[An electromyographic study of quadriceps muscle force using turns and amplitude analysis]

The relationships between the quadriceps muscle force and electromyographic parameters during isometric and isokinetic knee extension were studied using "turns and amplitude analysis". Two groups of subjects were studied. One group was 40 healthy volunteers whose ages ranged from 16 to 58 years, with a mean of 30.6 years. The other group was 14 patients with unilateral muscle atrophy whose ages ranged from 16 to 53 years, with a mean of 34.2 years. The muscle force was measured using a Cybex II dynamometer, and electromyograms were recorded using a concentric needle electrode, for both groups. In the healthy group, an electromyogram was recorded in the vastus lateralis and vastus medialis, while in the patient group the electromyogram in the vastus lateralis was compared between the atrophied side and the normal side. During isometric knee extension, the muscle showed a significant correlation with amp/turn and turns/sec and the regression curve was expressed as a cubic function. The isokinetic knee extension showed a significant correlation between the muscle force and the amp/turn. In the atrophic muscle, the relationship between the electromyographic parameters and the muscle force was similar to that observed in the normal muscle. The average relative error between the actual muscle power and the calculated muscle power was less for amp/turn than for turns/sec. These results suggest that amp/turn can be used as an electromyographic indicator of quadriceps muscle force.