A Spectral Analysis of Rotator Cuff Musculature Electromyographic Activity: Surface and Indwelling

Sherry I. Backus, PT, DPT, MA
Department of Rehabilitation, Leon Root MD, Motion Analysis Laboratory, Hospital for Special Surgery


Daniel P. Tomlinson, MD
Department of Orthopaedic Surgery, Crystal Run Healthcare


Bavornrat Vanadurongwan, MD
Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University


Mark W. Lenhoff, BS
Department of Rehabilitation, Leon Root MD, Motion Analysis Laboratory, Hospital for Special Surgery


Frank A. Cordasco, MD, MS

Associate Attending Orthopaedic Surgeon, Hospital for Special Surgery
Associate Professor of Orthopaedic Surgery, Weill Cornell Medical College
Surgical Director, Ambulatory Surgery Center, Hospital for Special Surgery
Co-Medical Director, Leon Root Motion Analysis Laboratory, Hospital for Special Surgery

Eric L. Chehab, MD
Department of Orthopaedic Surgery, Illinois Bone and Joint Institute


Ronald S. Adler, PhD, MD
Chief, Division of Ultrasound and Body CT, Radiology and Imaging, Hospital for Special Surgery
Attending Radiologist, Hospital for Special Surgery
Attending Radiologist, New York Presbyterian Hospital
Professor of Radiology, Weill Cornell Medical College
Research Scientist, Hospital for Special Surgery


R. Frank Henn III, MD
Hospital for Special Surgery


Howard J. Hillstrom, PhD
Department of Rehabilitation, Leon Root MD, Motion Analysis Laboratory, Hospital for Special Surgery


Abstract

Electromyography (EMG) of the shoulder girdle is commonly performed; however, EMG spectral properties of shoulder muscles have not been clearly defined. The purpose of this study was to determine the maximum power frequency, Nyquist rate, and minimum sampling rate for indwelling and surface EMG of the normal shoulder girdle musculature. EMG signals were recorded using indwelling electrodes for the rotator cuff muscles and surface electrodes for ten additional shoulder muscles in ten healthy volunteers. A fast Fourier transform was performed on the raw EMG signal collected during maximal isometric contractions to derive the power spectral density. The 95% power frequency was calculated during the ramp and plateau subphase of each contraction. Data were analyzed with analysis of variance (ANOVA) and paired t tests. Indwelling EMG signals had more than twice the frequency content of surface EMG signals (p#<#.001). Mean 95% power frequencies ranged from 495 to 560 Hz for indwelling electrodes and from 152 to 260 Hz for surface electrodes. Significant differences in the mean 95% power frequencies existed among muscles monitored with surface electrodes (p#=#.002), but not among muscles monitored with indwelling electrodes (p#=#.961). No significant differences in the 95% power frequencies existed among contraction subphases for any of the muscle–electrode combinations. Maximum Nyquist rate was 893 Hz for surface electrodes and 1,764 Hz for indwelling electrodes. Our results suggest that when recording EMG of shoulder muscles, the minimum sampling frequency is 1,340 Hz for surface electrodes and 2,650 Hz for indwelling electrodes. The minimum sampling recommendations are higher than the 1,000 Hz reported in many studies involving EMG of the shoulder.

This article appears in HSS Journal: Volume 7, Number 1.
View the full article at springerlink.com.

About the HSS Journal
HSS Journal, an academic peer-reviewed journal, is published twice a year, February and September, and features articles by internal faculty and HSS alumni that present current research and clinical work in the field of musculoskeletal medicine performed at HSS, including research articles, surgical procedures, and case reports.


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