Comparison Of Integrated Electromyography During Isometric And Isokinetic Contractions In Normal Subjects

Abstract

Strength is commonly utilized to evaluate recovery from injury using both isometric and isokinetic contractions on dynamometers. Although the torque is traditionally >utilized as the traditional measurement to evaluate strength, little is known about the Integrated Electromyographic (IEMG) activity of the quadriceps and hamstring muscles during rehabilitation exercises. Isometric contractions are associated with higher levels of torque than isokinetic contractions, but may not be associated with higher levels of IEMG. Purpose To determine the dynamometer exercise with the highest level of IEMG activity. Methods Twelve normal subjects performed a 15 minute warm-up on a cycle ergometer, followed by 5 dynamometer exercises: isometric contractions at 30, 60, and 90 degrees of knee extension and isokinetic exercises at 60 degrees/sec and 180 degrees/sec. Both the right and left legs were tested. The order of the exercises and order of left/right leg testing was randomly assigned. IEMG data were collected from the quadriceps muscles (rectus femoris, vastus medialis, and vastus lateralis) and were summed and averaged to obtain the quadriceps IEMG activity. Medial and lateral hamstrings IEMG data were also collected and averaged for the hamstring IEMG activity. Results The normal subjects' hamstring IEMG demonstrated no significant differences between the 5 dynamometer tests (p<0.05). The range of the IEMG was from 342.5 to 385.8. However, the hamstrings IEMG of the right leg was greater (394) than the left leg (335) for the average of the exercises (p<0.5). The quadriceps IEMG showed significant differences with specific exercises (p<0.05). The highest IEMG activities were associated with isometric contraction at 90 degrees (384) and isokinetic contraction at 180 degrees/sec (379) (p<0.05). The isometric tests at 30 degrees (295) and 60 degrees (324) produced significantly less IEMG activity than the other tests (p<0.05). There was no difference between the right (367) and left leg (323) for the quadriceps IEMG for the average of the exercises (p<0.05). Conclusion Normal subjects demonstrated significant differences in the quadriceps IEMG for the different exercises with isokinetic contraction at 180 degrees/sec and isometric contraction at 90 degrees producing the highest levels of quadriceps IEMG. Many exercises will result in maximal hamstring activation; however, isokinetic exercise at 180 degrees/sec or isometric contraction at 90 degrees of knee flexion has been shown to produce maximal quadriceps activation in normal subjects. Further study of these exercises is warranted to verify similar characteristics in rehabilitation patients.