Vibromyographic quantification of voluntary isometric contractile force in the brachioradialis.

This study investigated the ability of vibromyography (VMG) to accurately represent voluntary forearm muscle contractile force during attempted-isometric contraction of the brachioradialis. VMG signals were collected from the brachioradialis of healthy adult men (mean age, 26.6+/-9.8 years, N=24) during attempted-isometric contraction over a force range of 4.45 N to maximum sustained load. The VMG signals were decomposed using wavelet packet analysis techniques, and the corresponding wavelet packets were utilized in a multiple regression model for parameter reduction and identification of signal components which best correlated to muscle force. It was observed that just two wavelet components were sufficient to accurately predict muscle force (R2=0.984, P<0.0001). The signal force relationship observed is monotonic, though quadratic in form. More importantly, the wavelet data was able to predict absolute force output of the brachioradialis without normalization or prior knowledge of a subject's maximum voluntary force. These data show that VMG recordings are capable of providing a monotonic relationship between VMG signal and muscle force. Moreover, in contrast to EMG technology which can only provide relative force levels, VMG appears to be capable of reporting absolute force levels, an observation which is expected to lead to numerous applications in medicine and rehabilitation.

Reversal of lower limb venous and lymphatic pooling by passive non-invasive calf muscle pump stimulation.

Our preliminary data indicate that exogenous plantar micromechanical stimulation at 45 Hz applied at the plantar surface can prevent tachycardia and blood pressure depression associated with immobility, consistent with improvement in venous and lymphatic fluid return delivered by increased calf muscle activity. In this study, instantaneous beat-to-beat systolic blood pressure of thirty four healthy adult women participants (n=34; age range: 35-78 years) were assessed non-invasively using servo-controlled infra-red finger arterial plethysmography, for 30 minutes in the supine position, followed by 30 minutes in the seated position without plantar stimulation, and lastly for 30 minutes in the seated position with the application of a 45 Hz plantar stimulus (50 microm, p-p). Thirty minutes of supine rest resulted in an average increase of 15 mmHg in systolic pressure. During the 30 minutes of upright sitting regimen, two distinct sub-populations were observed. One group (n=18; "hypotensives") experienced a depression of approximately 15 mmHg in systolic pressure, while the other group (n=16; "normotensives and hypertensives") experienced an elevation in the systolic pressure by approximately 8 mmHg. The subsequent 30 minute application of plantar stimulus reversed the pressure drop in hypotensives and elevated the systolic pressure by approximately 20 mmHg in all the subjects. Plantar-based exogenous micromechanical vibration may be an effective approach for reversal of blood pressure depression associated with the physical stress of immobility over a long term, consistent with enhanced venous and lymphatic fluid return delivered via improved calf muscle contractility.