Vibromyographic Research Articles

Changes in postural muscle dynamics as a function of age.

Histologic studies have demonstrated both a decrease in size and loss in number of type II muscle fibers with increasing age. Although these age-related histologic changes are believed to result in decreased strength and functional capacity, age-related changes in muscle force dynamics have not been clearly elucidated. Using vibromyographic (VMG) techniques, we recorded muscle activity of the soleus in 40 healthy adult volunteers spanning the age range of 20-82 years to test whether changes in postural muscle dynamics, in the frequency range of 0.1-50 Hz, were also associated with age. Although muscle dynamics below 15 Hz do not change with aging, the 30-50 Hz frequency components of the VMG were found to change significantly with advancing age (r = -.619, p = .0001). This was observed in both sexes independently. The observed age-related changes in muscle force dynamics demonstrate distinct physiologic alterations in muscle fiber activity. Further research will be required to fully elucidate the relationship between age-related changes in muscle fiber activity and other age-related conditions such as postural instability and osteoporosis.

Relationships of Vibromyographic and Electromyographic Signals During Isometric Voluntary Contraction

Summary The relationships of the vibromyographic (VMG) and the electromyographic (EMG) signals during different levels of isometric voluntary contraction were investigated in an experiment on the rectus femoris muscle of five young men. Each subject performed five different levels of contraction (20, 40, 60, 80 and 100% isometric maximal voluntary contraction — IMVC) in random order. Simultaneous recording of the VMG and EMG signals was obtained from the rectus femoris muscle. Regression analysis was used to examine the relationship between the root mean square (rms-VMG, rms-EMG, median frequency (MF) of VMG and MF-EMG with different levels of contraction. Results show that the rms-VMG and rms-EMG increase in a similar fashion with increase in percentage of IMVC. Regression analysis shows a strong positive linear relationship of the VMG and EMG with the level of contraction (r 2 = 0.66, p 2 = 0.87, p 2 = 0.58, p 2 = 0.31, P The result of the present study shows a linear relationship between the VMG and the EMG signals, in both the time domain (rms) and the frequency domain (MF), with the level of voluntary isometric contraction. A recording and analysis of the EMG and VMG signals may provide a reliable indicator to investigate simultaneously the electrophysiological and mechanical properties of the muscle at different levels of contraction.

The effect of muscle length on electrically elicited muscle vibrations in the in-situ cat soleus muscle

The effects of length changes in the in-situ cat soleus muscle on vibromyographic (VMG) signals were assessed using electrical stimulation of the soleus nerve in three adult male cats. Force and VMG signals were measured using an E-shaped force transducer and a miniature, unidirectional accelerometer, respectively. In each test, the soleus nerve was stimulated for 6 s at rates ranging from 4 to 35 Hz, and at two to four ankle angles (80–140 °). The force of the soleus muscle increased with increasing muscle length and stimulation rates. For a given sub-tetanic frequency of stimulation, the root mean square (RMS) values of the VMG signal were larger at intermediate muscle lengths than at both the longest and the shortest muscle lengths. There was a continuous increase in the RMS of the VMG signal with decreasing muscle length when the contraction was tetanic. There was a trend towards an increase in the median frequency (MDF) of the VMG signal with increasing muscle length. The results of this study support the idea that the amplitude and frequency content of the VMG signal during electrically elicited muscle contractions are directly affected by changes in the mechanical properties (i.e. the stiffness and the active and passive tension) of muscle caused by length changes.