Muscle Strength as a Predictor of the Magnitude of Multidirectional Force Fluctuations during Steady Contractions

摘要

It has been shown that, during static contrac tions, the standard deviation of force increases linearly as the target force increases due to the orderly recruitment of motor units. In addition, previous studies suggested that larger mus cle groups present lower normalized force fluctuations. The aim of the present study was to test the generalization of these two principles by the assessment of three-dimensional force fluctuations of different muscle groups during steady contrac tions of dorsiflexors, elbow flexors, trunk extensors, knee ex tensors, and plantarflexors. According to the results, although significant linear correlations exist between MVC forces and the different parameters of variability assessed, no clear rela tionship was found when the mean values were compared across muscle groups. Moreover, the present data demonstrate that high fluctuations of the task-related force component do not necessarily imply in high fluctuations of tangential compo nents. Hence, factors such as co-contraction and the number of degrees of freedom in the joints might also account for the variability of multidirectional forces.