The motor unit action potentials(MUAP) of the needle EMG are analyzed morphologically in time domain generally. The limitations of the morphological analysis of the MUAP make the electromyographer to hesitate making the diagnosis in clinic, because of its complexity. We introduced the power spectrum to the analysis of the MUAP in this study, and its clinical values were evaluated.

42 Sprang-Dawley rats were grouped according to the duration of the nerve injury(normal, n=10; post-operative 3rd week, n=10; post-operative 4th week, n=11; post-operative 8th week, n=11). Crushing nerve injury was applied to the left sciatic nerve between the sciatic notch and the knee. Sciatic motor nerve conduction study, turn/amplitude analysis, and power spectral analysis of the MUAP in the M. Tibialis anterior were evaluated on both sides in all groups.

Results
were as followings.

1) The amplitudes of the sciatic motor nerve conduction got to the normal range at 8th week after the nerve injury.

2) The turn/amplitude analysis had no statistical significance to differentiate the MUAP of the unaffected from the affected muscles at the 8th week after the nerve injury in this study(P>0.1).

3) The power spectral analysis had no ability to discriminate the MUAP among the affected and the unaffected muscles at the 8th week after the nerve injury in terms of the total power and the frequency range(P>0.1). But the changes in the ratio of the power in each range (high to total, middle to total, low to total) were significant to differentiate the nerve-injured from the control rat. Increment of the ratio of the middle(151~300Hz) and low(51~300) frequency power was noticed in both of the affected and unaffected muscles in the nerve-injured rats(P<0.05).

4) In terms of the MUAP according to the interference and amplitudes, the proportional ratios of the power spectrum were different between the affected and the unaffected muscles of the nerve-injured rat at 8th week after the crushing.

In conclusion, the power spectral analysis of the MUAP could contribute to improve the range of diagnosis of the MUAP abnormality.