VIBROMYOGRAPHY AS A QUANTITATIVE MEASURE OF MUSCLE FORCE PRODUCTION

This study was undertaken to investigate the use of vibromyography (VM G) as a tool for quantifying skeletal muscle force production. Fourtee n healthy volunteers were pretested using a Cybex isokinetic dynamomet er to determine their isometric quadricep maximum voluntary contractio n (MVC) values. On the basis of these results, the subjects were separ ated into two groups: high-forte (''HF'' MVC x = 289 ft.lb., range 254 -330) and low-force (''LF'' MVC x = 154 ft.lb., range 101-198). A vibr omyographic piezoelectric accelerometer (Dytran 3115A) and electromyog raphic (EMG) surface electrodes were affixed to the rectus femoris mus cle and recordings were obtained at 20, 40, 60, 80, and 100% MVC. Root mean squares, median and mean values, were computed from digitized da ta in the time domain while peak values were calculated from a fast Fo urier transform for both the VMG and EMG data. A two-way repeated meas ures MANOVA using relative values and a linear regression model using absolute values were studied using BMDP and MiniTab software. Linear c orrelations mere found between quadricept force and all EMG variables (R(2) range 0.71-0.90) except peak (R(2) = 0.39). The relationship bet ween VMG and force was less linear (R(2) range 0.19-0.69) because VMG values reach a plateau or even drop at 80% and 100% MVC. The HF-LP gro up differences mere significant (p < 0.05), for all VMG values with th e exception of root mean squares, but were not significant (p > 0.05) for all four EMG values. This study shows that, while EMG can discrimi nate force production within a given subject, VMG is a better discrimi nator of absolute muscle force values between subjects, particularly u p to 60% MVC.