Quantifying synergist activation patterns during maximal plantarflexion using an orthogonal expansion approach

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This study sought to determine how well a pattern-recognition approach based on orthogonal-expansion theory can quantify patterns of activation amplitudes that have been recorded by electromyography (EMG) from synergist muscles during isokinetic plantarflexion. Raw surface EMG data were recorded from six muscle sites – four over the agonist Triceps Surae (Lateral and Medial Gastrocnemius, a lateral and a medial site over the Soleus) and two over the antagonist Tibialis Anterior (upper and lower sites) muscles – in ten healthy subjects as they performed three maximal plantarflexor efforts against an isokinetic dynamometer at each of three angular-velocity settings (90 trials). After the root-mean-square amplitude had been calculated for each EMG recording and had been normalized to the amplitude measured during a maximal voluntary isometric contraction, the mean normalized amplitudes were calculated for each muscle site, for the 90 trials. The differences among the muscles and the variability in the normalized amplitudes indicated that the sample mean did not characterize the patterns of relative activation amplitudes among the six muscle sites for all subjects, trials and conditions. An eigenvector decomposition of the normalized data yielded a set of vectors that represents the principal patterns of the activation amplitudes. The principal pattern reflected by eigenvector 1 was 0.57, 0.49, 0.47, 0.45, 0.12 and 0.06 corresponding to the Lateral and Medial Gastrocnemius, the lateral and medial Soleus sites, and the upper and lower sites on the Tibialis Anterior, respectively. The percent trace for eigenvector 1 was 94%; however, two or three eigenvectors were needed to characterize the patterns for some trials. Since 99% of the variance was accounted for by three eigenvectors, the approach was effective in reducing the data while maintaining the salient features in the synergistic patterns of activation amplitudes during isokinetic plantarflexion. PsycINFO classification: 2330; 2530