LOW FREQUENCY PEAK IN ELECTROMYOGRAPHY

Abstract

Purpose: Low frequency peaks (LFP) commonly observed in EMG spectra of paraspinal muscles. These peaks have frequency of 11–15Hz (Median=13, SD=4) and commonly observed in 40% of EMG recordings. We examined the correlation of these peaks with variation in within individuals change in load, between individuals load, gender, age, history of back pain and HW.

Methods and results: Nineteen healthy volunteers were recruited for study of within subject variation in load and data from 106 subjects was examined for the remaining analysis reported here. EMG acquisition was performed using the method described by Oliver et al (Oliver et al., 1996) at a range of load varying from a kilogram to 100% MVC in increments of 10% MVC. The tests were performed in a random order. This method was used for acquisition of data from the second group (n=106) with an exception that only one load fixed at 2/3MVC was used. All parameters including Low frequency peaks and Half Width (HW) was calculated by an automated software developed for this purpose

No correlation between within individual change in load and presence or absence of LFP was found. Only one subject showed a significant correlation between individual change in load with the magnitude of LFPs (r=−0.75, p=0.012). However, when the cumulative data from all 19 subjects was analysed, small correlation between the change in load and magnitude of LFPs (r=−0.17, n=187, p=0.022) was observed, with greater load associated with smaller LFP. No other correlation between gender, individuals load, age and fitness was found.

Conclusion: The appearance of the LFP has been previously described. As yet the underlying cause is not understood, but may be related to a load/feedback loop. The results of this study suggest that load is a factor that may affect LFP and this should be taken into consideration when methods such as HW are used.