Voluntary activation in the triceps brachii at short and long muscle lengths

The aim was of this study was to determine whether voluntary activation calculated using the interpolated twitch technique (ITT) would be underestimated by muscle length-induced changes in the twitch amplitude evoked at rest after maximum voluntary contraction (MVC) in the elbow extensors. In 12 healthy men, calculated voluntary activations were compared at short (20 degrees of elbow flexion) and long muscle lengths (120 degrees ) using the actual post-MVC doublet, and the predicted post-MVC doublet estimated from linear or nonlinear extrapolations. Actual post-MVC doublet amplitudes were smaller at 20 degrees versus 120 degrees . At 20 degrees , the predicted post-MVC doublet obtained from nonlinear extrapolation was larger, and voluntary activation values improved by 5-33% at the submaximal voluntary contraction intensities (< or =80% of MVC). When voluntary drive is compromised, this method of extrapolation is useful to account for mechanical limitations that blunt the actual post-MVC doublet, which otherwise leads to underestimation of voluntary activation.