Spectrum Analysis of Wireless Electromyography in Water and on Dry Land: A Single Case Example

Recent developments in wireless capture of muscle activity signals have improved the freedom of motion and the ease of use. Nevertheless, no study has examined the quality of wireless electromyographic technology during water activities. In this study the performance of a surface electromyography (SEMG) wireless system on dry land and in water was compared. Tibialis anterior muscle activity of 1 subject while contracting against a resistance of 84 Newton (N) was measured in 2 conditions: using a wireless (KINE) system with waterproof taping on the pool deck and submerged. Analysis of the raw signal showed acceptable ratios of 37 to 44 decibel (dB) between rest activity and the force activity at 84 N in both conditions. The total spectrum analysis and short term frequency analysis showed that no filtering occurred in either of the two conditions as frequencies were picked up in the entire spectrum. Spectrum analysis of rest activity or of the force buildup showed no spikes indicating any pickup of noise. The wireless system produced clean results and submersion and as a consequence recollection from the memory of the unit did not cause additional noise. Furthermore, the wireless system provided a satisfactory signal-to-rest activity ratio of approximately 40 dB and a range of 4 millivolts (mV). The KINE EMG units provided a valid means to analyze muscle activity during swimming while permitting unrestricted movement and ease of use.