electromyography could be a useful, rapid, and noninvasive tool to determine the fatigue threshold of independent muscles during a maximal half-squat strength test.
Jerónimo Aragón-Vela, Yaira Barranco-Ruiz, Cristina Casals-Vázquez, Julio Plaza-Díaz, Rafael A. Casuso, Luis Fontana and Jesús F. Rodríguez Huertas
Edgard Melo Keene von Koenig Soares, Guilherme E. Molina, Daniel Saint Martin, João Luís A. E. Sadat P. Leitão, Keila E. Fontana, Luiz F. Junqueira Jr., Timóteo Leandro de Araújo, Sandra Mahecha Matsudo, Victor K. Matsudo and Luiz Guilherme Grossi Porto
Background: The World Health Organization recommends 150 minutes of moderate to vigorous physical activity (PA) throughout the week. However, the weekly frequency of PA and how to combine moderate and vigorous PA to define who reaches the recommended PA are controversial. PA level might be highly different based on the recommendation and/or the criteria employed. Methods: Demographic data and PA level evaluated by International Physical Activity Questionnaire from 3 random and representative samples from 1 state, 1 city, and 1 local organization in Brazil were analyzed (n = 2961). Nine criteria from different recommendations were used to define PA level. Prevalence estimates and 95% confidence intervals of sufficient PA were calculated for each criterion and compared with the referent (World Health Organization guideline). Total agreement, sensitivity, and specificity were also calculated with 95% confidence interval. Results: When a weekly frequency of PA was required, the prevalence of sufficient PA decreased by 11% (P < .05). For all criteria, doubling the vigorous PA minutes was similar to simply adding them to moderate PA. These findings are consistent regardless of sex, age, and educational level. Conclusion: Prevalence estimates and agreement between different PA recommendations were significantly affected when a minimum frequency was required but did not change when vigorous PA minutes were doubled.