LINEARITY AND RELIABILITY OF THE IEMG V TORQUE RELATIONSHIP FOR THE FOREARM FLEXORS AND LEG EXTENSORS

The purpose of this investigation was to examine the linearity and reliability of the surface integrated electromyogram (IEMG) v isometric torque relationship for the leg extensors and forearm flexors. Nine men and four women (mean age +/- SD = 22 +/- 2 yr) volunteered for this investigation. Isometric testing was conducted on a Cybex II isokinetic dynamometer with the lever arm at 0.785 rad (45-degrees) below the horizontal plane for the leg extensors and in the vertical plane for the forearm flexors. Bipolar surface electrodes were used to record IEMG values from the vastus lateralis and biceps brachii. To examine test-retest reliability, two test sessions, separated by a minimum of 48 h, were performed. The test-retest linearity of the IEMG v torque relationship ranged from r2 = 0.77 to 0.96 and 0.55 to 0.94 for the forearm flexors and r2 = 0.81 to 0.98 and 0.83 to 0.98 for the leg extensors. The slope values were not significantly different (P > 0.05) between sessions and were correlated (intraclass correlation coefficients) at R = 0.86 (standard error of estimate (SEE) = 5.77 muV . Nm-1, 31% of the mean) and R = 0.97 (SEE = 0.27 muV . Nm-1, 12% of the mean) for the forearm flexors and leg extensors, respectively. The test-retest maximal torque values were 57.73 +/- 22.57 Nm and 58.14 +/- 22.81 Nm (R = 0.99; SEE = 2.39 Nm) for the forearm flexors and 187.79 +/- 55.98 Nm and 195.42 +/- 56.27 Nm (R = 0.96; SEE = 22.62 Nm) for the leg extensors (nonsignificant differences; P > 0.05). Similarly, the test-retest maximal IEMG values were highly correlated (R = 0.95 for forearm flexors and leg extensors) and not significantly different (P > 0.05). The results indicated that the IEMG v torque relationship for the leg extensors exhibited better linearity and reliability than the forearm flexors. For both muscle groups, however, the maximal IEMG and torque values were highly reliable.