Abstract
Study aim: To compare the electromyographic activity during maximal isometric contraction alone or combined with local sinusoidal vibration.
Material and methods: A group of 6 men aged 23 - 29 years performed 3 maximal voluntary contractions of the dominant elbow flexors lasting 10 s each and separated by 5-min intermissions. One repetition was without vibration, one was associated with 15-Hz and the other one with 20-Hz vibrations of 5-mm amplitude, the sequence of repetitions being random. A new system to generate local vibration was applied, the parameters of the vibratory stimulus being measured using an accelerometer. Force and EMG activity were also measured. The subjects performed the task in sitting position in a Scott Bench-type device.
Results: Mean acceleration RMS significantly (p<0.01) differed between vibration frequencies for the X, Y, Z-axes. No significant differences were found, however, for EMG RMS. Vibration frequencies coincided with the machine-predicted ones; acceleration frequencies around 5 Hz were present in all situations, even without vibration, most likely brought about by tremor.
Conclusion: The local vibration applied was not enough to generate different responses in EMG activity. The features of vibratory stimulus confirmed the expected frequency range and revealed frequencies around 5 Hz, that could be attributed to muscle tremor.