Publicação
Effects of attentional focus on the regulation of torque variability
| Resumo: | In strength training, especially in rehabilitation when relearning certain movement patterns, it is a common practice to focus internally, e.g., on a certain muscle. However, recent scientific evidence suggests an external focus of attention as a solution that maximizes performance when compared to an internal focus of attention. An external focus promotes a greater number of motor solutions, which seems to derive from an "optimal" amount of variability inherent in the motor system. However, the effect of focus of attention on the variability of force/ torque has not been tested experimentally until now. Therefore, the present study investigated the effect of the type of attentional focus (external vs. internal) on the regulation of torque variability and its underlying neurophysiological mechanisms. Fourteen participants performed a submaximal isometric knee extension task, from which measures of torque variability (sample entropy - temporal structure; and coefficient of variation - magnitude of variability) were extracted. Additionally, electromyographic activity of the knee extensor (vastus medialis, vastus lateralis and rectus femoris) and knee flexor (semitendinosus and biceps femoris) muscles was quantified. Furthermore, the co-contraction index between the extensor-flexor pairs was calculated. In the same assessment the participants performed a maximal isometric knee extension task, where peak torque and rate of torque development were extracted. The maximal tasks were performed three times and the submaximal tasks twice per condition (control, internal, external). A one-way repeated measures ANOVA with Tukey's multiple comparisons test, or a Friedman's ANOVA, were used to test the effect of condition. In the submaximal tasks, an internal focus (vs. an external focus) caused a decrease in sample entropy (i.e., increased regularity), whereas for the coefficient of variation a trend in the opposite direction was found. Additionally, an internal focus (vs. an external focus) caused an increase in muscular activity of vastus medialis and semitendinosus. The co-contraction indices involving semitendinosus showed an increase when adopting an internal instead of an external focus. In the maximal tasks, no differences between conditions were found. Taken together, the increase in regularity and in the coefficient of variation are indicators of a reduced motor control caused by an internal focus when compared to an external focus. The fact that an internal focus (vs. an external focus) leads to a general increase in co-contraction and muscular activity, but without affecting maximal force parameters, suggests a lower efficiency of the motor system caused by inter-muscular coordination processes. The present results are of great importance for sport performance as well as in the context of exercise and health, as changes related to instructions and the task goal seem to impact torque regulation and its neurophysiological mechanisms. |
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| Autores principais: | Bauer, Philipp |
| Assunto: | Motor Control Non-linear Dynamics Entropy Torque Complexity Neurophysiology Inter-muscular Coordination Co-contraction Muscular Activity Peak Torque Rate of Torque Development Controlo Motor Dinâmica Não-linear Entropia Complexidade Neurofisiologia Coordenação Intermuscular Co-contração Atividade Muscular Força Máxima Taxa de Produção de Momento de Força |
| Ano: | 2022 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso restrito |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | In strength training, especially in rehabilitation when relearning certain movement patterns, it is a common practice to focus internally, e.g., on a certain muscle. However, recent scientific evidence suggests an external focus of attention as a solution that maximizes performance when compared to an internal focus of attention. An external focus promotes a greater number of motor solutions, which seems to derive from an "optimal" amount of variability inherent in the motor system. However, the effect of focus of attention on the variability of force/ torque has not been tested experimentally until now. Therefore, the present study investigated the effect of the type of attentional focus (external vs. internal) on the regulation of torque variability and its underlying neurophysiological mechanisms. Fourteen participants performed a submaximal isometric knee extension task, from which measures of torque variability (sample entropy - temporal structure; and coefficient of variation - magnitude of variability) were extracted. Additionally, electromyographic activity of the knee extensor (vastus medialis, vastus lateralis and rectus femoris) and knee flexor (semitendinosus and biceps femoris) muscles was quantified. Furthermore, the co-contraction index between the extensor-flexor pairs was calculated. In the same assessment the participants performed a maximal isometric knee extension task, where peak torque and rate of torque development were extracted. The maximal tasks were performed three times and the submaximal tasks twice per condition (control, internal, external). A one-way repeated measures ANOVA with Tukey's multiple comparisons test, or a Friedman's ANOVA, were used to test the effect of condition. In the submaximal tasks, an internal focus (vs. an external focus) caused a decrease in sample entropy (i.e., increased regularity), whereas for the coefficient of variation a trend in the opposite direction was found. Additionally, an internal focus (vs. an external focus) caused an increase in muscular activity of vastus medialis and semitendinosus. The co-contraction indices involving semitendinosus showed an increase when adopting an internal instead of an external focus. In the maximal tasks, no differences between conditions were found. Taken together, the increase in regularity and in the coefficient of variation are indicators of a reduced motor control caused by an internal focus when compared to an external focus. The fact that an internal focus (vs. an external focus) leads to a general increase in co-contraction and muscular activity, but without affecting maximal force parameters, suggests a lower efficiency of the motor system caused by inter-muscular coordination processes. The present results are of great importance for sport performance as well as in the context of exercise and health, as changes related to instructions and the task goal seem to impact torque regulation and its neurophysiological mechanisms. |
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