Surface EMG alterations induced by under water recording. A case study

Rainoldi, Alberto and Cescon, Corrado and Bottin, Andrea and Merletti, Roberto (2002) Surface EMG alterations induced by under water recording. A case study. In: Proc. of the XIV Congress of the International Society of Electrophysiology and Kinesiology, 22-25 June 2002, Vienna, Austria.

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Rehabilitation treatments in exercise pools are often prescribed during the initial phase of rehabilitation programs. They are often associated to surface EMG recordings to check proper muscular activation during movements or to monitor the effects of treatments. Although EMG recordings in water are widely used, there are no reports in literature validating or standardizing the methodological aspects of the technique. This study aims to verify if amplitude and spectral characteristics of surface EMG signal are modified due to recording in a wet environment. Isometric contractions of the abductor digiti minimi muscle were performed in several different set-up combinations, both in dry (D) and wet environment, both with distilled water (DW) and with water from hydrotherapy pools (PW), both with adhesive (AE) and clip electrodes (CE), with (T) and without water-resistant adhesive taping. In all the conditions, except T, the amplitude of the recorded signal is reduced to 5-10% of the corresponding signal recorded in D. The power spectrum is drastically reduced and altered by the water movement that causes a power increase in the range 0-25 Hz. The use of T modality allows to record signals with both amplitude and spectral variables comparable with those obtained in the D conditions. This work demonstrates the need to prevent any contact between water and non insulated electrodes, connectors and cables. Signals recorded without such precautions are strongly affected in their amplitude and frequency characteristics, their information content is deeply modified and becomes useless for clinical purposes.

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