Effect of feedback type and training on voluntary control of single motor units

McNaught, Andrew and Cescon, Corrado and Vieira, Taian M. M. and Lester, John and Merletti, Roberto (2010) Effect of feedback type and training on voluntary control of single motor units. In: Proceedings of the VII Motor Control Conference - MCC, 24-27 Sept 2010, Varna, Bulgaria.

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AIMS. To investigate the capability of humans to control activation and firing rate of single motor units (MUs) through visual and audio feedback of the surface electromyographic (sEMG) signal. As humans are naturally able to control muscle force and are unaware of muscle activity on the single MU level, such control would have to be learned through training with feedback. Combinations of visual and audio feedback were investigated with the goal of determining the best feedback to use for such training. METHODS. Sixteen healthy volunteers, male and female, with little or no experience with EMG, participated in the study. Single Differential sEMG signals were acquired from the abductor pollicis brevis (APB) muscle of the right hand during isometric contractions with a 15-channel dry electrode grid (Figure 1d) and multichannel EMG amplifier (EMG-USB, OT Bioelettronica). Real-time MU detection was achieved through window comparator peak detection of a filtered feedback EMG signal. The MU firing rate was calculated from the number of detected peaks in a moving window of 1s. Visual feedback consisted of: five channels of raw EMG (Figure 1a), one channel of feedback EMG (Figure1 b), firing rate speedometer (Figure 1c). Audio feedback: low tone beep when a MU peak was detected within the desired window comparator, high tone beep when a MU peak was above the window comparator. Testing was conducted in three sessions: before, after 15 minutes and after 30 minutes of training. The tests evaluated control of MU activation and firing rate, requiring subjects to isolate a single observable MU, maintain it’s firing rate and modulate the firing rate between low and high firing levels. Further tests were conducted to assess the types of feedback provided. RESULTS. Before training, subjects found it difficult to isolate a single MU peak within the specified window comparator (Figure 1e). After 15 minutes of training an improvement was observed, and after 30 minutes of training many subjects were performing the tests well, as can be seen in Figure 1f. Subjects found the raw EMG visual feedback to be confusing and all indicated that the MU firing rate speedometer and MU peak audio feedback were preferable and crucial in the training process. CONCLUSIONS. Individuals without any prior experience or knowledge of electromyography or motor unit physiology show the ability to learn control of a single MU through feedback of MU features (activation and firing rate) from surface EMG. The simplest forms of feedback (direct visual and audio indication of MU features) seem to be the most useful for individuals inexperienced in EMG techniques.

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