Effective muscle synergies extraction pipeline to characterise the Box and Block Test movement

The Box and Block test (BBT) is a clinical test for the evaluation of the unilateral manual dexterity. To the best of our knowledge, no study has yet explored it through the muscle synergy approach. Since each analysis step impacts on the muscle synergies influencing the results interpretation, this study aims at i) optimising the procedure of muscular synergies extraction in BBT and ii) applying it to characterise BBT in healthy individuals. Electromyographic (EMG) data (8 muscles per arm) were recorded from 16 participants during the BBT performed with each upper limb, separately. Muscle synergies were extracted by means of the Non-Negative Matrix Factorization method and the impact of following two parameters was estimated: (i) cut-off frequency of lowpass filter designed to compute the envelope of the EMG signals (ii) type of normalisation to be applied to the EMG envelopes. Results show that the procedure of muscular synergies extraction requires to be optimised with particular attention to the cut-off frequency of low-pass filter designed to compute the envelope of the EMG signals and the type of normalisation to be applied to the EMG envelopes. From the physiological perspective, three synergies seem to be enough to capture main BBT movement mechanisms. The evaluation of the impact of processing steps on the muscle synergies and the characterization of the BBT will pave the way for the definition of a standard procedure to be applied also in a pathological context.